Skip to content
Snippets Groups Projects
Select Git revision
  • benchmark-tools
  • postgres-lambda
  • master default
  • REL9_4_25
  • REL9_5_20
  • REL9_6_16
  • REL_10_11
  • REL_11_6
  • REL_12_1
  • REL_12_0
  • REL_12_RC1
  • REL_12_BETA4
  • REL9_4_24
  • REL9_5_19
  • REL9_6_15
  • REL_10_10
  • REL_11_5
  • REL_12_BETA3
  • REL9_4_23
  • REL9_5_18
  • REL9_6_14
  • REL_10_9
  • REL_11_4
23 results

xlog.c

Blame
  • xlog.c 265.86 KiB
    /*-------------------------------------------------------------------------
     *
     * xlog.c
     *		PostgreSQL transaction log manager
     *
     *
     * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group
     * Portions Copyright (c) 1994, Regents of the University of California
     *
     * $PostgreSQL: pgsql/src/backend/access/transam/xlog.c,v 1.382 2010/03/18 09:17:18 heikki Exp $
     *
     *-------------------------------------------------------------------------
     */
    
    #include "postgres.h"
    
    #include <ctype.h>
    #include <signal.h>
    #include <time.h>
    #include <fcntl.h>
    #include <sys/stat.h>
    #include <sys/time.h>
    #include <sys/wait.h>
    #include <unistd.h>
    
    #include "access/clog.h"
    #include "access/multixact.h"
    #include "access/subtrans.h"
    #include "access/transam.h"
    #include "access/tuptoaster.h"
    #include "access/twophase.h"
    #include "access/xact.h"
    #include "access/xlog_internal.h"
    #include "access/xlogutils.h"
    #include "catalog/catversion.h"
    #include "catalog/pg_control.h"
    #include "catalog/pg_database.h"
    #include "catalog/pg_type.h"
    #include "funcapi.h"
    #include "libpq/pqsignal.h"
    #include "miscadmin.h"
    #include "pgstat.h"
    #include "postmaster/bgwriter.h"
    #include "replication/walreceiver.h"
    #include "replication/walsender.h"
    #include "storage/bufmgr.h"
    #include "storage/fd.h"
    #include "storage/ipc.h"
    #include "storage/pmsignal.h"
    #include "storage/procarray.h"
    #include "storage/smgr.h"
    #include "storage/spin.h"
    #include "utils/builtins.h"
    #include "utils/guc.h"
    #include "utils/ps_status.h"
    #include "utils/relmapper.h"
    #include "pg_trace.h"
    
    
    /* File path names (all relative to $PGDATA) */
    #define BACKUP_LABEL_FILE		"backup_label"
    #define BACKUP_LABEL_OLD		"backup_label.old"
    #define RECOVERY_COMMAND_FILE	"recovery.conf"
    #define RECOVERY_COMMAND_DONE	"recovery.done"
    
    
    /* User-settable parameters */
    int			CheckPointSegments = 3;
    int			XLOGbuffers = 8;
    int			XLogArchiveTimeout = 0;
    bool		XLogArchiveMode = false;
    char	   *XLogArchiveCommand = NULL;
    bool		XLogRequestRecoveryConnections = true;
    int			MaxStandbyDelay = 30;
    bool		fullPageWrites = true;
    bool		log_checkpoints = false;
    int			sync_method = DEFAULT_SYNC_METHOD;
    
    #ifdef WAL_DEBUG
    bool		XLOG_DEBUG = false;
    #endif
    
    /*
     * XLOGfileslop is the maximum number of preallocated future XLOG segments.
     * When we are done with an old XLOG segment file, we will recycle it as a
     * future XLOG segment as long as there aren't already XLOGfileslop future
     * segments; else we'll delete it.  This could be made a separate GUC
     * variable, but at present I think it's sufficient to hardwire it as
     * 2*CheckPointSegments+1.	Under normal conditions, a checkpoint will free
     * no more than 2*CheckPointSegments log segments, and we want to recycle all
     * of them; the +1 allows boundary cases to happen without wasting a
     * delete/create-segment cycle.
     */
    #define XLOGfileslop	(2*CheckPointSegments + 1)
    
    /*
     * GUC support
     */
    const struct config_enum_entry sync_method_options[] = {
    	{"fsync", SYNC_METHOD_FSYNC, false},
    #ifdef HAVE_FSYNC_WRITETHROUGH
    	{"fsync_writethrough", SYNC_METHOD_FSYNC_WRITETHROUGH, false},
    #endif
    #ifdef HAVE_FDATASYNC
    	{"fdatasync", SYNC_METHOD_FDATASYNC, false},
    #endif
    #ifdef OPEN_SYNC_FLAG
    	{"open_sync", SYNC_METHOD_OPEN, false},
    #endif
    #ifdef OPEN_DATASYNC_FLAG
    	{"open_datasync", SYNC_METHOD_OPEN_DSYNC, false},
    #endif
    	{NULL, 0, false}
    };
    
    /*
     * Statistics for current checkpoint are collected in this global struct.
     * Because only the background writer or a stand-alone backend can perform
     * checkpoints, this will be unused in normal backends.
     */
    CheckpointStatsData CheckpointStats;
    
    /*
     * ThisTimeLineID will be same in all backends --- it identifies current
     * WAL timeline for the database system.
     */
    TimeLineID	ThisTimeLineID = 0;
    
    /*
     * Are we doing recovery from XLOG?
     *
     * This is only ever true in the startup process; it should be read as meaning
     * "this process is replaying WAL records", rather than "the system is in
     * recovery mode".  It should be examined primarily by functions that need
     * to act differently when called from a WAL redo function (e.g., to skip WAL
     * logging).  To check whether the system is in recovery regardless of which
     * process you're running in, use RecoveryInProgress() but only after shared
     * memory startup and lock initialization.
     */
    bool		InRecovery = false;
    
    /* Are we in Hot Standby mode? Only valid in startup process, see xlog.h */
    HotStandbyState standbyState = STANDBY_DISABLED;
    
    static XLogRecPtr LastRec;
    
    /*
     * Local copy of SharedRecoveryInProgress variable. True actually means "not
     * known, need to check the shared state".
     */
    static bool LocalRecoveryInProgress = true;
    
    /*
     * Local state for XLogInsertAllowed():
     *		1: unconditionally allowed to insert XLOG
     *		0: unconditionally not allowed to insert XLOG
     *		-1: must check RecoveryInProgress(); disallow until it is false
     * Most processes start with -1 and transition to 1 after seeing that recovery
     * is not in progress.	But we can also force the value for special cases.
     * The coding in XLogInsertAllowed() depends on the first two of these states
     * being numerically the same as bool true and false.
     */
    static int	LocalXLogInsertAllowed = -1;
    
    /* Are we recovering using offline XLOG archives? */
    static bool InArchiveRecovery = false;
    
    /* Was the last xlog file restored from archive, or local? */
    static bool restoredFromArchive = false;
    
    /* options taken from recovery.conf for archive recovery */
    static char *recoveryRestoreCommand = NULL;
    static char *recoveryEndCommand = NULL;
    static char *restartPointCommand = NULL;
    static bool recoveryTarget = false;
    static bool recoveryTargetExact = false;
    static bool recoveryTargetInclusive = true;
    static TransactionId recoveryTargetXid;
    static TimestampTz recoveryTargetTime;
    static TimestampTz recoveryLastXTime = 0;
    
    /* options taken from recovery.conf for XLOG streaming */
    static bool StandbyMode = false;
    static char *PrimaryConnInfo = NULL;
    char	   *TriggerFile = NULL;
    
    /* if recoveryStopsHere returns true, it saves actual stop xid/time here */
    static TransactionId recoveryStopXid;
    static TimestampTz recoveryStopTime;
    static bool recoveryStopAfter;
    
    /*
     * During normal operation, the only timeline we care about is ThisTimeLineID.
     * During recovery, however, things are more complicated.  To simplify life
     * for rmgr code, we keep ThisTimeLineID set to the "current" timeline as we
     * scan through the WAL history (that is, it is the line that was active when
     * the currently-scanned WAL record was generated).  We also need these
     * timeline values:
     *
     * recoveryTargetTLI: the desired timeline that we want to end in.
     *
     * expectedTLIs: an integer list of recoveryTargetTLI and the TLIs of
     * its known parents, newest first (so recoveryTargetTLI is always the
     * first list member).	Only these TLIs are expected to be seen in the WAL
     * segments we read, and indeed only these TLIs will be considered as
     * candidate WAL files to open at all.
     *
     * curFileTLI: the TLI appearing in the name of the current input WAL file.
     * (This is not necessarily the same as ThisTimeLineID, because we could
     * be scanning data that was copied from an ancestor timeline when the current
     * file was created.)  During a sequential scan we do not allow this value
     * to decrease.
     */
    static TimeLineID recoveryTargetTLI;
    static List *expectedTLIs;
    static TimeLineID curFileTLI;
    
    /*
     * ProcLastRecPtr points to the start of the last XLOG record inserted by the
     * current backend.  It is updated for all inserts.  XactLastRecEnd points to
     * end+1 of the last record, and is reset when we end a top-level transaction,
     * or start a new one; so it can be used to tell if the current transaction has
     * created any XLOG records.
     */
    static XLogRecPtr ProcLastRecPtr = {0, 0};
    
    XLogRecPtr	XactLastRecEnd = {0, 0};
    
    /*
     * RedoRecPtr is this backend's local copy of the REDO record pointer
     * (which is almost but not quite the same as a pointer to the most recent
     * CHECKPOINT record).	We update this from the shared-memory copy,
     * XLogCtl->Insert.RedoRecPtr, whenever we can safely do so (ie, when we
     * hold the Insert lock).  See XLogInsert for details.	We are also allowed
     * to update from XLogCtl->Insert.RedoRecPtr if we hold the info_lck;
     * see GetRedoRecPtr.  A freshly spawned backend obtains the value during
     * InitXLOGAccess.
     */
    static XLogRecPtr RedoRecPtr;
    
    /*
     * RedoStartLSN points to the checkpoint's REDO location which is specified
     * in a backup label file, backup history file or control file. In standby
     * mode, XLOG streaming usually starts from the position where an invalid
     * record was found. But if we fail to read even the initial checkpoint
     * record, we use the REDO location instead of the checkpoint location as
     * the start position of XLOG streaming. Otherwise we would have to jump
     * backwards to the REDO location after reading the checkpoint record,
     * because the REDO record can precede the checkpoint record.
     */
    static XLogRecPtr RedoStartLSN = {0, 0};
    
    /*----------
     * Shared-memory data structures for XLOG control
     *
     * LogwrtRqst indicates a byte position that we need to write and/or fsync
     * the log up to (all records before that point must be written or fsynced).
     * LogwrtResult indicates the byte positions we have already written/fsynced.
     * These structs are identical but are declared separately to indicate their
     * slightly different functions.
     *
     * We do a lot of pushups to minimize the amount of access to lockable
     * shared memory values.  There are actually three shared-memory copies of
     * LogwrtResult, plus one unshared copy in each backend.  Here's how it works:
     *		XLogCtl->LogwrtResult is protected by info_lck
     *		XLogCtl->Write.LogwrtResult is protected by WALWriteLock
     *		XLogCtl->Insert.LogwrtResult is protected by WALInsertLock
     * One must hold the associated lock to read or write any of these, but
     * of course no lock is needed to read/write the unshared LogwrtResult.
     *
     * XLogCtl->LogwrtResult and XLogCtl->Write.LogwrtResult are both "always
     * right", since both are updated by a write or flush operation before
     * it releases WALWriteLock.  The point of keeping XLogCtl->Write.LogwrtResult
     * is that it can be examined/modified by code that already holds WALWriteLock
     * without needing to grab info_lck as well.
     *
     * XLogCtl->Insert.LogwrtResult may lag behind the reality of the other two,
     * but is updated when convenient.	Again, it exists for the convenience of
     * code that is already holding WALInsertLock but not the other locks.
     *
     * The unshared LogwrtResult may lag behind any or all of these, and again
     * is updated when convenient.
     *
     * The request bookkeeping is simpler: there is a shared XLogCtl->LogwrtRqst
     * (protected by info_lck), but we don't need to cache any copies of it.
     *
     * Note that this all works because the request and result positions can only
     * advance forward, never back up, and so we can easily determine which of two
     * values is "more up to date".
     *
     * info_lck is only held long enough to read/update the protected variables,
     * so it's a plain spinlock.  The other locks are held longer (potentially
     * over I/O operations), so we use LWLocks for them.  These locks are:
     *
     * WALInsertLock: must be held to insert a record into the WAL buffers.
     *
     * WALWriteLock: must be held to write WAL buffers to disk (XLogWrite or
     * XLogFlush).
     *
     * ControlFileLock: must be held to read/update control file or create
     * new log file.
     *
     * CheckpointLock: must be held to do a checkpoint or restartpoint (ensures
     * only one checkpointer at a time; currently, with all checkpoints done by
     * the bgwriter, this is just pro forma).
     *
     *----------
     */
    
    typedef struct XLogwrtRqst
    {
    	XLogRecPtr	Write;			/* last byte + 1 to write out */
    	XLogRecPtr	Flush;			/* last byte + 1 to flush */
    } XLogwrtRqst;
    
    typedef struct XLogwrtResult
    {
    	XLogRecPtr	Write;			/* last byte + 1 written out */
    	XLogRecPtr	Flush;			/* last byte + 1 flushed */
    } XLogwrtResult;
    
    /*
     * Shared state data for XLogInsert.
     */
    typedef struct XLogCtlInsert
    {
    	XLogwrtResult LogwrtResult; /* a recent value of LogwrtResult */
    	XLogRecPtr	PrevRecord;		/* start of previously-inserted record */
    	int			curridx;		/* current block index in cache */
    	XLogPageHeader currpage;	/* points to header of block in cache */
    	char	   *currpos;		/* current insertion point in cache */
    	XLogRecPtr	RedoRecPtr;		/* current redo point for insertions */
    	bool		forcePageWrites;	/* forcing full-page writes for PITR? */
    } XLogCtlInsert;
    
    /*
     * Shared state data for XLogWrite/XLogFlush.
     */
    typedef struct XLogCtlWrite
    {
    	XLogwrtResult LogwrtResult; /* current value of LogwrtResult */
    	int			curridx;		/* cache index of next block to write */
    	pg_time_t	lastSegSwitchTime;		/* time of last xlog segment switch */
    } XLogCtlWrite;
    
    /*
     * Total shared-memory state for XLOG.
     */
    typedef struct XLogCtlData
    {
    	/* Protected by WALInsertLock: */
    	XLogCtlInsert Insert;
    
    	/* Protected by info_lck: */
    	XLogwrtRqst LogwrtRqst;
    	XLogwrtResult LogwrtResult;
    	uint32		ckptXidEpoch;	/* nextXID & epoch of latest checkpoint */
    	TransactionId ckptXid;
    	XLogRecPtr	asyncCommitLSN; /* LSN of newest async commit */
    
    	/* Protected by WALWriteLock: */
    	XLogCtlWrite Write;
    
    	/*
    	 * These values do not change after startup, although the pointed-to pages
    	 * and xlblocks values certainly do.  Permission to read/write the pages
    	 * and xlblocks values depends on WALInsertLock and WALWriteLock.
    	 */
    	char	   *pages;			/* buffers for unwritten XLOG pages */
    	XLogRecPtr *xlblocks;		/* 1st byte ptr-s + XLOG_BLCKSZ */
    	int			XLogCacheBlck;	/* highest allocated xlog buffer index */
    	TimeLineID	ThisTimeLineID;
    	TimeLineID	RecoveryTargetTLI;
    	/*
    	 * restartPointCommand is read from recovery.conf but needs to be in
    	 * shared memory so that the bgwriter process can access it.
    	 */
    	char		restartPointCommand[MAXPGPATH];
    
    	/*
    	 * SharedRecoveryInProgress indicates if we're still in crash or archive
    	 * recovery.  Protected by info_lck.
    	 */
    	bool		SharedRecoveryInProgress;
    
    	/*
    	 * During recovery, we keep a copy of the latest checkpoint record here.
    	 * Used by the background writer when it wants to create a restartpoint.
    	 *
    	 * Protected by info_lck.
    	 */
    	XLogRecPtr	lastCheckPointRecPtr;
    	CheckPoint	lastCheckPoint;
    
    	/* end+1 of the last record replayed (or being replayed) */
    	XLogRecPtr	replayEndRecPtr;
    	/* timestamp of last record replayed (or being replayed) */
    	TimestampTz recoveryLastXTime;
    	/* end+1 of the last record replayed */
    	XLogRecPtr	recoveryLastRecPtr;
    
    	slock_t		info_lck;		/* locks shared variables shown above */
    } XLogCtlData;
    
    static XLogCtlData *XLogCtl = NULL;
    
    /*
     * We maintain an image of pg_control in shared memory.
     */
    static ControlFileData *ControlFile = NULL;
    
    /*
     * Macros for managing XLogInsert state.  In most cases, the calling routine
     * has local copies of XLogCtl->Insert and/or XLogCtl->Insert->curridx,
     * so these are passed as parameters instead of being fetched via XLogCtl.
     */
    
    /* Free space remaining in the current xlog page buffer */
    #define INSERT_FREESPACE(Insert)  \
    	(XLOG_BLCKSZ - ((Insert)->currpos - (char *) (Insert)->currpage))
    
    /* Construct XLogRecPtr value for current insertion point */
    #define INSERT_RECPTR(recptr,Insert,curridx)  \
    	( \
    	  (recptr).xlogid = XLogCtl->xlblocks[curridx].xlogid, \
    	  (recptr).xrecoff = \
    		XLogCtl->xlblocks[curridx].xrecoff - INSERT_FREESPACE(Insert) \
    	)
    
    #define PrevBufIdx(idx)		\
    		(((idx) == 0) ? XLogCtl->XLogCacheBlck : ((idx) - 1))
    
    #define NextBufIdx(idx)		\
    		(((idx) == XLogCtl->XLogCacheBlck) ? 0 : ((idx) + 1))
    
    /*
     * Private, possibly out-of-date copy of shared LogwrtResult.
     * See discussion above.
     */
    static XLogwrtResult LogwrtResult = {{0, 0}, {0, 0}};
    
    /*
     * openLogFile is -1 or a kernel FD for an open log file segment.
     * When it's open, openLogOff is the current seek offset in the file.
     * openLogId/openLogSeg identify the segment.  These variables are only
     * used to write the XLOG, and so will normally refer to the active segment.
     */
    static int	openLogFile = -1;
    static uint32 openLogId = 0;
    static uint32 openLogSeg = 0;
    static uint32 openLogOff = 0;
    
    /*
     * These variables are used similarly to the ones above, but for reading
     * the XLOG.  Note, however, that readOff generally represents the offset
     * of the page just read, not the seek position of the FD itself, which
     * will be just past that page. readLen indicates how much of the current
     * page has been read into readBuf.
     */
    static int	readFile = -1;
    static uint32 readId = 0;
    static uint32 readSeg = 0;
    static uint32 readOff = 0;
    static uint32 readLen = 0;
    
    /* Is the currently open segment being streamed from primary? */
    static bool readStreamed = false;
    
    /* Buffer for currently read page (XLOG_BLCKSZ bytes) */
    static char *readBuf = NULL;
    
    /* Buffer for current ReadRecord result (expandable) */
    static char *readRecordBuf = NULL;
    static uint32 readRecordBufSize = 0;
    
    /* State information for XLOG reading */
    static XLogRecPtr ReadRecPtr;	/* start of last record read */
    static XLogRecPtr EndRecPtr;	/* end+1 of last record read */
    static TimeLineID lastPageTLI = 0;
    
    static XLogRecPtr minRecoveryPoint;		/* local copy of
    										 * ControlFile->minRecoveryPoint */
    static bool updateMinRecoveryPoint = true;
    
    static bool InRedo = false;
    
    /*
     * Flags set by interrupt handlers for later service in the redo loop.
     */
    static volatile sig_atomic_t got_SIGHUP = false;
    static volatile sig_atomic_t shutdown_requested = false;
    
    /*
     * Flag set when executing a restore command, to tell SIGTERM signal handler
     * that it's safe to just proc_exit.
     */
    static volatile sig_atomic_t in_restore_command = false;
    
    
    static void XLogArchiveNotify(const char *xlog);
    static void XLogArchiveNotifySeg(uint32 log, uint32 seg);
    static bool XLogArchiveCheckDone(const char *xlog);
    static bool XLogArchiveIsBusy(const char *xlog);
    static void XLogArchiveCleanup(const char *xlog);
    static void readRecoveryCommandFile(void);
    static void exitArchiveRecovery(TimeLineID endTLI,
    					uint32 endLogId, uint32 endLogSeg);
    static bool recoveryStopsHere(XLogRecord *record, bool *includeThis);
    static void CheckRequiredParameterValues(CheckPoint checkPoint);
    static void LocalSetXLogInsertAllowed(void);
    static void CheckPointGuts(XLogRecPtr checkPointRedo, int flags);
    
    static bool XLogCheckBuffer(XLogRecData *rdata, bool doPageWrites,
    				XLogRecPtr *lsn, BkpBlock *bkpb);
    static bool AdvanceXLInsertBuffer(bool new_segment);
    static void XLogWrite(XLogwrtRqst WriteRqst, bool flexible, bool xlog_switch);
    static bool InstallXLogFileSegment(uint32 *log, uint32 *seg, char *tmppath,
    					   bool find_free, int *max_advance,
    					   bool use_lock);
    static int XLogFileRead(uint32 log, uint32 seg, int emode, TimeLineID tli,
    			 bool fromArchive, bool notexistOk);
    static int XLogFileReadAnyTLI(uint32 log, uint32 seg, int emode,
    				   bool fromArchive);
    static bool XLogPageRead(XLogRecPtr *RecPtr, int emode, bool fetching_ckpt,
    			 bool randAccess);
    static void XLogFileClose(void);
    static bool RestoreArchivedFile(char *path, const char *xlogfname,
    					const char *recovername, off_t expectedSize);
    static void ExecuteRecoveryCommand(char *command, char *commandName,
    					   bool failOnerror);
    static void PreallocXlogFiles(XLogRecPtr endptr);
    static void RemoveOldXlogFiles(uint32 log, uint32 seg, XLogRecPtr endptr);
    static void ValidateXLOGDirectoryStructure(void);
    static void CleanupBackupHistory(void);
    static void UpdateMinRecoveryPoint(XLogRecPtr lsn, bool force);
    static XLogRecord *ReadRecord(XLogRecPtr *RecPtr, int emode, bool fetching_ckpt);
    static bool ValidXLOGHeader(XLogPageHeader hdr, int emode);
    static XLogRecord *ReadCheckpointRecord(XLogRecPtr RecPtr, int whichChkpt);
    static List *readTimeLineHistory(TimeLineID targetTLI);
    static bool existsTimeLineHistory(TimeLineID probeTLI);
    static TimeLineID findNewestTimeLine(TimeLineID startTLI);
    static void writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI,
    					 TimeLineID endTLI,
    					 uint32 endLogId, uint32 endLogSeg);
    static void WriteControlFile(void);
    static void ReadControlFile(void);
    static char *str_time(pg_time_t tnow);
    static bool CheckForStandbyTrigger(void);
    
    #ifdef WAL_DEBUG
    static void xlog_outrec(StringInfo buf, XLogRecord *record);
    #endif
    static void pg_start_backup_callback(int code, Datum arg);
    static bool read_backup_label(XLogRecPtr *checkPointLoc);
    static void rm_redo_error_callback(void *arg);
    static int	get_sync_bit(int method);
    
    
    /*
     * Insert an XLOG record having the specified RMID and info bytes,
     * with the body of the record being the data chunk(s) described by
     * the rdata chain (see xlog.h for notes about rdata).
     *
     * Returns XLOG pointer to end of record (beginning of next record).
     * This can be used as LSN for data pages affected by the logged action.
     * (LSN is the XLOG point up to which the XLOG must be flushed to disk
     * before the data page can be written out.  This implements the basic
     * WAL rule "write the log before the data".)
     *
     * NB: this routine feels free to scribble on the XLogRecData structs,
     * though not on the data they reference.  This is OK since the XLogRecData
     * structs are always just temporaries in the calling code.
     */
    XLogRecPtr
    XLogInsert(RmgrId rmid, uint8 info, XLogRecData *rdata)
    {
    	XLogCtlInsert *Insert = &XLogCtl->Insert;
    	XLogRecord *record;
    	XLogContRecord *contrecord;
    	XLogRecPtr	RecPtr;
    	XLogRecPtr	WriteRqst;
    	uint32		freespace;
    	int			curridx;
    	XLogRecData *rdt;
    	Buffer		dtbuf[XLR_MAX_BKP_BLOCKS];
    	bool		dtbuf_bkp[XLR_MAX_BKP_BLOCKS];
    	BkpBlock	dtbuf_xlg[XLR_MAX_BKP_BLOCKS];
    	XLogRecPtr	dtbuf_lsn[XLR_MAX_BKP_BLOCKS];
    	XLogRecData dtbuf_rdt1[XLR_MAX_BKP_BLOCKS];
    	XLogRecData dtbuf_rdt2[XLR_MAX_BKP_BLOCKS];
    	XLogRecData dtbuf_rdt3[XLR_MAX_BKP_BLOCKS];
    	pg_crc32	rdata_crc;
    	uint32		len,
    				write_len;
    	unsigned	i;
    	bool		updrqst;
    	bool		doPageWrites;
    	bool		isLogSwitch = (rmid == RM_XLOG_ID && info == XLOG_SWITCH);
    
    	/* cross-check on whether we should be here or not */
    	if (!XLogInsertAllowed())
    		elog(ERROR, "cannot make new WAL entries during recovery");
    
    	/* info's high bits are reserved for use by me */
    	if (info & XLR_INFO_MASK)
    		elog(PANIC, "invalid xlog info mask %02X", info);
    
    	TRACE_POSTGRESQL_XLOG_INSERT(rmid, info);
    
    	/*
    	 * In bootstrap mode, we don't actually log anything but XLOG resources;
    	 * return a phony record pointer.
    	 */
    	if (IsBootstrapProcessingMode() && rmid != RM_XLOG_ID)
    	{
    		RecPtr.xlogid = 0;
    		RecPtr.xrecoff = SizeOfXLogLongPHD;		/* start of 1st chkpt record */
    		return RecPtr;
    	}
    
    	/*
    	 * Here we scan the rdata chain, determine which buffers must be backed
    	 * up, and compute the CRC values for the data.  Note that the record
    	 * header isn't added into the CRC initially since we don't know the final
    	 * length or info bits quite yet.  Thus, the CRC will represent the CRC of
    	 * the whole record in the order "rdata, then backup blocks, then record
    	 * header".
    	 *
    	 * We may have to loop back to here if a race condition is detected below.
    	 * We could prevent the race by doing all this work while holding the
    	 * insert lock, but it seems better to avoid doing CRC calculations while
    	 * holding the lock.  This means we have to be careful about modifying the
    	 * rdata chain until we know we aren't going to loop back again.  The only
    	 * change we allow ourselves to make earlier is to set rdt->data = NULL in
    	 * chain items we have decided we will have to back up the whole buffer
    	 * for.  This is OK because we will certainly decide the same thing again
    	 * for those items if we do it over; doing it here saves an extra pass
    	 * over the chain later.
    	 */
    begin:;
    	for (i = 0; i < XLR_MAX_BKP_BLOCKS; i++)
    	{
    		dtbuf[i] = InvalidBuffer;
    		dtbuf_bkp[i] = false;
    	}
    
    	/*
    	 * Decide if we need to do full-page writes in this XLOG record: true if
    	 * full_page_writes is on or we have a PITR request for it.  Since we
    	 * don't yet have the insert lock, forcePageWrites could change under us,
    	 * but we'll recheck it once we have the lock.
    	 */
    	doPageWrites = fullPageWrites || Insert->forcePageWrites;
    
    	INIT_CRC32(rdata_crc);
    	len = 0;
    	for (rdt = rdata;;)
    	{
    		if (rdt->buffer == InvalidBuffer)
    		{
    			/* Simple data, just include it */
    			len += rdt->len;
    			COMP_CRC32(rdata_crc, rdt->data, rdt->len);
    		}
    		else
    		{
    			/* Find info for buffer */
    			for (i = 0; i < XLR_MAX_BKP_BLOCKS; i++)
    			{
    				if (rdt->buffer == dtbuf[i])
    				{
    					/* Buffer already referenced by earlier chain item */
    					if (dtbuf_bkp[i])
    						rdt->data = NULL;
    					else if (rdt->data)
    					{
    						len += rdt->len;
    						COMP_CRC32(rdata_crc, rdt->data, rdt->len);
    					}
    					break;
    				}
    				if (dtbuf[i] == InvalidBuffer)
    				{
    					/* OK, put it in this slot */
    					dtbuf[i] = rdt->buffer;
    					if (XLogCheckBuffer(rdt, doPageWrites,
    										&(dtbuf_lsn[i]), &(dtbuf_xlg[i])))
    					{
    						dtbuf_bkp[i] = true;
    						rdt->data = NULL;
    					}
    					else if (rdt->data)
    					{
    						len += rdt->len;
    						COMP_CRC32(rdata_crc, rdt->data, rdt->len);
    					}
    					break;
    				}
    			}
    			if (i >= XLR_MAX_BKP_BLOCKS)
    				elog(PANIC, "can backup at most %d blocks per xlog record",
    					 XLR_MAX_BKP_BLOCKS);
    		}
    		/* Break out of loop when rdt points to last chain item */
    		if (rdt->next == NULL)
    			break;
    		rdt = rdt->next;
    	}
    
    	/*
    	 * Now add the backup block headers and data into the CRC
    	 */
    	for (i = 0; i < XLR_MAX_BKP_BLOCKS; i++)
    	{
    		if (dtbuf_bkp[i])
    		{
    			BkpBlock   *bkpb = &(dtbuf_xlg[i]);
    			char	   *page;
    
    			COMP_CRC32(rdata_crc,
    					   (char *) bkpb,
    					   sizeof(BkpBlock));
    			page = (char *) BufferGetBlock(dtbuf[i]);
    			if (bkpb->hole_length == 0)
    			{
    				COMP_CRC32(rdata_crc,
    						   page,
    						   BLCKSZ);
    			}
    			else
    			{
    				/* must skip the hole */
    				COMP_CRC32(rdata_crc,
    						   page,
    						   bkpb->hole_offset);
    				COMP_CRC32(rdata_crc,
    						   page + (bkpb->hole_offset + bkpb->hole_length),
    						   BLCKSZ - (bkpb->hole_offset + bkpb->hole_length));
    			}
    		}
    	}
    
    	/*
    	 * NOTE: We disallow len == 0 because it provides a useful bit of extra
    	 * error checking in ReadRecord.  This means that all callers of
    	 * XLogInsert must supply at least some not-in-a-buffer data.  However, we
    	 * make an exception for XLOG SWITCH records because we don't want them to
    	 * ever cross a segment boundary.
    	 */
    	if (len == 0 && !isLogSwitch)
    		elog(PANIC, "invalid xlog record length %u", len);
    
    	START_CRIT_SECTION();
    
    	/* Now wait to get insert lock */
    	LWLockAcquire(WALInsertLock, LW_EXCLUSIVE);
    
    	/*
    	 * Check to see if my RedoRecPtr is out of date.  If so, may have to go
    	 * back and recompute everything.  This can only happen just after a
    	 * checkpoint, so it's better to be slow in this case and fast otherwise.
    	 *
    	 * If we aren't doing full-page writes then RedoRecPtr doesn't actually
    	 * affect the contents of the XLOG record, so we'll update our local copy
    	 * but not force a recomputation.
    	 */
    	if (!XLByteEQ(RedoRecPtr, Insert->RedoRecPtr))
    	{
    		Assert(XLByteLT(RedoRecPtr, Insert->RedoRecPtr));
    		RedoRecPtr = Insert->RedoRecPtr;
    
    		if (doPageWrites)
    		{
    			for (i = 0; i < XLR_MAX_BKP_BLOCKS; i++)
    			{
    				if (dtbuf[i] == InvalidBuffer)
    					continue;
    				if (dtbuf_bkp[i] == false &&
    					XLByteLE(dtbuf_lsn[i], RedoRecPtr))
    				{
    					/*
    					 * Oops, this buffer now needs to be backed up, but we
    					 * didn't think so above.  Start over.
    					 */
    					LWLockRelease(WALInsertLock);
    					END_CRIT_SECTION();
    					goto begin;
    				}
    			}
    		}
    	}
    
    	/*
    	 * Also check to see if forcePageWrites was just turned on; if we weren't
    	 * already doing full-page writes then go back and recompute. (If it was
    	 * just turned off, we could recompute the record without full pages, but
    	 * we choose not to bother.)
    	 */
    	if (Insert->forcePageWrites && !doPageWrites)
    	{
    		/* Oops, must redo it with full-page data */
    		LWLockRelease(WALInsertLock);
    		END_CRIT_SECTION();
    		goto begin;
    	}
    
    	/*
    	 * Make additional rdata chain entries for the backup blocks, so that we
    	 * don't need to special-case them in the write loop.  Note that we have
    	 * now irrevocably changed the input rdata chain.  At the exit of this
    	 * loop, write_len includes the backup block data.
    	 *
    	 * Also set the appropriate info bits to show which buffers were backed
    	 * up. The i'th XLR_SET_BKP_BLOCK bit corresponds to the i'th distinct
    	 * buffer value (ignoring InvalidBuffer) appearing in the rdata chain.
    	 */
    	write_len = len;
    	for (i = 0; i < XLR_MAX_BKP_BLOCKS; i++)
    	{
    		BkpBlock   *bkpb;
    		char	   *page;
    
    		if (!dtbuf_bkp[i])
    			continue;
    
    		info |= XLR_SET_BKP_BLOCK(i);
    
    		bkpb = &(dtbuf_xlg[i]);
    		page = (char *) BufferGetBlock(dtbuf[i]);
    
    		rdt->next = &(dtbuf_rdt1[i]);
    		rdt = rdt->next;
    
    		rdt->data = (char *) bkpb;
    		rdt->len = sizeof(BkpBlock);
    		write_len += sizeof(BkpBlock);
    
    		rdt->next = &(dtbuf_rdt2[i]);
    		rdt = rdt->next;
    
    		if (bkpb->hole_length == 0)
    		{
    			rdt->data = page;
    			rdt->len = BLCKSZ;
    			write_len += BLCKSZ;
    			rdt->next = NULL;
    		}
    		else
    		{
    			/* must skip the hole */
    			rdt->data = page;
    			rdt->len = bkpb->hole_offset;
    			write_len += bkpb->hole_offset;
    
    			rdt->next = &(dtbuf_rdt3[i]);
    			rdt = rdt->next;
    
    			rdt->data = page + (bkpb->hole_offset + bkpb->hole_length);
    			rdt->len = BLCKSZ - (bkpb->hole_offset + bkpb->hole_length);
    			write_len += rdt->len;
    			rdt->next = NULL;
    		}
    	}
    
    	/*
    	 * If we backed up any full blocks and online backup is not in progress,
    	 * mark the backup blocks as removable.  This allows the WAL archiver to
    	 * know whether it is safe to compress archived WAL data by transforming
    	 * full-block records into the non-full-block format.
    	 *
    	 * Note: we could just set the flag whenever !forcePageWrites, but
    	 * defining it like this leaves the info bit free for some potential other
    	 * use in records without any backup blocks.
    	 */
    	if ((info & XLR_BKP_BLOCK_MASK) && !Insert->forcePageWrites)
    		info |= XLR_BKP_REMOVABLE;
    
    	/*
    	 * If there isn't enough space on the current XLOG page for a record
    	 * header, advance to the next page (leaving the unused space as zeroes).
    	 */
    	updrqst = false;
    	freespace = INSERT_FREESPACE(Insert);
    	if (freespace < SizeOfXLogRecord)
    	{
    		updrqst = AdvanceXLInsertBuffer(false);
    		freespace = INSERT_FREESPACE(Insert);
    	}
    
    	/* Compute record's XLOG location */
    	curridx = Insert->curridx;
    	INSERT_RECPTR(RecPtr, Insert, curridx);
    
    	/*
    	 * If the record is an XLOG_SWITCH, and we are exactly at the start of a
    	 * segment, we need not insert it (and don't want to because we'd like
    	 * consecutive switch requests to be no-ops).  Instead, make sure
    	 * everything is written and flushed through the end of the prior segment,
    	 * and return the prior segment's end address.
    	 */
    	if (isLogSwitch &&
    		(RecPtr.xrecoff % XLogSegSize) == SizeOfXLogLongPHD)
    	{
    		/* We can release insert lock immediately */
    		LWLockRelease(WALInsertLock);
    
    		RecPtr.xrecoff -= SizeOfXLogLongPHD;
    		if (RecPtr.xrecoff == 0)
    		{
    			/* crossing a logid boundary */
    			RecPtr.xlogid -= 1;
    			RecPtr.xrecoff = XLogFileSize;
    		}
    
    		LWLockAcquire(WALWriteLock, LW_EXCLUSIVE);
    		LogwrtResult = XLogCtl->Write.LogwrtResult;
    		if (!XLByteLE(RecPtr, LogwrtResult.Flush))
    		{
    			XLogwrtRqst FlushRqst;
    
    			FlushRqst.Write = RecPtr;
    			FlushRqst.Flush = RecPtr;
    			XLogWrite(FlushRqst, false, false);
    		}
    		LWLockRelease(WALWriteLock);
    
    		END_CRIT_SECTION();
    
    		return RecPtr;
    	}
    
    	/* Insert record header */
    
    	record = (XLogRecord *) Insert->currpos;
    	record->xl_prev = Insert->PrevRecord;
    	record->xl_xid = GetCurrentTransactionIdIfAny();
    	record->xl_tot_len = SizeOfXLogRecord + write_len;
    	record->xl_len = len;		/* doesn't include backup blocks */
    	record->xl_info = info;
    	record->xl_rmid = rmid;
    
    	/* Now we can finish computing the record's CRC */
    	COMP_CRC32(rdata_crc, (char *) record + sizeof(pg_crc32),
    			   SizeOfXLogRecord - sizeof(pg_crc32));
    	FIN_CRC32(rdata_crc);
    	record->xl_crc = rdata_crc;
    
    #ifdef WAL_DEBUG
    	if (XLOG_DEBUG)
    	{
    		StringInfoData buf;
    
    		initStringInfo(&buf);
    		appendStringInfo(&buf, "INSERT @ %X/%X: ",
    						 RecPtr.xlogid, RecPtr.xrecoff);
    		xlog_outrec(&buf, record);
    		if (rdata->data != NULL)
    		{
    			appendStringInfo(&buf, " - ");
    			RmgrTable[record->xl_rmid].rm_desc(&buf, record->xl_info, rdata->data);
    		}
    		elog(LOG, "%s", buf.data);
    		pfree(buf.data);
    	}
    #endif
    
    	/* Record begin of record in appropriate places */
    	ProcLastRecPtr = RecPtr;
    	Insert->PrevRecord = RecPtr;
    
    	Insert->currpos += SizeOfXLogRecord;
    	freespace -= SizeOfXLogRecord;
    
    	/*
    	 * Append the data, including backup blocks if any
    	 */
    	while (write_len)
    	{
    		while (rdata->data == NULL)
    			rdata = rdata->next;
    
    		if (freespace > 0)
    		{
    			if (rdata->len > freespace)
    			{
    				memcpy(Insert->currpos, rdata->data, freespace);
    				rdata->data += freespace;
    				rdata->len -= freespace;
    				write_len -= freespace;
    			}
    			else
    			{
    				memcpy(Insert->currpos, rdata->data, rdata->len);
    				freespace -= rdata->len;
    				write_len -= rdata->len;
    				Insert->currpos += rdata->len;
    				rdata = rdata->next;
    				continue;
    			}
    		}
    
    		/* Use next buffer */
    		updrqst = AdvanceXLInsertBuffer(false);
    		curridx = Insert->curridx;
    		/* Insert cont-record header */
    		Insert->currpage->xlp_info |= XLP_FIRST_IS_CONTRECORD;
    		contrecord = (XLogContRecord *) Insert->currpos;
    		contrecord->xl_rem_len = write_len;
    		Insert->currpos += SizeOfXLogContRecord;
    		freespace = INSERT_FREESPACE(Insert);
    	}
    
    	/* Ensure next record will be properly aligned */
    	Insert->currpos = (char *) Insert->currpage +
    		MAXALIGN(Insert->currpos - (char *) Insert->currpage);
    	freespace = INSERT_FREESPACE(Insert);
    
    	/*
    	 * The recptr I return is the beginning of the *next* record. This will be
    	 * stored as LSN for changed data pages...
    	 */
    	INSERT_RECPTR(RecPtr, Insert, curridx);
    
    	/*
    	 * If the record is an XLOG_SWITCH, we must now write and flush all the
    	 * existing data, and then forcibly advance to the start of the next
    	 * segment.  It's not good to do this I/O while holding the insert lock,
    	 * but there seems too much risk of confusion if we try to release the
    	 * lock sooner.  Fortunately xlog switch needn't be a high-performance
    	 * operation anyway...
    	 */
    	if (isLogSwitch)
    	{
    		XLogCtlWrite *Write = &XLogCtl->Write;
    		XLogwrtRqst FlushRqst;
    		XLogRecPtr	OldSegEnd;
    
    		TRACE_POSTGRESQL_XLOG_SWITCH();
    
    		LWLockAcquire(WALWriteLock, LW_EXCLUSIVE);
    
    		/*
    		 * Flush through the end of the page containing XLOG_SWITCH, and
    		 * perform end-of-segment actions (eg, notifying archiver).
    		 */
    		WriteRqst = XLogCtl->xlblocks[curridx];
    		FlushRqst.Write = WriteRqst;
    		FlushRqst.Flush = WriteRqst;
    		XLogWrite(FlushRqst, false, true);
    
    		/* Set up the next buffer as first page of next segment */
    		/* Note: AdvanceXLInsertBuffer cannot need to do I/O here */
    		(void) AdvanceXLInsertBuffer(true);
    
    		/* There should be no unwritten data */
    		curridx = Insert->curridx;
    		Assert(curridx == Write->curridx);
    
    		/* Compute end address of old segment */
    		OldSegEnd = XLogCtl->xlblocks[curridx];
    		OldSegEnd.xrecoff -= XLOG_BLCKSZ;
    		if (OldSegEnd.xrecoff == 0)
    		{
    			/* crossing a logid boundary */
    			OldSegEnd.xlogid -= 1;
    			OldSegEnd.xrecoff = XLogFileSize;
    		}
    
    		/* Make it look like we've written and synced all of old segment */
    		LogwrtResult.Write = OldSegEnd;
    		LogwrtResult.Flush = OldSegEnd;
    
    		/*
    		 * Update shared-memory status --- this code should match XLogWrite
    		 */
    		{
    			/* use volatile pointer to prevent code rearrangement */
    			volatile XLogCtlData *xlogctl = XLogCtl;
    
    			SpinLockAcquire(&xlogctl->info_lck);
    			xlogctl->LogwrtResult = LogwrtResult;
    			if (XLByteLT(xlogctl->LogwrtRqst.Write, LogwrtResult.Write))
    				xlogctl->LogwrtRqst.Write = LogwrtResult.Write;
    			if (XLByteLT(xlogctl->LogwrtRqst.Flush, LogwrtResult.Flush))
    				xlogctl->LogwrtRqst.Flush = LogwrtResult.Flush;
    			SpinLockRelease(&xlogctl->info_lck);
    		}
    
    		Write->LogwrtResult = LogwrtResult;
    
    		LWLockRelease(WALWriteLock);
    
    		updrqst = false;		/* done already */
    	}
    	else
    	{
    		/* normal case, ie not xlog switch */
    
    		/* Need to update shared LogwrtRqst if some block was filled up */
    		if (freespace < SizeOfXLogRecord)
    		{
    			/* curridx is filled and available for writing out */
    			updrqst = true;
    		}
    		else
    		{
    			/* if updrqst already set, write through end of previous buf */
    			curridx = PrevBufIdx(curridx);
    		}
    		WriteRqst = XLogCtl->xlblocks[curridx];
    	}
    
    	LWLockRelease(WALInsertLock);
    
    	if (updrqst)
    	{
    		/* use volatile pointer to prevent code rearrangement */
    		volatile XLogCtlData *xlogctl = XLogCtl;
    
    		SpinLockAcquire(&xlogctl->info_lck);
    		/* advance global request to include new block(s) */
    		if (XLByteLT(xlogctl->LogwrtRqst.Write, WriteRqst))
    			xlogctl->LogwrtRqst.Write = WriteRqst;
    		/* update local result copy while I have the chance */
    		LogwrtResult = xlogctl->LogwrtResult;
    		SpinLockRelease(&xlogctl->info_lck);
    	}
    
    	XactLastRecEnd = RecPtr;
    
    	END_CRIT_SECTION();
    
    	return RecPtr;
    }
    
    /*
     * Determine whether the buffer referenced by an XLogRecData item has to
     * be backed up, and if so fill a BkpBlock struct for it.  In any case
     * save the buffer's LSN at *lsn.
     */
    static bool
    XLogCheckBuffer(XLogRecData *rdata, bool doPageWrites,
    				XLogRecPtr *lsn, BkpBlock *bkpb)
    {
    	Page		page;
    
    	page = BufferGetPage(rdata->buffer);
    
    	/*
    	 * XXX We assume page LSN is first data on *every* page that can be passed
    	 * to XLogInsert, whether it otherwise has the standard page layout or
    	 * not.
    	 */
    	*lsn = PageGetLSN(page);
    
    	if (doPageWrites &&
    		XLByteLE(PageGetLSN(page), RedoRecPtr))
    	{
    		/*
    		 * The page needs to be backed up, so set up *bkpb
    		 */
    		BufferGetTag(rdata->buffer, &bkpb->node, &bkpb->fork, &bkpb->block);
    
    		if (rdata->buffer_std)
    		{
    			/* Assume we can omit data between pd_lower and pd_upper */
    			uint16		lower = ((PageHeader) page)->pd_lower;
    			uint16		upper = ((PageHeader) page)->pd_upper;
    
    			if (lower >= SizeOfPageHeaderData &&
    				upper > lower &&
    				upper <= BLCKSZ)
    			{
    				bkpb->hole_offset = lower;
    				bkpb->hole_length = upper - lower;
    			}
    			else
    			{
    				/* No "hole" to compress out */
    				bkpb->hole_offset = 0;
    				bkpb->hole_length = 0;
    			}
    		}
    		else
    		{
    			/* Not a standard page header, don't try to eliminate "hole" */
    			bkpb->hole_offset = 0;
    			bkpb->hole_length = 0;
    		}
    
    		return true;			/* buffer requires backup */
    	}
    
    	return false;				/* buffer does not need to be backed up */
    }
    
    /*
     * XLogArchiveNotify
     *
     * Create an archive notification file
     *
     * The name of the notification file is the message that will be picked up
     * by the archiver, e.g. we write 0000000100000001000000C6.ready
     * and the archiver then knows to archive XLOGDIR/0000000100000001000000C6,
     * then when complete, rename it to 0000000100000001000000C6.done
     */
    static void
    XLogArchiveNotify(const char *xlog)
    {
    	char		archiveStatusPath[MAXPGPATH];
    	FILE	   *fd;
    
    	/* insert an otherwise empty file called <XLOG>.ready */
    	StatusFilePath(archiveStatusPath, xlog, ".ready");
    	fd = AllocateFile(archiveStatusPath, "w");
    	if (fd == NULL)
    	{
    		ereport(LOG,
    				(errcode_for_file_access(),
    				 errmsg("could not create archive status file \"%s\": %m",
    						archiveStatusPath)));
    		return;
    	}
    	if (FreeFile(fd))
    	{
    		ereport(LOG,
    				(errcode_for_file_access(),
    				 errmsg("could not write archive status file \"%s\": %m",
    						archiveStatusPath)));
    		return;
    	}
    
    	/* Notify archiver that it's got something to do */
    	if (IsUnderPostmaster)
    		SendPostmasterSignal(PMSIGNAL_WAKEN_ARCHIVER);
    }
    
    /*
     * Convenience routine to notify using log/seg representation of filename
     */
    static void
    XLogArchiveNotifySeg(uint32 log, uint32 seg)
    {
    	char		xlog[MAXFNAMELEN];
    
    	XLogFileName(xlog, ThisTimeLineID, log, seg);
    	XLogArchiveNotify(xlog);
    }
    
    /*
     * XLogArchiveCheckDone
     *
     * This is called when we are ready to delete or recycle an old XLOG segment
     * file or backup history file.  If it is okay to delete it then return true.
     * If it is not time to delete it, make sure a .ready file exists, and return
     * false.
     *
     * If <XLOG>.done exists, then return true; else if <XLOG>.ready exists,
     * then return false; else create <XLOG>.ready and return false.
     *
     * The reason we do things this way is so that if the original attempt to
     * create <XLOG>.ready fails, we'll retry during subsequent checkpoints.
     */
    static bool
    XLogArchiveCheckDone(const char *xlog)
    {
    	char		archiveStatusPath[MAXPGPATH];
    	struct stat stat_buf;
    
    	/* Always deletable if archiving is off */
    	if (!XLogArchivingActive())
    		return true;
    
    	/* First check for .done --- this means archiver is done with it */
    	StatusFilePath(archiveStatusPath, xlog, ".done");
    	if (stat(archiveStatusPath, &stat_buf) == 0)
    		return true;
    
    	/* check for .ready --- this means archiver is still busy with it */
    	StatusFilePath(archiveStatusPath, xlog, ".ready");
    	if (stat(archiveStatusPath, &stat_buf) == 0)
    		return false;
    
    	/* Race condition --- maybe archiver just finished, so recheck */
    	StatusFilePath(archiveStatusPath, xlog, ".done");
    	if (stat(archiveStatusPath, &stat_buf) == 0)
    		return true;
    
    	/* Retry creation of the .ready file */
    	XLogArchiveNotify(xlog);
    	return false;
    }
    
    /*
     * XLogArchiveIsBusy
     *
     * Check to see if an XLOG segment file is still unarchived.
     * This is almost but not quite the inverse of XLogArchiveCheckDone: in
     * the first place we aren't chartered to recreate the .ready file, and
     * in the second place we should consider that if the file is already gone
     * then it's not busy.  (This check is needed to handle the race condition
     * that a checkpoint already deleted the no-longer-needed file.)
     */
    static bool
    XLogArchiveIsBusy(const char *xlog)
    {
    	char		archiveStatusPath[MAXPGPATH];
    	struct stat stat_buf;
    
    	/* First check for .done --- this means archiver is done with it */
    	StatusFilePath(archiveStatusPath, xlog, ".done");
    	if (stat(archiveStatusPath, &stat_buf) == 0)
    		return false;
    
    	/* check for .ready --- this means archiver is still busy with it */
    	StatusFilePath(archiveStatusPath, xlog, ".ready");
    	if (stat(archiveStatusPath, &stat_buf) == 0)
    		return true;
    
    	/* Race condition --- maybe archiver just finished, so recheck */
    	StatusFilePath(archiveStatusPath, xlog, ".done");
    	if (stat(archiveStatusPath, &stat_buf) == 0)
    		return false;
    
    	/*
    	 * Check to see if the WAL file has been removed by checkpoint, which
    	 * implies it has already been archived, and explains why we can't see a
    	 * status file for it.
    	 */
    	snprintf(archiveStatusPath, MAXPGPATH, XLOGDIR "/%s", xlog);
    	if (stat(archiveStatusPath, &stat_buf) != 0 &&
    		errno == ENOENT)
    		return false;
    
    	return true;
    }
    
    /*
     * XLogArchiveCleanup
     *
     * Cleanup archive notification file(s) for a particular xlog segment
     */
    static void
    XLogArchiveCleanup(const char *xlog)
    {
    	char		archiveStatusPath[MAXPGPATH];
    
    	/* Remove the .done file */
    	StatusFilePath(archiveStatusPath, xlog, ".done");
    	unlink(archiveStatusPath);
    	/* should we complain about failure? */
    
    	/* Remove the .ready file if present --- normally it shouldn't be */
    	StatusFilePath(archiveStatusPath, xlog, ".ready");
    	unlink(archiveStatusPath);
    	/* should we complain about failure? */
    }
    
    /*
     * Advance the Insert state to the next buffer page, writing out the next
     * buffer if it still contains unwritten data.
     *
     * If new_segment is TRUE then we set up the next buffer page as the first
     * page of the next xlog segment file, possibly but not usually the next
     * consecutive file page.
     *
     * The global LogwrtRqst.Write pointer needs to be advanced to include the
     * just-filled page.  If we can do this for free (without an extra lock),
     * we do so here.  Otherwise the caller must do it.  We return TRUE if the
     * request update still needs to be done, FALSE if we did it internally.
     *
     * Must be called with WALInsertLock held.
     */
    static bool
    AdvanceXLInsertBuffer(bool new_segment)
    {
    	XLogCtlInsert *Insert = &XLogCtl->Insert;
    	XLogCtlWrite *Write = &XLogCtl->Write;
    	int			nextidx = NextBufIdx(Insert->curridx);
    	bool		update_needed = true;
    	XLogRecPtr	OldPageRqstPtr;
    	XLogwrtRqst WriteRqst;
    	XLogRecPtr	NewPageEndPtr;
    	XLogPageHeader NewPage;
    
    	/* Use Insert->LogwrtResult copy if it's more fresh */
    	if (XLByteLT(LogwrtResult.Write, Insert->LogwrtResult.Write))
    		LogwrtResult = Insert->LogwrtResult;
    
    	/*
    	 * Get ending-offset of the buffer page we need to replace (this may be
    	 * zero if the buffer hasn't been used yet).  Fall through if it's already
    	 * written out.
    	 */
    	OldPageRqstPtr = XLogCtl->xlblocks[nextidx];
    	if (!XLByteLE(OldPageRqstPtr, LogwrtResult.Write))
    	{
    		/* nope, got work to do... */
    		XLogRecPtr	FinishedPageRqstPtr;
    
    		FinishedPageRqstPtr = XLogCtl->xlblocks[Insert->curridx];
    
    		/* Before waiting, get info_lck and update LogwrtResult */
    		{
    			/* use volatile pointer to prevent code rearrangement */
    			volatile XLogCtlData *xlogctl = XLogCtl;
    
    			SpinLockAcquire(&xlogctl->info_lck);
    			if (XLByteLT(xlogctl->LogwrtRqst.Write, FinishedPageRqstPtr))
    				xlogctl->LogwrtRqst.Write = FinishedPageRqstPtr;
    			LogwrtResult = xlogctl->LogwrtResult;
    			SpinLockRelease(&xlogctl->info_lck);
    		}
    
    		update_needed = false;	/* Did the shared-request update */
    
    		if (XLByteLE(OldPageRqstPtr, LogwrtResult.Write))
    		{
    			/* OK, someone wrote it already */
    			Insert->LogwrtResult = LogwrtResult;
    		}
    		else
    		{
    			/* Must acquire write lock */
    			LWLockAcquire(WALWriteLock, LW_EXCLUSIVE);
    			LogwrtResult = Write->LogwrtResult;
    			if (XLByteLE(OldPageRqstPtr, LogwrtResult.Write))
    			{
    				/* OK, someone wrote it already */
    				LWLockRelease(WALWriteLock);
    				Insert->LogwrtResult = LogwrtResult;
    			}
    			else
    			{
    				/*
    				 * Have to write buffers while holding insert lock. This is
    				 * not good, so only write as much as we absolutely must.
    				 */
    				TRACE_POSTGRESQL_WAL_BUFFER_WRITE_DIRTY_START();
    				WriteRqst.Write = OldPageRqstPtr;
    				WriteRqst.Flush.xlogid = 0;
    				WriteRqst.Flush.xrecoff = 0;
    				XLogWrite(WriteRqst, false, false);
    				LWLockRelease(WALWriteLock);
    				Insert->LogwrtResult = LogwrtResult;
    				TRACE_POSTGRESQL_WAL_BUFFER_WRITE_DIRTY_DONE();
    			}
    		}
    	}
    
    	/*
    	 * Now the next buffer slot is free and we can set it up to be the next
    	 * output page.
    	 */
    	NewPageEndPtr = XLogCtl->xlblocks[Insert->curridx];
    
    	if (new_segment)
    	{
    		/* force it to a segment start point */
    		NewPageEndPtr.xrecoff += XLogSegSize - 1;
    		NewPageEndPtr.xrecoff -= NewPageEndPtr.xrecoff % XLogSegSize;
    	}
    
    	if (NewPageEndPtr.xrecoff >= XLogFileSize)
    	{
    		/* crossing a logid boundary */
    		NewPageEndPtr.xlogid += 1;
    		NewPageEndPtr.xrecoff = XLOG_BLCKSZ;
    	}
    	else
    		NewPageEndPtr.xrecoff += XLOG_BLCKSZ;
    	XLogCtl->xlblocks[nextidx] = NewPageEndPtr;
    	NewPage = (XLogPageHeader) (XLogCtl->pages + nextidx * (Size) XLOG_BLCKSZ);
    
    	Insert->curridx = nextidx;
    	Insert->currpage = NewPage;
    
    	Insert->currpos = ((char *) NewPage) +SizeOfXLogShortPHD;
    
    	/*
    	 * Be sure to re-zero the buffer so that bytes beyond what we've written
    	 * will look like zeroes and not valid XLOG records...
    	 */
    	MemSet((char *) NewPage, 0, XLOG_BLCKSZ);
    
    	/*
    	 * Fill the new page's header
    	 */
    	NewPage   ->xlp_magic = XLOG_PAGE_MAGIC;
    
    	/* NewPage->xlp_info = 0; */	/* done by memset */
    	NewPage   ->xlp_tli = ThisTimeLineID;
    	NewPage   ->xlp_pageaddr.xlogid = NewPageEndPtr.xlogid;
    	NewPage   ->xlp_pageaddr.xrecoff = NewPageEndPtr.xrecoff - XLOG_BLCKSZ;
    
    	/*
    	 * If first page of an XLOG segment file, make it a long header.
    	 */
    	if ((NewPage->xlp_pageaddr.xrecoff % XLogSegSize) == 0)
    	{
    		XLogLongPageHeader NewLongPage = (XLogLongPageHeader) NewPage;
    
    		NewLongPage->xlp_sysid = ControlFile->system_identifier;
    		NewLongPage->xlp_seg_size = XLogSegSize;
    		NewLongPage->xlp_xlog_blcksz = XLOG_BLCKSZ;
    		NewPage   ->xlp_info |= XLP_LONG_HEADER;
    
    		Insert->currpos = ((char *) NewPage) +SizeOfXLogLongPHD;
    	}
    
    	return update_needed;
    }
    
    /*
     * Check whether we've consumed enough xlog space that a checkpoint is needed.
     *
     * Caller must have just finished filling the open log file (so that
     * openLogId/openLogSeg are valid).  We measure the distance from RedoRecPtr
     * to the open log file and see if that exceeds CheckPointSegments.
     *
     * Note: it is caller's responsibility that RedoRecPtr is up-to-date.
     */
    static bool
    XLogCheckpointNeeded(void)
    {
    	/*
    	 * A straight computation of segment number could overflow 32 bits. Rather
    	 * than assuming we have working 64-bit arithmetic, we compare the
    	 * highest-order bits separately, and force a checkpoint immediately when
    	 * they change.
    	 */
    	uint32		old_segno,
    				new_segno;
    	uint32		old_highbits,
    				new_highbits;
    
    	old_segno = (RedoRecPtr.xlogid % XLogSegSize) * XLogSegsPerFile +
    		(RedoRecPtr.xrecoff / XLogSegSize);
    	old_highbits = RedoRecPtr.xlogid / XLogSegSize;
    	new_segno = (openLogId % XLogSegSize) * XLogSegsPerFile + openLogSeg;
    	new_highbits = openLogId / XLogSegSize;
    	if (new_highbits != old_highbits ||
    		new_segno >= old_segno + (uint32) (CheckPointSegments - 1))
    		return true;
    	return false;
    }
    
    /*
     * Write and/or fsync the log at least as far as WriteRqst indicates.
     *
     * If flexible == TRUE, we don't have to write as far as WriteRqst, but
     * may stop at any convenient boundary (such as a cache or logfile boundary).
     * This option allows us to avoid uselessly issuing multiple writes when a
     * single one would do.
     *
     * If xlog_switch == TRUE, we are intending an xlog segment switch, so
     * perform end-of-segment actions after writing the last page, even if
     * it's not physically the end of its segment.  (NB: this will work properly
     * only if caller specifies WriteRqst == page-end and flexible == false,
     * and there is some data to write.)
     *
     * Must be called with WALWriteLock held.
     */
    static void
    XLogWrite(XLogwrtRqst WriteRqst, bool flexible, bool xlog_switch)
    {
    	XLogCtlWrite *Write = &XLogCtl->Write;
    	bool		ispartialpage;
    	bool		last_iteration;
    	bool		finishing_seg;
    	bool		use_existent;
    	int			curridx;
    	int			npages;
    	int			startidx;
    	uint32		startoffset;
    
    	/* We should always be inside a critical section here */
    	Assert(CritSectionCount > 0);
    
    	/*
    	 * Update local LogwrtResult (caller probably did this already, but...)
    	 */
    	LogwrtResult = Write->LogwrtResult;
    
    	/*
    	 * Since successive pages in the xlog cache are consecutively allocated,
    	 * we can usually gather multiple pages together and issue just one
    	 * write() call.  npages is the number of pages we have determined can be
    	 * written together; startidx is the cache block index of the first one,
    	 * and startoffset is the file offset at which it should go. The latter
    	 * two variables are only valid when npages > 0, but we must initialize
    	 * all of them to keep the compiler quiet.
    	 */
    	npages = 0;
    	startidx = 0;
    	startoffset = 0;
    
    	/*
    	 * Within the loop, curridx is the cache block index of the page to
    	 * consider writing.  We advance Write->curridx only after successfully
    	 * writing pages.  (Right now, this refinement is useless since we are
    	 * going to PANIC if any error occurs anyway; but someday it may come in
    	 * useful.)
    	 */
    	curridx = Write->curridx;
    
    	while (XLByteLT(LogwrtResult.Write, WriteRqst.Write))
    	{
    		/*
    		 * Make sure we're not ahead of the insert process.  This could happen
    		 * if we're passed a bogus WriteRqst.Write that is past the end of the
    		 * last page that's been initialized by AdvanceXLInsertBuffer.
    		 */
    		if (!XLByteLT(LogwrtResult.Write, XLogCtl->xlblocks[curridx]))
    			elog(PANIC, "xlog write request %X/%X is past end of log %X/%X",
    				 LogwrtResult.Write.xlogid, LogwrtResult.Write.xrecoff,
    				 XLogCtl->xlblocks[curridx].xlogid,
    				 XLogCtl->xlblocks[curridx].xrecoff);
    
    		/* Advance LogwrtResult.Write to end of current buffer page */
    		LogwrtResult.Write = XLogCtl->xlblocks[curridx];
    		ispartialpage = XLByteLT(WriteRqst.Write, LogwrtResult.Write);
    
    		if (!XLByteInPrevSeg(LogwrtResult.Write, openLogId, openLogSeg))
    		{
    			/*
    			 * Switch to new logfile segment.  We cannot have any pending
    			 * pages here (since we dump what we have at segment end).
    			 */
    			Assert(npages == 0);
    			if (openLogFile >= 0)
    				XLogFileClose();
    			XLByteToPrevSeg(LogwrtResult.Write, openLogId, openLogSeg);
    
    			/* create/use new log file */
    			use_existent = true;
    			openLogFile = XLogFileInit(openLogId, openLogSeg,
    									   &use_existent, true);
    			openLogOff = 0;
    		}
    
    		/* Make sure we have the current logfile open */
    		if (openLogFile < 0)
    		{
    			XLByteToPrevSeg(LogwrtResult.Write, openLogId, openLogSeg);
    			openLogFile = XLogFileOpen(openLogId, openLogSeg);
    			openLogOff = 0;
    		}
    
    		/* Add current page to the set of pending pages-to-dump */
    		if (npages == 0)
    		{
    			/* first of group */
    			startidx = curridx;
    			startoffset = (LogwrtResult.Write.xrecoff - XLOG_BLCKSZ) % XLogSegSize;
    		}
    		npages++;
    
    		/*
    		 * Dump the set if this will be the last loop iteration, or if we are
    		 * at the last page of the cache area (since the next page won't be
    		 * contiguous in memory), or if we are at the end of the logfile
    		 * segment.
    		 */
    		last_iteration = !XLByteLT(LogwrtResult.Write, WriteRqst.Write);
    
    		finishing_seg = !ispartialpage &&
    			(startoffset + npages * XLOG_BLCKSZ) >= XLogSegSize;
    
    		if (last_iteration ||
    			curridx == XLogCtl->XLogCacheBlck ||
    			finishing_seg)
    		{
    			char	   *from;
    			Size		nbytes;
    
    			/* Need to seek in the file? */
    			if (openLogOff != startoffset)
    			{
    				if (lseek(openLogFile, (off_t) startoffset, SEEK_SET) < 0)
    					ereport(PANIC,
    							(errcode_for_file_access(),
    							 errmsg("could not seek in log file %u, "
    									"segment %u to offset %u: %m",
    									openLogId, openLogSeg, startoffset)));
    				openLogOff = startoffset;
    			}
    
    			/* OK to write the page(s) */
    			from = XLogCtl->pages + startidx * (Size) XLOG_BLCKSZ;
    			nbytes = npages * (Size) XLOG_BLCKSZ;
    			errno = 0;
    			if (write(openLogFile, from, nbytes) != nbytes)
    			{
    				/* if write didn't set errno, assume no disk space */
    				if (errno == 0)
    					errno = ENOSPC;
    				ereport(PANIC,
    						(errcode_for_file_access(),
    						 errmsg("could not write to log file %u, segment %u "
    								"at offset %u, length %lu: %m",
    								openLogId, openLogSeg,
    								openLogOff, (unsigned long) nbytes)));
    			}
    
    			/* Update state for write */
    			openLogOff += nbytes;
    			Write->curridx = ispartialpage ? curridx : NextBufIdx(curridx);
    			npages = 0;
    
    			/*
    			 * If we just wrote the whole last page of a logfile segment,
    			 * fsync the segment immediately.  This avoids having to go back
    			 * and re-open prior segments when an fsync request comes along
    			 * later. Doing it here ensures that one and only one backend will
    			 * perform this fsync.
    			 *
    			 * We also do this if this is the last page written for an xlog
    			 * switch.
    			 *
    			 * This is also the right place to notify the Archiver that the
    			 * segment is ready to copy to archival storage, and to update the
    			 * timer for archive_timeout, and to signal for a checkpoint if
    			 * too many logfile segments have been used since the last
    			 * checkpoint.
    			 */
    			if (finishing_seg || (xlog_switch && last_iteration))
    			{
    				issue_xlog_fsync(openLogFile, openLogId, openLogSeg);
    				LogwrtResult.Flush = LogwrtResult.Write;		/* end of page */
    
    				if (XLogArchivingActive())
    					XLogArchiveNotifySeg(openLogId, openLogSeg);
    
    				Write->lastSegSwitchTime = (pg_time_t) time(NULL);
    
    				/*
    				 * Signal bgwriter to start a checkpoint if we've consumed too
    				 * much xlog since the last one.  For speed, we first check
    				 * using the local copy of RedoRecPtr, which might be out of
    				 * date; if it looks like a checkpoint is needed, forcibly
    				 * update RedoRecPtr and recheck.
    				 */
    				if (IsUnderPostmaster &&
    					XLogCheckpointNeeded())
    				{
    					(void) GetRedoRecPtr();
    					if (XLogCheckpointNeeded())
    						RequestCheckpoint(CHECKPOINT_CAUSE_XLOG);
    				}
    			}
    		}
    
    		if (ispartialpage)
    		{
    			/* Only asked to write a partial page */
    			LogwrtResult.Write = WriteRqst.Write;
    			break;
    		}
    		curridx = NextBufIdx(curridx);
    
    		/* If flexible, break out of loop as soon as we wrote something */
    		if (flexible && npages == 0)
    			break;
    	}
    
    	Assert(npages == 0);
    	Assert(curridx == Write->curridx);
    
    	/*
    	 * If asked to flush, do so
    	 */
    	if (XLByteLT(LogwrtResult.Flush, WriteRqst.Flush) &&
    		XLByteLT(LogwrtResult.Flush, LogwrtResult.Write))
    	{
    		/*
    		 * Could get here without iterating above loop, in which case we might
    		 * have no open file or the wrong one.	However, we do not need to
    		 * fsync more than one file.
    		 */
    		if (sync_method != SYNC_METHOD_OPEN &&
    			sync_method != SYNC_METHOD_OPEN_DSYNC)
    		{
    			if (openLogFile >= 0 &&
    				!XLByteInPrevSeg(LogwrtResult.Write, openLogId, openLogSeg))
    				XLogFileClose();
    			if (openLogFile < 0)
    			{
    				XLByteToPrevSeg(LogwrtResult.Write, openLogId, openLogSeg);
    				openLogFile = XLogFileOpen(openLogId, openLogSeg);
    				openLogOff = 0;
    			}
    			issue_xlog_fsync(openLogFile, openLogId, openLogSeg);
    		}
    		LogwrtResult.Flush = LogwrtResult.Write;
    	}
    
    	/*
    	 * Update shared-memory status
    	 *
    	 * We make sure that the shared 'request' values do not fall behind the
    	 * 'result' values.  This is not absolutely essential, but it saves some
    	 * code in a couple of places.
    	 */
    	{
    		/* use volatile pointer to prevent code rearrangement */
    		volatile XLogCtlData *xlogctl = XLogCtl;
    
    		SpinLockAcquire(&xlogctl->info_lck);
    		xlogctl->LogwrtResult = LogwrtResult;
    		if (XLByteLT(xlogctl->LogwrtRqst.Write, LogwrtResult.Write))
    			xlogctl->LogwrtRqst.Write = LogwrtResult.Write;
    		if (XLByteLT(xlogctl->LogwrtRqst.Flush, LogwrtResult.Flush))
    			xlogctl->LogwrtRqst.Flush = LogwrtResult.Flush;
    		SpinLockRelease(&xlogctl->info_lck);
    	}
    
    	Write->LogwrtResult = LogwrtResult;
    }
    
    /*
     * Record the LSN for an asynchronous transaction commit.
     * (This should not be called for aborts, nor for synchronous commits.)
     */
    void
    XLogSetAsyncCommitLSN(XLogRecPtr asyncCommitLSN)
    {
    	/* use volatile pointer to prevent code rearrangement */
    	volatile XLogCtlData *xlogctl = XLogCtl;
    
    	SpinLockAcquire(&xlogctl->info_lck);
    	if (XLByteLT(xlogctl->asyncCommitLSN, asyncCommitLSN))
    		xlogctl->asyncCommitLSN = asyncCommitLSN;
    	SpinLockRelease(&xlogctl->info_lck);
    }
    
    /*
     * Advance minRecoveryPoint in control file.
     *
     * If we crash during recovery, we must reach this point again before the
     * database is consistent.
     *
     * If 'force' is true, 'lsn' argument is ignored. Otherwise, minRecoveryPoint
     * is only updated if it's not already greater than or equal to 'lsn'.
     */
    static void
    UpdateMinRecoveryPoint(XLogRecPtr lsn, bool force)
    {
    	/* Quick check using our local copy of the variable */
    	if (!updateMinRecoveryPoint || (!force && XLByteLE(lsn, minRecoveryPoint)))
    		return;
    
    	LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
    
    	/* update local copy */
    	minRecoveryPoint = ControlFile->minRecoveryPoint;
    
    	/*
    	 * An invalid minRecoveryPoint means that we need to recover all the WAL,
    	 * i.e., we're doing crash recovery.  We never modify the control file's
    	 * value in that case, so we can short-circuit future checks here too.
    	 */
    	if (minRecoveryPoint.xlogid == 0 && minRecoveryPoint.xrecoff == 0)
    		updateMinRecoveryPoint = false;
    	else if (force || XLByteLT(minRecoveryPoint, lsn))
    	{
    		/* use volatile pointer to prevent code rearrangement */
    		volatile XLogCtlData *xlogctl = XLogCtl;
    		XLogRecPtr	newMinRecoveryPoint;
    
    		/*
    		 * To avoid having to update the control file too often, we update it
    		 * all the way to the last record being replayed, even though 'lsn'
    		 * would suffice for correctness.  This also allows the 'force' case
    		 * to not need a valid 'lsn' value.
    		 *
    		 * Another important reason for doing it this way is that the passed
    		 * 'lsn' value could be bogus, i.e., past the end of available WAL, if
    		 * the caller got it from a corrupted heap page.  Accepting such a
    		 * value as the min recovery point would prevent us from coming up at
    		 * all.  Instead, we just log a warning and continue with recovery.
    		 * (See also the comments about corrupt LSNs in XLogFlush.)
    		 */
    		SpinLockAcquire(&xlogctl->info_lck);
    		newMinRecoveryPoint = xlogctl->replayEndRecPtr;
    		SpinLockRelease(&xlogctl->info_lck);
    
    		if (!force && XLByteLT(newMinRecoveryPoint, lsn))
    			elog(WARNING,
    			   "xlog min recovery request %X/%X is past current point %X/%X",
    				 lsn.xlogid, lsn.xrecoff,
    				 newMinRecoveryPoint.xlogid, newMinRecoveryPoint.xrecoff);
    
    		/* update control file */
    		if (XLByteLT(ControlFile->minRecoveryPoint, newMinRecoveryPoint))
    		{
    			ControlFile->minRecoveryPoint = newMinRecoveryPoint;
    			UpdateControlFile();
    			minRecoveryPoint = newMinRecoveryPoint;
    
    			ereport(DEBUG2,
    					(errmsg("updated min recovery point to %X/%X",
    						minRecoveryPoint.xlogid, minRecoveryPoint.xrecoff)));
    		}
    	}
    	LWLockRelease(ControlFileLock);
    }
    
    /*
     * Ensure that all XLOG data through the given position is flushed to disk.
     *
     * NOTE: this differs from XLogWrite mainly in that the WALWriteLock is not
     * already held, and we try to avoid acquiring it if possible.
     */
    void
    XLogFlush(XLogRecPtr record)
    {
    	XLogRecPtr	WriteRqstPtr;
    	XLogwrtRqst WriteRqst;
    
    	/*
    	 * During REDO, we are reading not writing WAL.  Therefore, instead of
    	 * trying to flush the WAL, we should update minRecoveryPoint instead. We
    	 * test XLogInsertAllowed(), not InRecovery, because we need the bgwriter
    	 * to act this way too, and because when the bgwriter tries to write the
    	 * end-of-recovery checkpoint, it should indeed flush.
    	 */
    	if (!XLogInsertAllowed())
    	{
    		UpdateMinRecoveryPoint(record, false);
    		return;
    	}
    
    	/* Quick exit if already known flushed */
    	if (XLByteLE(record, LogwrtResult.Flush))
    		return;
    
    #ifdef WAL_DEBUG
    	if (XLOG_DEBUG)
    		elog(LOG, "xlog flush request %X/%X; write %X/%X; flush %X/%X",
    			 record.xlogid, record.xrecoff,
    			 LogwrtResult.Write.xlogid, LogwrtResult.Write.xrecoff,
    			 LogwrtResult.Flush.xlogid, LogwrtResult.Flush.xrecoff);
    #endif
    
    	START_CRIT_SECTION();
    
    	/*
    	 * Since fsync is usually a horribly expensive operation, we try to
    	 * piggyback as much data as we can on each fsync: if we see any more data
    	 * entered into the xlog buffer, we'll write and fsync that too, so that
    	 * the final value of LogwrtResult.Flush is as large as possible. This
    	 * gives us some chance of avoiding another fsync immediately after.
    	 */
    
    	/* initialize to given target; may increase below */
    	WriteRqstPtr = record;
    
    	/* read LogwrtResult and update local state */
    	{
    		/* use volatile pointer to prevent code rearrangement */
    		volatile XLogCtlData *xlogctl = XLogCtl;
    
    		SpinLockAcquire(&xlogctl->info_lck);
    		if (XLByteLT(WriteRqstPtr, xlogctl->LogwrtRqst.Write))
    			WriteRqstPtr = xlogctl->LogwrtRqst.Write;
    		LogwrtResult = xlogctl->LogwrtResult;
    		SpinLockRelease(&xlogctl->info_lck);
    	}
    
    	/* done already? */
    	if (!XLByteLE(record, LogwrtResult.Flush))
    	{
    		/* now wait for the write lock */
    		LWLockAcquire(WALWriteLock, LW_EXCLUSIVE);
    		LogwrtResult = XLogCtl->Write.LogwrtResult;
    		if (!XLByteLE(record, LogwrtResult.Flush))
    		{
    			/* try to write/flush later additions to XLOG as well */
    			if (LWLockConditionalAcquire(WALInsertLock, LW_EXCLUSIVE))
    			{
    				XLogCtlInsert *Insert = &XLogCtl->Insert;
    				uint32		freespace = INSERT_FREESPACE(Insert);
    
    				if (freespace < SizeOfXLogRecord)		/* buffer is full */
    					WriteRqstPtr = XLogCtl->xlblocks[Insert->curridx];
    				else
    				{
    					WriteRqstPtr = XLogCtl->xlblocks[Insert->curridx];
    					WriteRqstPtr.xrecoff -= freespace;
    				}
    				LWLockRelease(WALInsertLock);
    				WriteRqst.Write = WriteRqstPtr;
    				WriteRqst.Flush = WriteRqstPtr;
    			}
    			else
    			{
    				WriteRqst.Write = WriteRqstPtr;
    				WriteRqst.Flush = record;
    			}
    			XLogWrite(WriteRqst, false, false);
    		}
    		LWLockRelease(WALWriteLock);
    	}
    
    	END_CRIT_SECTION();
    
    	/*
    	 * If we still haven't flushed to the request point then we have a
    	 * problem; most likely, the requested flush point is past end of XLOG.
    	 * This has been seen to occur when a disk page has a corrupted LSN.
    	 *
    	 * Formerly we treated this as a PANIC condition, but that hurts the
    	 * system's robustness rather than helping it: we do not want to take down
    	 * the whole system due to corruption on one data page.  In particular, if
    	 * the bad page is encountered again during recovery then we would be
    	 * unable to restart the database at all!  (This scenario actually
    	 * happened in the field several times with 7.1 releases.)	As of 8.4, bad
    	 * LSNs encountered during recovery are UpdateMinRecoveryPoint's problem;
    	 * the only time we can reach here during recovery is while flushing the
    	 * end-of-recovery checkpoint record, and we don't expect that to have a
    	 * bad LSN.
    	 *
    	 * Note that for calls from xact.c, the ERROR will be promoted to PANIC
    	 * since xact.c calls this routine inside a critical section.  However,
    	 * calls from bufmgr.c are not within critical sections and so we will not
    	 * force a restart for a bad LSN on a data page.
    	 */
    	if (XLByteLT(LogwrtResult.Flush, record))
    		elog(ERROR,
    		"xlog flush request %X/%X is not satisfied --- flushed only to %X/%X",
    			 record.xlogid, record.xrecoff,
    			 LogwrtResult.Flush.xlogid, LogwrtResult.Flush.xrecoff);
    }
    
    /*
     * Flush xlog, but without specifying exactly where to flush to.
     *
     * We normally flush only completed blocks; but if there is nothing to do on
     * that basis, we check for unflushed async commits in the current incomplete
     * block, and flush through the latest one of those.  Thus, if async commits
     * are not being used, we will flush complete blocks only.	We can guarantee
     * that async commits reach disk after at most three cycles; normally only
     * one or two.	(We allow XLogWrite to write "flexibly", meaning it can stop
     * at the end of the buffer ring; this makes a difference only with very high
     * load or long wal_writer_delay, but imposes one extra cycle for the worst
     * case for async commits.)
     *
     * This routine is invoked periodically by the background walwriter process.
     */
    void
    XLogBackgroundFlush(void)
    {
    	XLogRecPtr	WriteRqstPtr;
    	bool		flexible = true;
    
    	/* XLOG doesn't need flushing during recovery */
    	if (RecoveryInProgress())
    		return;
    
    	/* read LogwrtResult and update local state */
    	{
    		/* use volatile pointer to prevent code rearrangement */
    		volatile XLogCtlData *xlogctl = XLogCtl;
    
    		SpinLockAcquire(&xlogctl->info_lck);
    		LogwrtResult = xlogctl->LogwrtResult;
    		WriteRqstPtr = xlogctl->LogwrtRqst.Write;
    		SpinLockRelease(&xlogctl->info_lck);
    	}
    
    	/* back off to last completed page boundary */
    	WriteRqstPtr.xrecoff -= WriteRqstPtr.xrecoff % XLOG_BLCKSZ;
    
    	/* if we have already flushed that far, consider async commit records */
    	if (XLByteLE(WriteRqstPtr, LogwrtResult.Flush))
    	{
    		/* use volatile pointer to prevent code rearrangement */
    		volatile XLogCtlData *xlogctl = XLogCtl;
    
    		SpinLockAcquire(&xlogctl->info_lck);
    		WriteRqstPtr = xlogctl->asyncCommitLSN;
    		SpinLockRelease(&xlogctl->info_lck);
    		flexible = false;		/* ensure it all gets written */
    	}
    
    	/* Done if already known flushed */
    	if (XLByteLE(WriteRqstPtr, LogwrtResult.Flush))
    		return;
    
    #ifdef WAL_DEBUG
    	if (XLOG_DEBUG)
    		elog(LOG, "xlog bg flush request %X/%X; write %X/%X; flush %X/%X",
    			 WriteRqstPtr.xlogid, WriteRqstPtr.xrecoff,
    			 LogwrtResult.Write.xlogid, LogwrtResult.Write.xrecoff,
    			 LogwrtResult.Flush.xlogid, LogwrtResult.Flush.xrecoff);
    #endif
    
    	START_CRIT_SECTION();
    
    	/* now wait for the write lock */
    	LWLockAcquire(WALWriteLock, LW_EXCLUSIVE);
    	LogwrtResult = XLogCtl->Write.LogwrtResult;
    	if (!XLByteLE(WriteRqstPtr, LogwrtResult.Flush))
    	{
    		XLogwrtRqst WriteRqst;
    
    		WriteRqst.Write = WriteRqstPtr;
    		WriteRqst.Flush = WriteRqstPtr;
    		XLogWrite(WriteRqst, flexible, false);
    	}
    	LWLockRelease(WALWriteLock);
    
    	END_CRIT_SECTION();
    }
    
    /*
     * Test whether XLOG data has been flushed up to (at least) the given position.
     *
     * Returns true if a flush is still needed.  (It may be that someone else
     * is already in process of flushing that far, however.)
     */
    bool
    XLogNeedsFlush(XLogRecPtr record)
    {
    	/*
    	 * During recovery, we don't flush WAL but update minRecoveryPoint
    	 * instead. So "needs flush" is taken to mean whether minRecoveryPoint
    	 * would need to be updated.
    	 */
    	if (RecoveryInProgress())
    	{
    		/* Quick exit if already known updated */
    		if (XLByteLE(record, minRecoveryPoint) || !updateMinRecoveryPoint)
    			return false;
    
    		/*
    		 * Update local copy of minRecoveryPoint. But if the lock is busy,
    		 * just return a conservative guess.
    		 */
    		if (!LWLockConditionalAcquire(ControlFileLock, LW_SHARED))
    			return true;
    		minRecoveryPoint = ControlFile->minRecoveryPoint;
    		LWLockRelease(ControlFileLock);
    
    		/*
    		 * An invalid minRecoveryPoint means that we need to recover all the
    		 * WAL, i.e., we're doing crash recovery.  We never modify the control
    		 * file's value in that case, so we can short-circuit future checks
    		 * here too.
    		 */
    		if (minRecoveryPoint.xlogid == 0 && minRecoveryPoint.xrecoff == 0)
    			updateMinRecoveryPoint = false;
    
    		/* check again */
    		if (XLByteLE(record, minRecoveryPoint) || !updateMinRecoveryPoint)
    			return false;
    		else
    			return true;
    	}
    
    	/* Quick exit if already known flushed */
    	if (XLByteLE(record, LogwrtResult.Flush))
    		return false;
    
    	/* read LogwrtResult and update local state */
    	{
    		/* use volatile pointer to prevent code rearrangement */
    		volatile XLogCtlData *xlogctl = XLogCtl;
    
    		SpinLockAcquire(&xlogctl->info_lck);
    		LogwrtResult = xlogctl->LogwrtResult;
    		SpinLockRelease(&xlogctl->info_lck);
    	}
    
    	/* check again */
    	if (XLByteLE(record, LogwrtResult.Flush))
    		return false;
    
    	return true;
    }
    
    /*
     * Create a new XLOG file segment, or open a pre-existing one.
     *
     * log, seg: identify segment to be created/opened.
     *
     * *use_existent: if TRUE, OK to use a pre-existing file (else, any
     * pre-existing file will be deleted).	On return, TRUE if a pre-existing
     * file was used.
     *
     * use_lock: if TRUE, acquire ControlFileLock while moving file into
     * place.  This should be TRUE except during bootstrap log creation.  The
     * caller must *not* hold the lock at call.
     *
     * Returns FD of opened file.
     *
     * Note: errors here are ERROR not PANIC because we might or might not be
     * inside a critical section (eg, during checkpoint there is no reason to
     * take down the system on failure).  They will promote to PANIC if we are
     * in a critical section.
     */
    int
    XLogFileInit(uint32 log, uint32 seg,
    			 bool *use_existent, bool use_lock)
    {
    	char		path[MAXPGPATH];
    	char		tmppath[MAXPGPATH];
    	char	   *zbuffer;
    	uint32		installed_log;
    	uint32		installed_seg;
    	int			max_advance;
    	int			fd;
    	int			nbytes;
    
    	XLogFilePath(path, ThisTimeLineID, log, seg);
    
    	/*
    	 * Try to use existent file (checkpoint maker may have created it already)
    	 */
    	if (*use_existent)
    	{
    		fd = BasicOpenFile(path, O_RDWR | PG_BINARY | get_sync_bit(sync_method),
    						   S_IRUSR | S_IWUSR);
    		if (fd < 0)
    		{
    			if (errno != ENOENT)
    				ereport(ERROR,
    						(errcode_for_file_access(),
    						 errmsg("could not open file \"%s\" (log file %u, segment %u): %m",
    								path, log, seg)));
    		}
    		else
    			return fd;
    	}
    
    	/*
    	 * Initialize an empty (all zeroes) segment.  NOTE: it is possible that
    	 * another process is doing the same thing.  If so, we will end up
    	 * pre-creating an extra log segment.  That seems OK, and better than
    	 * holding the lock throughout this lengthy process.
    	 */
    	elog(DEBUG2, "creating and filling new WAL file");
    
    	snprintf(tmppath, MAXPGPATH, XLOGDIR "/xlogtemp.%d", (int) getpid());
    
    	unlink(tmppath);
    
    	/* do not use get_sync_bit() here --- want to fsync only at end of fill */
    	fd = BasicOpenFile(tmppath, O_RDWR | O_CREAT | O_EXCL | PG_BINARY,
    					   S_IRUSR | S_IWUSR);
    	if (fd < 0)
    		ereport(ERROR,
    				(errcode_for_file_access(),
    				 errmsg("could not create file \"%s\": %m", tmppath)));
    
    	/*
    	 * Zero-fill the file.	We have to do this the hard way to ensure that all
    	 * the file space has really been allocated --- on platforms that allow
    	 * "holes" in files, just seeking to the end doesn't allocate intermediate
    	 * space.  This way, we know that we have all the space and (after the
    	 * fsync below) that all the indirect blocks are down on disk.	Therefore,
    	 * fdatasync(2) or O_DSYNC will be sufficient to sync future writes to the
    	 * log file.
    	 *
    	 * Note: palloc zbuffer, instead of just using a local char array, to
    	 * ensure it is reasonably well-aligned; this may save a few cycles
    	 * transferring data to the kernel.
    	 */
    	zbuffer = (char *) palloc0(XLOG_BLCKSZ);
    	for (nbytes = 0; nbytes < XLogSegSize; nbytes += XLOG_BLCKSZ)
    	{
    		errno = 0;
    		if ((int) write(fd, zbuffer, XLOG_BLCKSZ) != (int) XLOG_BLCKSZ)
    		{
    			int			save_errno = errno;
    
    			/*
    			 * If we fail to make the file, delete it to release disk space
    			 */
    			unlink(tmppath);
    			/* if write didn't set errno, assume problem is no disk space */
    			errno = save_errno ? save_errno : ENOSPC;
    
    			ereport(ERROR,
    					(errcode_for_file_access(),
    					 errmsg("could not write to file \"%s\": %m", tmppath)));
    		}
    	}
    	pfree(zbuffer);
    
    	if (pg_fsync(fd) != 0)
    		ereport(ERROR,
    				(errcode_for_file_access(),
    				 errmsg("could not fsync file \"%s\": %m", tmppath)));
    
    	if (close(fd))
    		ereport(ERROR,
    				(errcode_for_file_access(),
    				 errmsg("could not close file \"%s\": %m", tmppath)));
    
    	/*
    	 * Now move the segment into place with its final name.
    	 *
    	 * If caller didn't want to use a pre-existing file, get rid of any
    	 * pre-existing file.  Otherwise, cope with possibility that someone else
    	 * has created the file while we were filling ours: if so, use ours to
    	 * pre-create a future log segment.
    	 */
    	installed_log = log;
    	installed_seg = seg;
    	max_advance = XLOGfileslop;
    	if (!InstallXLogFileSegment(&installed_log, &installed_seg, tmppath,
    								*use_existent, &max_advance,
    								use_lock))
    	{
    		/*
    		 * No need for any more future segments, or InstallXLogFileSegment()
    		 * failed to rename the file into place. If the rename failed, opening
    		 * the file below will fail.
    		 */
    		unlink(tmppath);
    	}
    
    	/* Set flag to tell caller there was no existent file */
    	*use_existent = false;
    
    	/* Now open original target segment (might not be file I just made) */
    	fd = BasicOpenFile(path, O_RDWR | PG_BINARY | get_sync_bit(sync_method),
    					   S_IRUSR | S_IWUSR);
    	if (fd < 0)
    		ereport(ERROR,
    				(errcode_for_file_access(),
    		   errmsg("could not open file \"%s\" (log file %u, segment %u): %m",
    				  path, log, seg)));
    
    	elog(DEBUG2, "done creating and filling new WAL file");
    
    	return fd;
    }
    
    /*
     * Create a new XLOG file segment by copying a pre-existing one.
     *
     * log, seg: identify segment to be created.
     *
     * srcTLI, srclog, srcseg: identify segment to be copied (could be from
     *		a different timeline)
     *
     * Currently this is only used during recovery, and so there are no locking
     * considerations.	But we should be just as tense as XLogFileInit to avoid
     * emplacing a bogus file.
     */
    static void
    XLogFileCopy(uint32 log, uint32 seg,
    			 TimeLineID srcTLI, uint32 srclog, uint32 srcseg)
    {
    	char		path[MAXPGPATH];
    	char		tmppath[MAXPGPATH];
    	char		buffer[XLOG_BLCKSZ];
    	int			srcfd;
    	int			fd;
    	int			nbytes;
    
    	/*
    	 * Open the source file
    	 */
    	XLogFilePath(path, srcTLI, srclog, srcseg);
    	srcfd = BasicOpenFile(path, O_RDONLY | PG_BINARY, 0);
    	if (srcfd < 0)
    		ereport(ERROR,
    				(errcode_for_file_access(),
    				 errmsg("could not open file \"%s\": %m", path)));
    
    	/*
    	 * Copy into a temp file name.
    	 */
    	snprintf(tmppath, MAXPGPATH, XLOGDIR "/xlogtemp.%d", (int) getpid());
    
    	unlink(tmppath);
    
    	/* do not use get_sync_bit() here --- want to fsync only at end of fill */
    	fd = BasicOpenFile(tmppath, O_RDWR | O_CREAT | O_EXCL | PG_BINARY,
    					   S_IRUSR | S_IWUSR);
    	if (fd < 0)
    		ereport(ERROR,
    				(errcode_for_file_access(),
    				 errmsg("could not create file \"%s\": %m", tmppath)));
    
    	/*
    	 * Do the data copying.
    	 */
    	for (nbytes = 0; nbytes < XLogSegSize; nbytes += sizeof(buffer))
    	{
    		errno = 0;
    		if ((int) read(srcfd, buffer, sizeof(buffer)) != (int) sizeof(buffer))
    		{
    			if (errno != 0)
    				ereport(ERROR,
    						(errcode_for_file_access(),
    						 errmsg("could not read file \"%s\": %m", path)));
    			else
    				ereport(ERROR,
    						(errmsg("not enough data in file \"%s\"", path)));
    		}
    		errno = 0;
    		if ((int) write(fd, buffer, sizeof(buffer)) != (int) sizeof(buffer))
    		{
    			int			save_errno = errno;
    
    			/*
    			 * If we fail to make the file, delete it to release disk space
    			 */
    			unlink(tmppath);
    			/* if write didn't set errno, assume problem is no disk space */
    			errno = save_errno ? save_errno : ENOSPC;
    
    			ereport(ERROR,
    					(errcode_for_file_access(),
    					 errmsg("could not write to file \"%s\": %m", tmppath)));
    		}
    	}
    
    	if (pg_fsync(fd) != 0)
    		ereport(ERROR,
    				(errcode_for_file_access(),
    				 errmsg("could not fsync file \"%s\": %m", tmppath)));
    
    	if (close(fd))
    		ereport(ERROR,
    				(errcode_for_file_access(),
    				 errmsg("could not close file \"%s\": %m", tmppath)));
    
    	close(srcfd);
    
    	/*
    	 * Now move the segment into place with its final name.
    	 */
    	if (!InstallXLogFileSegment(&log, &seg, tmppath, false, NULL, false))
    		elog(ERROR, "InstallXLogFileSegment should not have failed");
    }
    
    /*
     * Install a new XLOG segment file as a current or future log segment.
     *
     * This is used both to install a newly-created segment (which has a temp
     * filename while it's being created) and to recycle an old segment.
     *
     * *log, *seg: identify segment to install as (or first possible target).
     * When find_free is TRUE, these are modified on return to indicate the
     * actual installation location or last segment searched.
     *
     * tmppath: initial name of file to install.  It will be renamed into place.
     *
     * find_free: if TRUE, install the new segment at the first empty log/seg
     * number at or after the passed numbers.  If FALSE, install the new segment
     * exactly where specified, deleting any existing segment file there.
     *
     * *max_advance: maximum number of log/seg slots to advance past the starting
     * point.  Fail if no free slot is found in this range.  On return, reduced
     * by the number of slots skipped over.  (Irrelevant, and may be NULL,
     * when find_free is FALSE.)
     *
     * use_lock: if TRUE, acquire ControlFileLock while moving file into
     * place.  This should be TRUE except during bootstrap log creation.  The
     * caller must *not* hold the lock at call.
     *
     * Returns TRUE if the file was installed successfully.  FALSE indicates that
     * max_advance limit was exceeded, or an error occurred while renaming the
     * file into place.
     */
    static bool
    InstallXLogFileSegment(uint32 *log, uint32 *seg, char *tmppath,
    					   bool find_free, int *max_advance,
    					   bool use_lock)
    {
    	char		path[MAXPGPATH];
    	struct stat stat_buf;
    
    	XLogFilePath(path, ThisTimeLineID, *log, *seg);
    
    	/*
    	 * We want to be sure that only one process does this at a time.
    	 */
    	if (use_lock)
    		LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
    
    	if (!find_free)
    	{
    		/* Force installation: get rid of any pre-existing segment file */
    		unlink(path);
    	}
    	else
    	{
    		/* Find a free slot to put it in */
    		while (stat(path, &stat_buf) == 0)
    		{
    			if (*max_advance <= 0)
    			{
    				/* Failed to find a free slot within specified range */
    				if (use_lock)
    					LWLockRelease(ControlFileLock);
    				return false;
    			}
    			NextLogSeg(*log, *seg);
    			(*max_advance)--;
    			XLogFilePath(path, ThisTimeLineID, *log, *seg);
    		}
    	}
    
    	/*
    	 * Prefer link() to rename() here just to be really sure that we don't
    	 * overwrite an existing logfile.  However, there shouldn't be one, so
    	 * rename() is an acceptable substitute except for the truly paranoid.
    	 */
    #if HAVE_WORKING_LINK
    	if (link(tmppath, path) < 0)
    	{
    		if (use_lock)
    			LWLockRelease(ControlFileLock);
    		ereport(LOG,
    				(errcode_for_file_access(),
    				 errmsg("could not link file \"%s\" to \"%s\" (initialization of log file %u, segment %u): %m",
    						tmppath, path, *log, *seg)));
    		return false;
    	}
    	unlink(tmppath);
    #else
    	if (rename(tmppath, path) < 0)
    	{
    		if (use_lock)
    			LWLockRelease(ControlFileLock);
    		ereport(LOG,
    				(errcode_for_file_access(),
    				 errmsg("could not rename file \"%s\" to \"%s\" (initialization of log file %u, segment %u): %m",
    						tmppath, path, *log, *seg)));
    		return false;
    	}
    #endif
    
    	if (use_lock)
    		LWLockRelease(ControlFileLock);
    
    	return true;
    }
    
    /*
     * Open a pre-existing logfile segment for writing.
     */
    int
    XLogFileOpen(uint32 log, uint32 seg)
    {
    	char		path[MAXPGPATH];
    	int			fd;
    
    	XLogFilePath(path, ThisTimeLineID, log, seg);
    
    	fd = BasicOpenFile(path, O_RDWR | PG_BINARY | get_sync_bit(sync_method),
    					   S_IRUSR | S_IWUSR);
    	if (fd < 0)
    		ereport(PANIC,
    				(errcode_for_file_access(),
    		   errmsg("could not open file \"%s\" (log file %u, segment %u): %m",
    				  path, log, seg)));
    
    	return fd;
    }
    
    /*
     * Open a logfile segment for reading (during recovery).
     *
     * If fromArchive is true, the segment is retrieved from archive, otherwise
     * it's read from pg_xlog.
     */
    static int
    XLogFileRead(uint32 log, uint32 seg, int emode, TimeLineID tli,
    			 bool fromArchive, bool notfoundOk)
    {
    	char		xlogfname[MAXFNAMELEN];
    	char		activitymsg[MAXFNAMELEN + 16];
    	char		path[MAXPGPATH];
    	int			fd;
    
    	XLogFileName(xlogfname, tli, log, seg);
    
    	if (fromArchive)
    	{
    		/* Report recovery progress in PS display */
    		snprintf(activitymsg, sizeof(activitymsg), "waiting for %s",
    				 xlogfname);
    		set_ps_display(activitymsg, false);
    
    		restoredFromArchive = RestoreArchivedFile(path, xlogfname,
    												  "RECOVERYXLOG",
    												  XLogSegSize);
    		if (!restoredFromArchive)
    			return -1;
    	}
    	else
    	{
    		XLogFilePath(path, tli, log, seg);
    		restoredFromArchive = false;
    	}
    
    	fd = BasicOpenFile(path, O_RDONLY | PG_BINARY, 0);
    	if (fd >= 0)
    	{
    		/* Success! */
    		curFileTLI = tli;
    
    		/* Report recovery progress in PS display */
    		snprintf(activitymsg, sizeof(activitymsg), "recovering %s",
    				 xlogfname);
    		set_ps_display(activitymsg, false);
    
    		return fd;
    	}
    	if (errno != ENOENT || !notfoundOk) /* unexpected failure? */
    		ereport(PANIC,
    				(errcode_for_file_access(),
    		   errmsg("could not open file \"%s\" (log file %u, segment %u): %m",
    				  path, log, seg)));
    	return -1;
    }
    
    /*
     * Open a logfile segment for reading (during recovery).
     *
     * This version searches for the segment with any TLI listed in expectedTLIs.
     * If not in StandbyMode and fromArchive is true, the segment is also
     * searched in pg_xlog if not found in archive.
     */
    static int
    XLogFileReadAnyTLI(uint32 log, uint32 seg, int emode, bool fromArchive)
    {
    	char		path[MAXPGPATH];
    	ListCell   *cell;
    	int			fd;
    
    	/*
    	 * Loop looking for a suitable timeline ID: we might need to read any of
    	 * the timelines listed in expectedTLIs.
    	 *
    	 * We expect curFileTLI on entry to be the TLI of the preceding file in
    	 * sequence, or 0 if there was no predecessor.	We do not allow curFileTLI
    	 * to go backwards; this prevents us from picking up the wrong file when a
    	 * parent timeline extends to higher segment numbers than the child we
    	 * want to read.
    	 */
    	foreach(cell, expectedTLIs)
    	{
    		TimeLineID	tli = (TimeLineID) lfirst_int(cell);
    
    		if (tli < curFileTLI)
    			break;				/* don't bother looking at too-old TLIs */
    
    		fd = XLogFileRead(log, seg, emode, tli, fromArchive, true);
    		if (fd != -1)
    			return fd;
    
    		/*
    		 * If not in StandbyMode, fall back to searching pg_xlog. In
    		 * StandbyMode we're streaming segments from the primary to pg_xlog,
    		 * and we mustn't confuse the (possibly partial) segments in pg_xlog
    		 * with complete segments ready to be applied. We rather wait for the
    		 * records to arrive through streaming.
    		 */
    		if (!StandbyMode && fromArchive)
    		{
    			fd = XLogFileRead(log, seg, emode, tli, false, true);
    			if (fd != -1)
    				return fd;
    		}
    	}
    
    	/* Couldn't find it.  For simplicity, complain about front timeline */
    	XLogFilePath(path, recoveryTargetTLI, log, seg);
    	errno = ENOENT;
    	ereport(emode,
    			(errcode_for_file_access(),
    		   errmsg("could not open file \"%s\" (log file %u, segment %u): %m",
    				  path, log, seg)));
    	return -1;
    }
    
    /*
     * Close the current logfile segment for writing.
     */
    static void
    XLogFileClose(void)
    {
    	Assert(openLogFile >= 0);
    
    	/*
    	 * WAL segment files will not be re-read in normal operation, so we advise
    	 * the OS to release any cached pages.	But do not do so if WAL archiving
    	 * or streaming is active, because archiver and walsender process could
    	 * use the cache to read the WAL segment.
    	 */
    #if defined(USE_POSIX_FADVISE) && defined(POSIX_FADV_DONTNEED)
    	if (!XLogIsNeeded())
    		(void) posix_fadvise(openLogFile, 0, 0, POSIX_FADV_DONTNEED);
    #endif
    
    	if (close(openLogFile))
    		ereport(PANIC,
    				(errcode_for_file_access(),
    				 errmsg("could not close log file %u, segment %u: %m",
    						openLogId, openLogSeg)));
    	openLogFile = -1;
    }
    
    /*
     * Attempt to retrieve the specified file from off-line archival storage.
     * If successful, fill "path" with its complete path (note that this will be
     * a temp file name that doesn't follow the normal naming convention), and
     * return TRUE.
     *
     * If not successful, fill "path" with the name of the normal on-line file
     * (which may or may not actually exist, but we'll try to use it), and return
     * FALSE.
     *
     * For fixed-size files, the caller may pass the expected size as an
     * additional crosscheck on successful recovery.  If the file size is not
     * known, set expectedSize = 0.
     */
    static bool
    RestoreArchivedFile(char *path, const char *xlogfname,
    					const char *recovername, off_t expectedSize)
    {
    	char		xlogpath[MAXPGPATH];
    	char		xlogRestoreCmd[MAXPGPATH];
    	char		lastRestartPointFname[MAXPGPATH];
    	char	   *dp;
    	char	   *endp;
    	const char *sp;
    	int			rc;
    	bool		signaled;
    	struct stat stat_buf;
    	uint32		restartLog;
    	uint32		restartSeg;
    
    	/* In standby mode, restore_command might not be supplied */
    	if (recoveryRestoreCommand == NULL)
    		goto not_available;
    
    	/*
    	 * When doing archive recovery, we always prefer an archived log file even
    	 * if a file of the same name exists in XLOGDIR.  The reason is that the
    	 * file in XLOGDIR could be an old, un-filled or partly-filled version
    	 * that was copied and restored as part of backing up $PGDATA.
    	 *
    	 * We could try to optimize this slightly by checking the local copy
    	 * lastchange timestamp against the archived copy, but we have no API to
    	 * do this, nor can we guarantee that the lastchange timestamp was
    	 * preserved correctly when we copied to archive. Our aim is robustness,
    	 * so we elect not to do this.
    	 *
    	 * If we cannot obtain the log file from the archive, however, we will try
    	 * to use the XLOGDIR file if it exists.  This is so that we can make use
    	 * of log segments that weren't yet transferred to the archive.
    	 *
    	 * Notice that we don't actually overwrite any files when we copy back
    	 * from archive because the recoveryRestoreCommand may inadvertently
    	 * restore inappropriate xlogs, or they may be corrupt, so we may wish to
    	 * fallback to the segments remaining in current XLOGDIR later. The
    	 * copy-from-archive filename is always the same, ensuring that we don't
    	 * run out of disk space on long recoveries.
    	 */
    	snprintf(xlogpath, MAXPGPATH, XLOGDIR "/%s", recovername);
    
    	/*
    	 * Make sure there is no existing file named recovername.
    	 */
    	if (stat(xlogpath, &stat_buf) != 0)
    	{
    		if (errno != ENOENT)
    			ereport(FATAL,
    					(errcode_for_file_access(),
    					 errmsg("could not stat file \"%s\": %m",
    							xlogpath)));
    	}
    	else
    	{
    		if (unlink(xlogpath) != 0)
    			ereport(FATAL,
    					(errcode_for_file_access(),
    					 errmsg("could not remove file \"%s\": %m",
    							xlogpath)));
    	}
    
    	/*
    	 * Calculate the archive file cutoff point for use during log shipping
    	 * replication. All files earlier than this point can be deleted from the
    	 * archive, though there is no requirement to do so.
    	 *
    	 * We initialise this with the filename of an InvalidXLogRecPtr, which
    	 * will prevent the deletion of any WAL files from the archive because of
    	 * the alphabetic sorting property of WAL filenames.
    	 *
    	 * Once we have successfully located the redo pointer of the checkpoint
    	 * from which we start recovery we never request a file prior to the redo
    	 * pointer of the last restartpoint. When redo begins we know that we have
    	 * successfully located it, so there is no need for additional status
    	 * flags to signify the point when we can begin deleting WAL files from
    	 * the archive.
    	 */
    	if (InRedo)
    	{
    		XLByteToSeg(ControlFile->checkPointCopy.redo,
    					restartLog, restartSeg);
    		XLogFileName(lastRestartPointFname,
    					 ControlFile->checkPointCopy.ThisTimeLineID,
    					 restartLog, restartSeg);
    		/* we shouldn't need anything earlier than last restart point */
    		Assert(strcmp(lastRestartPointFname, xlogfname) <= 0);
    	}
    	else
    		XLogFileName(lastRestartPointFname, 0, 0, 0);
    
    	/*
    	 * construct the command to be executed
    	 */
    	dp = xlogRestoreCmd;
    	endp = xlogRestoreCmd + MAXPGPATH - 1;
    	*endp = '\0';
    
    	for (sp = recoveryRestoreCommand; *sp; sp++)
    	{
    		if (*sp == '%')
    		{
    			switch (sp[1])
    			{
    				case 'p':
    					/* %p: relative path of target file */
    					sp++;
    					StrNCpy(dp, xlogpath, endp - dp);
    					make_native_path(dp);
    					dp += strlen(dp);
    					break;
    				case 'f':
    					/* %f: filename of desired file */
    					sp++;
    					StrNCpy(dp, xlogfname, endp - dp);
    					dp += strlen(dp);
    					break;
    				case 'r':
    					/* %r: filename of last restartpoint */
    					sp++;
    					StrNCpy(dp, lastRestartPointFname, endp - dp);
    					dp += strlen(dp);
    					break;
    				case '%':
    					/* convert %% to a single % */
    					sp++;
    					if (dp < endp)
    						*dp++ = *sp;
    					break;
    				default:
    					/* otherwise treat the % as not special */
    					if (dp < endp)
    						*dp++ = *sp;
    					break;
    			}
    		}
    		else
    		{
    			if (dp < endp)
    				*dp++ = *sp;
    		}
    	}
    	*dp = '\0';
    
    	ereport(DEBUG3,
    			(errmsg_internal("executing restore command \"%s\"",
    							 xlogRestoreCmd)));
    
    	/*
    	 * Set in_restore_command to tell the signal handler that we should exit
    	 * right away on SIGTERM. We know that we're at a safe point to do that.
    	 * Check if we had already received the signal, so that we don't miss a
    	 * shutdown request received just before this.
    	 */
    	in_restore_command = true;
    	if (shutdown_requested)
    		proc_exit(1);
    
    	/*
    	 * Copy xlog from archival storage to XLOGDIR
    	 */
    	rc = system(xlogRestoreCmd);
    
    	in_restore_command = false;
    
    	if (rc == 0)
    	{
    		/*
    		 * command apparently succeeded, but let's make sure the file is
    		 * really there now and has the correct size.
    		 */
    		if (stat(xlogpath, &stat_buf) == 0)
    		{
    			if (expectedSize > 0 && stat_buf.st_size != expectedSize)
    			{
    				int			elevel;
    
    				/*
    				 * If we find a partial file in standby mode, we assume it's
    				 * because it's just being copied to the archive, and keep
    				 * trying.
    				 *
    				 * Otherwise treat a wrong-sized file as FATAL to ensure the
    				 * DBA would notice it, but is that too strong? We could try
    				 * to plow ahead with a local copy of the file ... but the
    				 * problem is that there probably isn't one, and we'd
    				 * incorrectly conclude we've reached the end of WAL and we're
    				 * done recovering ...
    				 */
    				if (StandbyMode && stat_buf.st_size < expectedSize)
    					elevel = DEBUG1;
    				else
    					elevel = FATAL;
    				ereport(elevel,
    						(errmsg("archive file \"%s\" has wrong size: %lu instead of %lu",
    								xlogfname,
    								(unsigned long) stat_buf.st_size,
    								(unsigned long) expectedSize)));
    				return false;
    			}
    			else
    			{
    				ereport(LOG,
    						(errmsg("restored log file \"%s\" from archive",
    								xlogfname)));
    				strcpy(path, xlogpath);
    				return true;
    			}
    		}
    		else
    		{
    			/* stat failed */
    			if (errno != ENOENT)
    				ereport(FATAL,
    						(errcode_for_file_access(),
    						 errmsg("could not stat file \"%s\": %m",
    								xlogpath)));
    		}
    	}
    
    	/*
    	 * Remember, we rollforward UNTIL the restore fails so failure here is
    	 * just part of the process... that makes it difficult to determine
    	 * whether the restore failed because there isn't an archive to restore,
    	 * or because the administrator has specified the restore program
    	 * incorrectly.  We have to assume the former.
    	 *
    	 * However, if the failure was due to any sort of signal, it's best to
    	 * punt and abort recovery.  (If we "return false" here, upper levels will
    	 * assume that recovery is complete and start up the database!) It's
    	 * essential to abort on child SIGINT and SIGQUIT, because per spec
    	 * system() ignores SIGINT and SIGQUIT while waiting; if we see one of
    	 * those it's a good bet we should have gotten it too.
    	 *
    	 * On SIGTERM, assume we have received a fast shutdown request, and exit
    	 * cleanly. It's pure chance whether we receive the SIGTERM first, or the
    	 * child process. If we receive it first, the signal handler will call
    	 * proc_exit, otherwise we do it here. If we or the child process received
    	 * SIGTERM for any other reason than a fast shutdown request, postmaster
    	 * will perform an immediate shutdown when it sees us exiting
    	 * unexpectedly.
    	 *
    	 * Per the Single Unix Spec, shells report exit status > 128 when a called
    	 * command died on a signal.  Also, 126 and 127 are used to report
    	 * problems such as an unfindable command; treat those as fatal errors
    	 * too.
    	 */
    	if (WIFSIGNALED(rc) && WTERMSIG(rc) == SIGTERM)
    		proc_exit(1);
    
    	signaled = WIFSIGNALED(rc) || WEXITSTATUS(rc) > 125;
    
    	ereport(signaled ? FATAL : DEBUG2,
    		(errmsg("could not restore file \"%s\" from archive: return code %d",
    				xlogfname, rc)));
    
    not_available:
    
    	/*
    	 * if an archived file is not available, there might still be a version of
    	 * this file in XLOGDIR, so return that as the filename to open.
    	 *
    	 * In many recovery scenarios we expect this to fail also, but if so that
    	 * just means we've reached the end of WAL.
    	 */
    	snprintf(path, MAXPGPATH, XLOGDIR "/%s", xlogfname);
    	return false;
    }
    
    /*
     * Attempt to execute an external shell command during recovery.
     *
     * 'command' is the shell command to be executed, 'commandName' is a
     * human-readable name describing the command emitted in the logs. If
     * 'failonSignal' is true and the command is killed by a signal, a FATAL
     * error is thrown. Otherwise a WARNING is emitted.
     *
     * This is currently used for restore_end_command and restartpoint_command.
     */
    static void
    ExecuteRecoveryCommand(char *command, char *commandName, bool failOnSignal)
    {
    	char		xlogRecoveryCmd[MAXPGPATH];
    	char		lastRestartPointFname[MAXPGPATH];
    	char	   *dp;
    	char	   *endp;
    	const char *sp;
    	int			rc;
    	bool		signaled;
    	uint32		restartLog;
    	uint32		restartSeg;
    
    	Assert(command && commandName);
    
    	/*
    	 * Calculate the archive file cutoff point for use during log shipping
    	 * replication. All files earlier than this point can be deleted from the
    	 * archive, though there is no requirement to do so.
    	 */
    	LWLockAcquire(ControlFileLock, LW_SHARED);
    	XLByteToSeg(ControlFile->checkPointCopy.redo,
    				restartLog, restartSeg);
    	XLogFileName(lastRestartPointFname,
    				 ControlFile->checkPointCopy.ThisTimeLineID,
    				 restartLog, restartSeg);
    	LWLockRelease(ControlFileLock);
    
    	/*
    	 * construct the command to be executed
    	 */
    	dp = xlogRecoveryCmd;
    	endp = xlogRecoveryCmd + MAXPGPATH - 1;
    	*endp = '\0';
    
    	for (sp = command; *sp; sp++)
    	{
    		if (*sp == '%')
    		{
    			switch (sp[1])
    			{
    				case 'r':
    					/* %r: filename of last restartpoint */
    					sp++;
    					StrNCpy(dp, lastRestartPointFname, endp - dp);
    					dp += strlen(dp);
    					break;
    				case '%':
    					/* convert %% to a single % */
    					sp++;
    					if (dp < endp)
    						*dp++ = *sp;
    					break;
    				default:
    					/* otherwise treat the % as not special */
    					if (dp < endp)
    						*dp++ = *sp;
    					break;
    			}
    		}
    		else
    		{
    			if (dp < endp)
    				*dp++ = *sp;
    		}
    	}
    	*dp = '\0';
    
    	ereport(DEBUG3,
    			(errmsg_internal("executing %s \"%s\"", commandName, command)));
    
    	/*
    	 * execute the constructed command
    	 */
    	rc = system(xlogRecoveryCmd);
    	if (rc != 0)
    	{
    		/*
    		 * If the failure was due to any sort of signal, it's best to punt and
    		 * abort recovery. See also detailed comments on signals in
    		 * RestoreArchivedFile().
    		 */
    		signaled = WIFSIGNALED(rc) || WEXITSTATUS(rc) > 125;
    
    		/*
    		 * translator: First %s represents a recovery.conf parameter name like
    		 * "recovery_end_command", and the 2nd is the value of that parameter.
    		 */
    		ereport((signaled && failOnSignal) ? FATAL : WARNING,
    				(errmsg("%s \"%s\": return code %d", commandName,
    						command, rc)));
    	}
    }
    
    /*
     * Preallocate log files beyond the specified log endpoint.
     *
     * XXX this is currently extremely conservative, since it forces only one
     * future log segment to exist, and even that only if we are 75% done with
     * the current one.  This is only appropriate for very low-WAL-volume systems.
     * High-volume systems will be OK once they've built up a sufficient set of
     * recycled log segments, but the startup transient is likely to include
     * a lot of segment creations by foreground processes, which is not so good.
     */
    static void
    PreallocXlogFiles(XLogRecPtr endptr)
    {
    	uint32		_logId;
    	uint32		_logSeg;
    	int			lf;
    	bool		use_existent;
    
    	XLByteToPrevSeg(endptr, _logId, _logSeg);
    	if ((endptr.xrecoff - 1) % XLogSegSize >=
    		(uint32) (0.75 * XLogSegSize))
    	{
    		NextLogSeg(_logId, _logSeg);
    		use_existent = true;
    		lf = XLogFileInit(_logId, _logSeg, &use_existent, true);
    		close(lf);
    		if (!use_existent)
    			CheckpointStats.ckpt_segs_added++;
    	}
    }
    
    /*
     * Recycle or remove all log files older or equal to passed log/seg#
     *
     * endptr is current (or recent) end of xlog; this is used to determine
     * whether we want to recycle rather than delete no-longer-wanted log files.
     */
    static void
    RemoveOldXlogFiles(uint32 log, uint32 seg, XLogRecPtr endptr)
    {
    	uint32		endlogId;
    	uint32		endlogSeg;
    	int			max_advance;
    	DIR		   *xldir;
    	struct dirent *xlde;
    	char		lastoff[MAXFNAMELEN];
    	char		path[MAXPGPATH];
    
    #ifdef WIN32
    	char		newpath[MAXPGPATH];
    #endif
    	struct stat statbuf;
    
    	/*
    	 * Initialize info about where to try to recycle to.  We allow recycling
    	 * segments up to XLOGfileslop segments beyond the current XLOG location.
    	 */
    	XLByteToPrevSeg(endptr, endlogId, endlogSeg);
    	max_advance = XLOGfileslop;
    
    	xldir = AllocateDir(XLOGDIR);
    	if (xldir == NULL)
    		ereport(ERROR,
    				(errcode_for_file_access(),
    				 errmsg("could not open transaction log directory \"%s\": %m",
    						XLOGDIR)));
    
    	XLogFileName(lastoff, ThisTimeLineID, log, seg);
    
    	while ((xlde = ReadDir(xldir, XLOGDIR)) != NULL)
    	{
    		/*
    		 * We ignore the timeline part of the XLOG segment identifiers in
    		 * deciding whether a segment is still needed.	This ensures that we
    		 * won't prematurely remove a segment from a parent timeline. We could
    		 * probably be a little more proactive about removing segments of
    		 * non-parent timelines, but that would be a whole lot more
    		 * complicated.
    		 *
    		 * We use the alphanumeric sorting property of the filenames to decide
    		 * which ones are earlier than the lastoff segment.
    		 */
    		if (strlen(xlde->d_name) == 24 &&
    			strspn(xlde->d_name, "0123456789ABCDEF") == 24 &&
    			strcmp(xlde->d_name + 8, lastoff + 8) <= 0)
    		{
    			/*
    			 * Normally we don't delete old XLOG files during recovery to
    			 * avoid accidentally deleting a file that looks stale due to a
    			 * bug or hardware issue, but in fact contains important data.
    			 * During streaming recovery, however, we will eventually fill the
    			 * disk if we never clean up, so we have to. That's not an issue
    			 * with file-based archive recovery because in that case we
    			 * restore one XLOG file at a time, on-demand, and with a
    			 * different filename that can't be confused with regular XLOG
    			 * files.
    			 */
    			if (WalRcvInProgress() || XLogArchiveCheckDone(xlde->d_name))
    			{
    				snprintf(path, MAXPGPATH, XLOGDIR "/%s", xlde->d_name);
    
    				/*
    				 * Before deleting the file, see if it can be recycled as a
    				 * future log segment. Only recycle normal files, pg_standby
    				 * for example can create symbolic links pointing to a
    				 * separate archive directory.
    				 */
    				if (lstat(path, &statbuf) == 0 && S_ISREG(statbuf.st_mode) &&
    					InstallXLogFileSegment(&endlogId, &endlogSeg, path,
    										   true, &max_advance, true))
    				{
    					ereport(DEBUG2,
    							(errmsg("recycled transaction log file \"%s\"",
    									xlde->d_name)));
    					CheckpointStats.ckpt_segs_recycled++;
    					/* Needn't recheck that slot on future iterations */
    					if (max_advance > 0)
    					{
    						NextLogSeg(endlogId, endlogSeg);
    						max_advance--;
    					}
    				}
    				else
    				{
    					/* No need for any more future segments... */
    					int			rc;
    
    					ereport(DEBUG2,
    							(errmsg("removing transaction log file \"%s\"",
    									xlde->d_name)));
    
    #ifdef WIN32
    
    					/*
    					 * On Windows, if another process (e.g another backend)
    					 * holds the file open in FILE_SHARE_DELETE mode, unlink
    					 * will succeed, but the file will still show up in
    					 * directory listing until the last handle is closed. To
    					 * avoid confusing the lingering deleted file for a live
    					 * WAL file that needs to be archived, rename it before
    					 * deleting it.
    					 *
    					 * If another process holds the file open without
    					 * FILE_SHARE_DELETE flag, rename will fail. We'll try
    					 * again at the next checkpoint.
    					 */
    					snprintf(newpath, MAXPGPATH, "%s.deleted", path);
    					if (rename(path, newpath) != 0)
    					{
    						ereport(LOG,
    								(errcode_for_file_access(),
    								 errmsg("could not rename old transaction log file \"%s\": %m",
    										path)));
    						continue;
    					}
    					rc = unlink(newpath);
    #else
    					rc = unlink(path);
    #endif
    					if (rc != 0)
    					{
    						ereport(LOG,
    								(errcode_for_file_access(),
    								 errmsg("could not remove old transaction log file \"%s\": %m",
    										path)));
    						continue;
    					}
    					CheckpointStats.ckpt_segs_removed++;
    				}
    
    				XLogArchiveCleanup(xlde->d_name);
    			}
    		}
    	}
    
    	FreeDir(xldir);
    }
    
    /*
     * Verify whether pg_xlog and pg_xlog/archive_status exist.
     * If the latter does not exist, recreate it.
     *
     * It is not the goal of this function to verify the contents of these
     * directories, but to help in cases where someone has performed a cluster
     * copy for PITR purposes but omitted pg_xlog from the copy.
     *
     * We could also recreate pg_xlog if it doesn't exist, but a deliberate
     * policy decision was made not to.  It is fairly common for pg_xlog to be
     * a symlink, and if that was the DBA's intent then automatically making a
     * plain directory would result in degraded performance with no notice.
     */
    static void
    ValidateXLOGDirectoryStructure(void)
    {
    	char		path[MAXPGPATH];
    	struct stat stat_buf;
    
    	/* Check for pg_xlog; if it doesn't exist, error out */
    	if (stat(XLOGDIR, &stat_buf) != 0 ||
    		!S_ISDIR(stat_buf.st_mode))
    		ereport(FATAL,
    				(errmsg("required WAL directory \"%s\" does not exist",
    						XLOGDIR)));
    
    	/* Check for archive_status */
    	snprintf(path, MAXPGPATH, XLOGDIR "/archive_status");
    	if (stat(path, &stat_buf) == 0)
    	{
    		/* Check for weird cases where it exists but isn't a directory */
    		if (!S_ISDIR(stat_buf.st_mode))
    			ereport(FATAL,
    					(errmsg("required WAL directory \"%s\" does not exist",
    							path)));
    	}
    	else
    	{
    		ereport(LOG,
    				(errmsg("creating missing WAL directory \"%s\"", path)));
    		if (mkdir(path, 0700) < 0)
    			ereport(FATAL,
    					(errmsg("could not create missing directory \"%s\": %m",
    							path)));
    	}
    }
    
    /*
     * Remove previous backup history files.  This also retries creation of
     * .ready files for any backup history files for which XLogArchiveNotify
     * failed earlier.
     */
    static void
    CleanupBackupHistory(void)
    {
    	DIR		   *xldir;
    	struct dirent *xlde;
    	char		path[MAXPGPATH];
    
    	xldir = AllocateDir(XLOGDIR);
    	if (xldir == NULL)
    		ereport(ERROR,
    				(errcode_for_file_access(),
    				 errmsg("could not open transaction log directory \"%s\": %m",
    						XLOGDIR)));
    
    	while ((xlde = ReadDir(xldir, XLOGDIR)) != NULL)
    	{
    		if (strlen(xlde->d_name) > 24 &&
    			strspn(xlde->d_name, "0123456789ABCDEF") == 24 &&
    			strcmp(xlde->d_name + strlen(xlde->d_name) - strlen(".backup"),
    				   ".backup") == 0)
    		{
    			if (XLogArchiveCheckDone(xlde->d_name))
    			{
    				ereport(DEBUG2,
    				(errmsg("removing transaction log backup history file \"%s\"",
    						xlde->d_name)));
    				snprintf(path, MAXPGPATH, XLOGDIR "/%s", xlde->d_name);
    				unlink(path);
    				XLogArchiveCleanup(xlde->d_name);
    			}
    		}
    	}
    
    	FreeDir(xldir);
    }
    
    /*
     * Restore the backup blocks present in an XLOG record, if any.
     *
     * We assume all of the record has been read into memory at *record.
     *
     * Note: when a backup block is available in XLOG, we restore it
     * unconditionally, even if the page in the database appears newer.
     * This is to protect ourselves against database pages that were partially
     * or incorrectly written during a crash.  We assume that the XLOG data
     * must be good because it has passed a CRC check, while the database
     * page might not be.  This will force us to replay all subsequent
     * modifications of the page that appear in XLOG, rather than possibly
     * ignoring them as already applied, but that's not a huge drawback.
     *
     * If 'cleanup' is true, a cleanup lock is used when restoring blocks.
     * Otherwise, a normal exclusive lock is used.	During crash recovery, that's
     * just pro forma because there can't be any regular backends in the system,
     * but in hot standby mode the distinction is important. The 'cleanup'
     * argument applies to all backup blocks in the WAL record, that suffices for
     * now.
     */
    void
    RestoreBkpBlocks(XLogRecPtr lsn, XLogRecord *record, bool cleanup)
    {
    	Buffer		buffer;
    	Page		page;
    	BkpBlock	bkpb;
    	char	   *blk;
    	int			i;
    
    	if (!(record->xl_info & XLR_BKP_BLOCK_MASK))
    		return;
    
    	blk = (char *) XLogRecGetData(record) + record->xl_len;
    	for (i = 0; i < XLR_MAX_BKP_BLOCKS; i++)
    	{
    		if (!(record->xl_info & XLR_SET_BKP_BLOCK(i)))
    			continue;
    
    		memcpy(&bkpb, blk, sizeof(BkpBlock));
    		blk += sizeof(BkpBlock);
    
    		buffer = XLogReadBufferExtended(bkpb.node, bkpb.fork, bkpb.block,
    										RBM_ZERO);
    		Assert(BufferIsValid(buffer));
    		if (cleanup)
    			LockBufferForCleanup(buffer);
    		else
    			LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
    
    		page = (Page) BufferGetPage(buffer);
    
    		if (bkpb.hole_length == 0)
    		{
    			memcpy((char *) page, blk, BLCKSZ);
    		}
    		else
    		{
    			/* must zero-fill the hole */
    			MemSet((char *) page, 0, BLCKSZ);
    			memcpy((char *) page, blk, bkpb.hole_offset);
    			memcpy((char *) page + (bkpb.hole_offset + bkpb.hole_length),
    				   blk + bkpb.hole_offset,
    				   BLCKSZ - (bkpb.hole_offset + bkpb.hole_length));
    		}
    
    		PageSetLSN(page, lsn);
    		PageSetTLI(page, ThisTimeLineID);
    		MarkBufferDirty(buffer);
    		UnlockReleaseBuffer(buffer);
    
    		blk += BLCKSZ - bkpb.hole_length;
    	}
    }
    
    /*
     * CRC-check an XLOG record.  We do not believe the contents of an XLOG
     * record (other than to the minimal extent of computing the amount of
     * data to read in) until we've checked the CRCs.
     *
     * We assume all of the record has been read into memory at *record.
     */
    static bool
    RecordIsValid(XLogRecord *record, XLogRecPtr recptr, int emode)
    {
    	pg_crc32	crc;
    	int			i;
    	uint32		len = record->xl_len;
    	BkpBlock	bkpb;
    	char	   *blk;
    
    	/* First the rmgr data */
    	INIT_CRC32(crc);
    	COMP_CRC32(crc, XLogRecGetData(record), len);
    
    	/* Add in the backup blocks, if any */
    	blk = (char *) XLogRecGetData(record) + len;
    	for (i = 0; i < XLR_MAX_BKP_BLOCKS; i++)
    	{
    		uint32		blen;
    
    		if (!(record->xl_info & XLR_SET_BKP_BLOCK(i)))
    			continue;
    
    		memcpy(&bkpb, blk, sizeof(BkpBlock));
    		if (bkpb.hole_offset + bkpb.hole_length > BLCKSZ)
    		{
    			ereport(emode,
    					(errmsg("incorrect hole size in record at %X/%X",
    							recptr.xlogid, recptr.xrecoff)));
    			return false;
    		}
    		blen = sizeof(BkpBlock) + BLCKSZ - bkpb.hole_length;
    		COMP_CRC32(crc, blk, blen);
    		blk += blen;
    	}
    
    	/* Check that xl_tot_len agrees with our calculation */
    	if (blk != (char *) record + record->xl_tot_len)
    	{
    		ereport(emode,
    				(errmsg("incorrect total length in record at %X/%X",
    						recptr.xlogid, recptr.xrecoff)));
    		return false;
    	}
    
    	/* Finally include the record header */
    	COMP_CRC32(crc, (char *) record + sizeof(pg_crc32),
    			   SizeOfXLogRecord - sizeof(pg_crc32));
    	FIN_CRC32(crc);
    
    	if (!EQ_CRC32(record->xl_crc, crc))
    	{
    		ereport(emode,
    		(errmsg("incorrect resource manager data checksum in record at %X/%X",
    				recptr.xlogid, recptr.xrecoff)));
    		return false;
    	}
    
    	return true;
    }
    
    /*
     * Attempt to read an XLOG record.
     *
     * If RecPtr is not NULL, try to read a record at that position.  Otherwise
     * try to read a record just after the last one previously read.
     *
     * If no valid record is available, returns NULL, or fails if emode is PANIC.
     * (emode must be either PANIC, LOG)
     *
     * The record is copied into readRecordBuf, so that on successful return,
     * the returned record pointer always points there.
     */
    static XLogRecord *
    ReadRecord(XLogRecPtr *RecPtr, int emode_arg, bool fetching_ckpt)
    {
    	XLogRecord *record;
    	char	   *buffer;
    	XLogRecPtr	tmpRecPtr = EndRecPtr;
    	bool		randAccess = false;
    	uint32		len,
    				total_len;
    	uint32		targetRecOff;
    	uint32		pageHeaderSize;
    	int			emode;
    
    	/*
    	 * We don't expect any invalid records during streaming recovery: we
    	 * should never hit the end of WAL because we wait for it to be streamed.
    	 * Therefore treat any broken WAL as PANIC, instead of failing over.
    	 */
    	if (StandbyMode)
    		emode = PANIC;
    	else
    		emode = emode_arg;
    
    	if (readBuf == NULL)
    	{
    		/*
    		 * First time through, permanently allocate readBuf.  We do it this
    		 * way, rather than just making a static array, for two reasons: (1)
    		 * no need to waste the storage in most instantiations of the backend;
    		 * (2) a static char array isn't guaranteed to have any particular
    		 * alignment, whereas malloc() will provide MAXALIGN'd storage.
    		 */
    		readBuf = (char *) malloc(XLOG_BLCKSZ);
    		Assert(readBuf != NULL);
    	}
    
    	if (RecPtr == NULL)
    	{
    		RecPtr = &tmpRecPtr;
    
    		/*
    		 * Align recptr to next page if no more records can fit on the current
    		 * page.
    		 */
    		if (XLOG_BLCKSZ - (RecPtr->xrecoff % XLOG_BLCKSZ) < SizeOfXLogRecord)
    		{
    			NextLogPage(tmpRecPtr);
    			/* We will account for page header size below */
    		}
    
    		if (tmpRecPtr.xrecoff >= XLogFileSize)
    		{
    			(tmpRecPtr.xlogid)++;
    			tmpRecPtr.xrecoff = 0;
    		}
    	}
    	else
    	{
    		if (!XRecOffIsValid(RecPtr->xrecoff))
    			ereport(PANIC,
    					(errmsg("invalid record offset at %X/%X",
    							RecPtr->xlogid, RecPtr->xrecoff)));
    
    		/*
    		 * Since we are going to a random position in WAL, forget any prior
    		 * state about what timeline we were in, and allow it to be any
    		 * timeline in expectedTLIs.  We also set a flag to allow curFileTLI
    		 * to go backwards (but we can't reset that variable right here, since
    		 * we might not change files at all).
    		 */
    		lastPageTLI = 0;		/* see comment in ValidXLOGHeader */
    		randAccess = true;		/* allow curFileTLI to go backwards too */
    	}
    
    	/* Read the page containing the record */
    	if (!XLogPageRead(RecPtr, emode, fetching_ckpt, randAccess))
    		return NULL;
    
    	pageHeaderSize = XLogPageHeaderSize((XLogPageHeader) readBuf);
    	targetRecOff = RecPtr->xrecoff % XLOG_BLCKSZ;
    	if (targetRecOff == 0)
    	{
    		/*
    		 * Can only get here in the continuing-from-prev-page case, because
    		 * XRecOffIsValid eliminated the zero-page-offset case otherwise. Need
    		 * to skip over the new page's header.
    		 */
    		tmpRecPtr.xrecoff += pageHeaderSize;
    		targetRecOff = pageHeaderSize;
    	}
    	else if (targetRecOff < pageHeaderSize)
    	{
    		ereport(emode,
    				(errmsg("invalid record offset at %X/%X",
    						RecPtr->xlogid, RecPtr->xrecoff)));
    		goto next_record_is_invalid;
    	}
    	if ((((XLogPageHeader) readBuf)->xlp_info & XLP_FIRST_IS_CONTRECORD) &&
    		targetRecOff == pageHeaderSize)
    	{
    		ereport(emode,
    				(errmsg("contrecord is requested by %X/%X",
    						RecPtr->xlogid, RecPtr->xrecoff)));
    		goto next_record_is_invalid;
    	}
    	record = (XLogRecord *) ((char *) readBuf + RecPtr->xrecoff % XLOG_BLCKSZ);
    
    	/*
    	 * xl_len == 0 is bad data for everything except XLOG SWITCH, where it is
    	 * required.
    	 */
    	if (record->xl_rmid == RM_XLOG_ID && record->xl_info == XLOG_SWITCH)
    	{
    		if (record->xl_len != 0)
    		{
    			ereport(emode,
    					(errmsg("invalid xlog switch record at %X/%X",
    							RecPtr->xlogid, RecPtr->xrecoff)));
    			goto next_record_is_invalid;
    		}
    	}
    	else if (record->xl_len == 0)
    	{
    		ereport(emode,
    				(errmsg("record with zero length at %X/%X",
    						RecPtr->xlogid, RecPtr->xrecoff)));
    		goto next_record_is_invalid;
    	}
    	if (record->xl_tot_len < SizeOfXLogRecord + record->xl_len ||
    		record->xl_tot_len > SizeOfXLogRecord + record->xl_len +
    		XLR_MAX_BKP_BLOCKS * (sizeof(BkpBlock) + BLCKSZ))
    	{
    		ereport(emode,
    				(errmsg("invalid record length at %X/%X",
    						RecPtr->xlogid, RecPtr->xrecoff)));
    		goto next_record_is_invalid;
    	}
    	if (record->xl_rmid > RM_MAX_ID)
    	{
    		ereport(emode,
    				(errmsg("invalid resource manager ID %u at %X/%X",
    						record->xl_rmid, RecPtr->xlogid, RecPtr->xrecoff)));
    		goto next_record_is_invalid;
    	}
    	if (randAccess)
    	{
    		/*
    		 * We can't exactly verify the prev-link, but surely it should be less
    		 * than the record's own address.
    		 */
    		if (!XLByteLT(record->xl_prev, *RecPtr))
    		{
    			ereport(emode,
    					(errmsg("record with incorrect prev-link %X/%X at %X/%X",
    							record->xl_prev.xlogid, record->xl_prev.xrecoff,
    							RecPtr->xlogid, RecPtr->xrecoff)));
    			goto next_record_is_invalid;
    		}
    	}
    	else
    	{
    		/*
    		 * Record's prev-link should exactly match our previous location. This
    		 * check guards against torn WAL pages where a stale but valid-looking
    		 * WAL record starts on a sector boundary.
    		 */
    		if (!XLByteEQ(record->xl_prev, ReadRecPtr))
    		{
    			ereport(emode,
    					(errmsg("record with incorrect prev-link %X/%X at %X/%X",
    							record->xl_prev.xlogid, record->xl_prev.xrecoff,
    							RecPtr->xlogid, RecPtr->xrecoff)));
    			goto next_record_is_invalid;
    		}
    	}
    
    	/*
    	 * Allocate or enlarge readRecordBuf as needed.  To avoid useless small
    	 * increases, round its size to a multiple of XLOG_BLCKSZ, and make sure
    	 * it's at least 4*Max(BLCKSZ, XLOG_BLCKSZ) to start with.  (That is
    	 * enough for all "normal" records, but very large commit or abort records
    	 * might need more space.)
    	 */
    	total_len = record->xl_tot_len;
    	if (total_len > readRecordBufSize)
    	{
    		uint32		newSize = total_len;
    
    		newSize += XLOG_BLCKSZ - (newSize % XLOG_BLCKSZ);
    		newSize = Max(newSize, 4 * Max(BLCKSZ, XLOG_BLCKSZ));
    		if (readRecordBuf)
    			free(readRecordBuf);
    		readRecordBuf = (char *) malloc(newSize);
    		if (!readRecordBuf)
    		{
    			readRecordBufSize = 0;
    			/* We treat this as a "bogus data" condition */
    			ereport(emode,
    					(errmsg("record length %u at %X/%X too long",
    							total_len, RecPtr->xlogid, RecPtr->xrecoff)));
    			goto next_record_is_invalid;
    		}
    		readRecordBufSize = newSize;
    	}
    
    	buffer = readRecordBuf;
    	len = XLOG_BLCKSZ - RecPtr->xrecoff % XLOG_BLCKSZ;
    	if (total_len > len)
    	{
    		/* Need to reassemble record */
    		XLogContRecord *contrecord;
    		XLogRecPtr	pagelsn;
    		uint32		gotlen = len;
    
    		/* Initialize pagelsn to the beginning of the page this record is on */
    		pagelsn = *RecPtr;
    		pagelsn.xrecoff = (pagelsn.xrecoff / XLOG_BLCKSZ) * XLOG_BLCKSZ;
    
    		memcpy(buffer, record, len);
    		record = (XLogRecord *) buffer;
    		buffer += len;
    		for (;;)
    		{
    			/* Calculate pointer to beginning of next page */
    			pagelsn.xrecoff += XLOG_BLCKSZ;
    			if (pagelsn.xrecoff >= XLogFileSize)
    			{
    				(pagelsn.xlogid)++;
    				pagelsn.xrecoff = 0;
    			}
    			/* Wait for the next page to become available */
    			if (!XLogPageRead(&pagelsn, emode, false, false))
    				return NULL;
    
    			/* Check that the continuation record looks valid */
    			if (!(((XLogPageHeader) readBuf)->xlp_info & XLP_FIRST_IS_CONTRECORD))
    			{
    				ereport(emode,
    						(errmsg("there is no contrecord flag in log file %u, segment %u, offset %u",
    								readId, readSeg, readOff)));
    				goto next_record_is_invalid;
    			}
    			pageHeaderSize = XLogPageHeaderSize((XLogPageHeader) readBuf);
    			contrecord = (XLogContRecord *) ((char *) readBuf + pageHeaderSize);
    			if (contrecord->xl_rem_len == 0 ||
    				total_len != (contrecord->xl_rem_len + gotlen))
    			{
    				ereport(emode,
    						(errmsg("invalid contrecord length %u in log file %u, segment %u, offset %u",
    								contrecord->xl_rem_len,
    								readId, readSeg, readOff)));
    				goto next_record_is_invalid;
    			}
    			len = XLOG_BLCKSZ - pageHeaderSize - SizeOfXLogContRecord;
    			if (contrecord->xl_rem_len > len)
    			{
    				memcpy(buffer, (char *) contrecord + SizeOfXLogContRecord, len);
    				gotlen += len;
    				buffer += len;
    				continue;
    			}
    			memcpy(buffer, (char *) contrecord + SizeOfXLogContRecord,
    				   contrecord->xl_rem_len);
    			break;
    		}
    		if (!RecordIsValid(record, *RecPtr, emode))
    			goto next_record_is_invalid;
    		pageHeaderSize = XLogPageHeaderSize((XLogPageHeader) readBuf);
    		EndRecPtr.xlogid = readId;
    		EndRecPtr.xrecoff = readSeg * XLogSegSize + readOff +
    			pageHeaderSize +
    			MAXALIGN(SizeOfXLogContRecord + contrecord->xl_rem_len);
    
    		ReadRecPtr = *RecPtr;
    		/* needn't worry about XLOG SWITCH, it can't cross page boundaries */
    		return record;
    	}
    
    	/* Record does not cross a page boundary */
    	if (!RecordIsValid(record, *RecPtr, emode))
    		goto next_record_is_invalid;
    	EndRecPtr.xlogid = RecPtr->xlogid;
    	EndRecPtr.xrecoff = RecPtr->xrecoff + MAXALIGN(total_len);
    
    	ReadRecPtr = *RecPtr;
    	memcpy(buffer, record, total_len);
    
    	/*
    	 * Special processing if it's an XLOG SWITCH record
    	 */
    	if (record->xl_rmid == RM_XLOG_ID && record->xl_info == XLOG_SWITCH)
    	{
    		/* Pretend it extends to end of segment */
    		EndRecPtr.xrecoff += XLogSegSize - 1;
    		EndRecPtr.xrecoff -= EndRecPtr.xrecoff % XLogSegSize;
    
    		/*
    		 * Pretend that readBuf contains the last page of the segment. This is
    		 * just to avoid Assert failure in StartupXLOG if XLOG ends with this
    		 * segment.
    		 */
    		readOff = XLogSegSize - XLOG_BLCKSZ;
    	}
    	return (XLogRecord *) buffer;
    
    next_record_is_invalid:;
    	if (readFile >= 0)
    	{
    		close(readFile);
    		readFile = -1;
    	}
    	return NULL;
    }
    
    /*
     * Check whether the xlog header of a page just read in looks valid.
     *
     * This is just a convenience subroutine to avoid duplicated code in
     * ReadRecord.	It's not intended for use from anywhere else.
     */
    static bool
    ValidXLOGHeader(XLogPageHeader hdr, int emode)
    {
    	XLogRecPtr	recaddr;
    
    	if (hdr->xlp_magic != XLOG_PAGE_MAGIC)
    	{
    		ereport(emode,
    				(errmsg("invalid magic number %04X in log file %u, segment %u, offset %u",
    						hdr->xlp_magic, readId, readSeg, readOff)));
    		return false;
    	}
    	if ((hdr->xlp_info & ~XLP_ALL_FLAGS) != 0)
    	{
    		ereport(emode,
    				(errmsg("invalid info bits %04X in log file %u, segment %u, offset %u",
    						hdr->xlp_info, readId, readSeg, readOff)));
    		return false;
    	}
    	if (hdr->xlp_info & XLP_LONG_HEADER)
    	{
    		XLogLongPageHeader longhdr = (XLogLongPageHeader) hdr;
    
    		if (longhdr->xlp_sysid != ControlFile->system_identifier)
    		{
    			char		fhdrident_str[32];
    			char		sysident_str[32];
    
    			/*
    			 * Format sysids separately to keep platform-dependent format code
    			 * out of the translatable message string.
    			 */
    			snprintf(fhdrident_str, sizeof(fhdrident_str), UINT64_FORMAT,
    					 longhdr->xlp_sysid);
    			snprintf(sysident_str, sizeof(sysident_str), UINT64_FORMAT,
    					 ControlFile->system_identifier);
    			ereport(emode,
    					(errmsg("WAL file is from different system"),
    					 errdetail("WAL file SYSID is %s, pg_control SYSID is %s",
    							   fhdrident_str, sysident_str)));
    			return false;
    		}
    		if (longhdr->xlp_seg_size != XLogSegSize)
    		{
    			ereport(emode,
    					(errmsg("WAL file is from different system"),
    					 errdetail("Incorrect XLOG_SEG_SIZE in page header.")));
    			return false;
    		}
    		if (longhdr->xlp_xlog_blcksz != XLOG_BLCKSZ)
    		{
    			ereport(emode,
    					(errmsg("WAL file is from different system"),
    					 errdetail("Incorrect XLOG_BLCKSZ in page header.")));
    			return false;
    		}
    	}
    	else if (readOff == 0)
    	{
    		/* hmm, first page of file doesn't have a long header? */
    		ereport(emode,
    				(errmsg("invalid info bits %04X in log file %u, segment %u, offset %u",
    						hdr->xlp_info, readId, readSeg, readOff)));
    		return false;
    	}
    
    	recaddr.xlogid = readId;
    	recaddr.xrecoff = readSeg * XLogSegSize + readOff;
    	if (!XLByteEQ(hdr->xlp_pageaddr, recaddr))
    	{
    		ereport(emode,
    				(errmsg("unexpected pageaddr %X/%X in log file %u, segment %u, offset %u",
    						hdr->xlp_pageaddr.xlogid, hdr->xlp_pageaddr.xrecoff,
    						readId, readSeg, readOff)));
    		return false;
    	}
    
    	/*
    	 * Check page TLI is one of the expected values.
    	 */
    	if (!list_member_int(expectedTLIs, (int) hdr->xlp_tli))
    	{
    		ereport(emode,
    				(errmsg("unexpected timeline ID %u in log file %u, segment %u, offset %u",
    						hdr->xlp_tli,
    						readId, readSeg, readOff)));
    		return false;
    	}
    
    	/*
    	 * Since child timelines are always assigned a TLI greater than their
    	 * immediate parent's TLI, we should never see TLI go backwards across
    	 * successive pages of a consistent WAL sequence.
    	 *
    	 * Of course this check should only be applied when advancing sequentially
    	 * across pages; therefore ReadRecord resets lastPageTLI to zero when
    	 * going to a random page.
    	 */
    	if (hdr->xlp_tli < lastPageTLI)
    	{
    		ereport(emode,
    				(errmsg("out-of-sequence timeline ID %u (after %u) in log file %u, segment %u, offset %u",
    						hdr->xlp_tli, lastPageTLI,
    						readId, readSeg, readOff)));
    		return false;
    	}
    	lastPageTLI = hdr->xlp_tli;
    	return true;
    }
    
    /*
     * Try to read a timeline's history file.
     *
     * If successful, return the list of component TLIs (the given TLI followed by
     * its ancestor TLIs).	If we can't find the history file, assume that the
     * timeline has no parents, and return a list of just the specified timeline
     * ID.
     */
    static List *
    readTimeLineHistory(TimeLineID targetTLI)
    {
    	List	   *result;
    	char		path[MAXPGPATH];
    	char		histfname[MAXFNAMELEN];
    	char		fline[MAXPGPATH];
    	FILE	   *fd;
    
    	/* Timeline 1 does not have a history file, so no need to check */
    	if (targetTLI == 1)
    		return list_make1_int((int) targetTLI);
    
    	if (InArchiveRecovery)
    	{
    		TLHistoryFileName(histfname, targetTLI);
    		RestoreArchivedFile(path, histfname, "RECOVERYHISTORY", 0);
    	}
    	else
    		TLHistoryFilePath(path, targetTLI);
    
    	fd = AllocateFile(path, "r");
    	if (fd == NULL)
    	{
    		if (errno != ENOENT)
    			ereport(FATAL,
    					(errcode_for_file_access(),
    					 errmsg("could not open file \"%s\": %m", path)));
    		/* Not there, so assume no parents */
    		return list_make1_int((int) targetTLI);
    	}
    
    	result = NIL;
    
    	/*
    	 * Parse the file...
    	 */
    	while (fgets(fline, sizeof(fline), fd) != NULL)
    	{
    		/* skip leading whitespace and check for # comment */
    		char	   *ptr;
    		char	   *endptr;
    		TimeLineID	tli;
    
    		for (ptr = fline; *ptr; ptr++)
    		{
    			if (!isspace((unsigned char) *ptr))
    				break;
    		}
    		if (*ptr == '\0' || *ptr == '#')
    			continue;
    
    		/* expect a numeric timeline ID as first field of line */
    		tli = (TimeLineID) strtoul(ptr, &endptr, 0);
    		if (endptr == ptr)
    			ereport(FATAL,
    					(errmsg("syntax error in history file: %s", fline),
    					 errhint("Expected a numeric timeline ID.")));
    
    		if (result &&
    			tli <= (TimeLineID) linitial_int(result))
    			ereport(FATAL,
    					(errmsg("invalid data in history file: %s", fline),
    				   errhint("Timeline IDs must be in increasing sequence.")));
    
    		/* Build list with newest item first */
    		result = lcons_int((int) tli, result);
    
    		/* we ignore the remainder of each line */
    	}
    
    	FreeFile(fd);
    
    	if (result &&
    		targetTLI <= (TimeLineID) linitial_int(result))
    		ereport(FATAL,
    				(errmsg("invalid data in history file \"%s\"", path),
    			errhint("Timeline IDs must be less than child timeline's ID.")));
    
    	result = lcons_int((int) targetTLI, result);
    
    	ereport(DEBUG3,
    			(errmsg_internal("history of timeline %u is %s",
    							 targetTLI, nodeToString(result))));
    
    	return result;
    }
    
    /*
     * Probe whether a timeline history file exists for the given timeline ID
     */
    static bool
    existsTimeLineHistory(TimeLineID probeTLI)
    {
    	char		path[MAXPGPATH];
    	char		histfname[MAXFNAMELEN];
    	FILE	   *fd;
    
    	/* Timeline 1 does not have a history file, so no need to check */
    	if (probeTLI == 1)
    		return false;
    
    	if (InArchiveRecovery)
    	{
    		TLHistoryFileName(histfname, probeTLI);
    		RestoreArchivedFile(path, histfname, "RECOVERYHISTORY", 0);
    	}
    	else
    		TLHistoryFilePath(path, probeTLI);
    
    	fd = AllocateFile(path, "r");
    	if (fd != NULL)
    	{
    		FreeFile(fd);
    		return true;
    	}
    	else
    	{
    		if (errno != ENOENT)
    			ereport(FATAL,
    					(errcode_for_file_access(),
    					 errmsg("could not open file \"%s\": %m", path)));
    		return false;
    	}
    }
    
    /*
     * Find the newest existing timeline, assuming that startTLI exists.
     *
     * Note: while this is somewhat heuristic, it does positively guarantee
     * that (result + 1) is not a known timeline, and therefore it should
     * be safe to assign that ID to a new timeline.
     */
    static TimeLineID
    findNewestTimeLine(TimeLineID startTLI)
    {
    	TimeLineID	newestTLI;
    	TimeLineID	probeTLI;
    
    	/*
    	 * The algorithm is just to probe for the existence of timeline history
    	 * files.  XXX is it useful to allow gaps in the sequence?
    	 */
    	newestTLI = startTLI;
    
    	for (probeTLI = startTLI + 1;; probeTLI++)
    	{
    		if (existsTimeLineHistory(probeTLI))
    		{
    			newestTLI = probeTLI;		/* probeTLI exists */
    		}
    		else
    		{
    			/* doesn't exist, assume we're done */
    			break;
    		}
    	}
    
    	return newestTLI;
    }
    
    /*
     * Create a new timeline history file.
     *
     *	newTLI: ID of the new timeline
     *	parentTLI: ID of its immediate parent
     *	endTLI et al: ID of the last used WAL file, for annotation purposes
     *
     * Currently this is only used during recovery, and so there are no locking
     * considerations.	But we should be just as tense as XLogFileInit to avoid
     * emplacing a bogus file.
     */
    static void
    writeTimeLineHistory(TimeLineID newTLI, TimeLineID parentTLI,
    					 TimeLineID endTLI, uint32 endLogId, uint32 endLogSeg)
    {
    	char		path[MAXPGPATH];
    	char		tmppath[MAXPGPATH];
    	char		histfname[MAXFNAMELEN];
    	char		xlogfname[MAXFNAMELEN];
    	char		buffer[BLCKSZ];
    	int			srcfd;
    	int			fd;
    	int			nbytes;
    
    	Assert(newTLI > parentTLI); /* else bad selection of newTLI */
    
    	/*
    	 * Write into a temp file name.
    	 */
    	snprintf(tmppath, MAXPGPATH, XLOGDIR "/xlogtemp.%d", (int) getpid());
    
    	unlink(tmppath);
    
    	/* do not use get_sync_bit() here --- want to fsync only at end of fill */
    	fd = BasicOpenFile(tmppath, O_RDWR | O_CREAT | O_EXCL,
    					   S_IRUSR | S_IWUSR);
    	if (fd < 0)
    		ereport(ERROR,
    				(errcode_for_file_access(),
    				 errmsg("could not create file \"%s\": %m", tmppath)));
    
    	/*
    	 * If a history file exists for the parent, copy it verbatim
    	 */
    	if (InArchiveRecovery)
    	{
    		TLHistoryFileName(histfname, parentTLI);
    		RestoreArchivedFile(path, histfname, "RECOVERYHISTORY", 0);
    	}
    	else
    		TLHistoryFilePath(path, parentTLI);
    
    	srcfd = BasicOpenFile(path, O_RDONLY, 0);
    	if (srcfd < 0)
    	{
    		if (errno != ENOENT)
    			ereport(ERROR,
    					(errcode_for_file_access(),
    					 errmsg("could not open file \"%s\": %m", path)));
    		/* Not there, so assume parent has no parents */
    	}
    	else
    	{
    		for (;;)
    		{
    			errno = 0;
    			nbytes = (int) read(srcfd, buffer, sizeof(buffer));
    			if (nbytes < 0 || errno != 0)
    				ereport(ERROR,
    						(errcode_for_file_access(),
    						 errmsg("could not read file \"%s\": %m", path)));
    			if (nbytes == 0)
    				break;
    			errno = 0;
    			if ((int) write(fd, buffer, nbytes) != nbytes)
    			{
    				int			save_errno = errno;
    
    				/*
    				 * If we fail to make the file, delete it to release disk
    				 * space
    				 */
    				unlink(tmppath);
    
    				/*
    				 * if write didn't set errno, assume problem is no disk space
    				 */
    				errno = save_errno ? save_errno : ENOSPC;
    
    				ereport(ERROR,
    						(errcode_for_file_access(),
    					 errmsg("could not write to file \"%s\": %m", tmppath)));
    			}
    		}
    		close(srcfd);
    	}
    
    	/*
    	 * Append one line with the details of this timeline split.
    	 *
    	 * If we did have a parent file, insert an extra newline just in case the
    	 * parent file failed to end with one.
    	 */
    	XLogFileName(xlogfname, endTLI, endLogId, endLogSeg);
    
    	snprintf(buffer, sizeof(buffer),
    			 "%s%u\t%s\t%s transaction %u at %s\n",
    			 (srcfd < 0) ? "" : "\n",
    			 parentTLI,
    			 xlogfname,
    			 recoveryStopAfter ? "after" : "before",
    			 recoveryStopXid,
    			 timestamptz_to_str(recoveryStopTime));
    
    	nbytes = strlen(buffer);
    	errno = 0;
    	if ((int) write(fd, buffer, nbytes) != nbytes)
    	{
    		int			save_errno = errno;
    
    		/*
    		 * If we fail to make the file, delete it to release disk space
    		 */
    		unlink(tmppath);
    		/* if write didn't set errno, assume problem is no disk space */
    		errno = save_errno ? save_errno : ENOSPC;
    
    		ereport(ERROR,
    				(errcode_for_file_access(),
    				 errmsg("could not write to file \"%s\": %m", tmppath)));
    	}
    
    	if (pg_fsync(fd) != 0)
    		ereport(ERROR,
    				(errcode_for_file_access(),
    				 errmsg("could not fsync file \"%s\": %m", tmppath)));
    
    	if (close(fd))
    		ereport(ERROR,
    				(errcode_for_file_access(),
    				 errmsg("could not close file \"%s\": %m", tmppath)));
    
    
    	/*
    	 * Now move the completed history file into place with its final name.
    	 */
    	TLHistoryFilePath(path, newTLI);
    
    	/*
    	 * Prefer link() to rename() here just to be really sure that we don't
    	 * overwrite an existing logfile.  However, there shouldn't be one, so
    	 * rename() is an acceptable substitute except for the truly paranoid.
    	 */
    #if HAVE_WORKING_LINK
    	if (link(tmppath, path) < 0)
    		ereport(ERROR,
    				(errcode_for_file_access(),
    				 errmsg("could not link file \"%s\" to \"%s\": %m",
    						tmppath, path)));
    	unlink(tmppath);
    #else
    	if (rename(tmppath, path) < 0)
    		ereport(ERROR,
    				(errcode_for_file_access(),
    				 errmsg("could not rename file \"%s\" to \"%s\": %m",
    						tmppath, path)));
    #endif
    
    	/* The history file can be archived immediately. */
    	TLHistoryFileName(histfname, newTLI);
    	XLogArchiveNotify(histfname);
    }
    
    /*
     * I/O routines for pg_control
     *
     * *ControlFile is a buffer in shared memory that holds an image of the
     * contents of pg_control.	WriteControlFile() initializes pg_control
     * given a preloaded buffer, ReadControlFile() loads the buffer from
     * the pg_control file (during postmaster or standalone-backend startup),
     * and UpdateControlFile() rewrites pg_control after we modify xlog state.
     *
     * For simplicity, WriteControlFile() initializes the fields of pg_control
     * that are related to checking backend/database compatibility, and
     * ReadControlFile() verifies they are correct.  We could split out the
     * I/O and compatibility-check functions, but there seems no need currently.
     */
    static void
    WriteControlFile(void)
    {
    	int			fd;
    	char		buffer[PG_CONTROL_SIZE];		/* need not be aligned */
    
    	/*
    	 * Initialize version and compatibility-check fields
    	 */
    	ControlFile->pg_control_version = PG_CONTROL_VERSION;
    	ControlFile->catalog_version_no = CATALOG_VERSION_NO;
    
    	ControlFile->maxAlign = MAXIMUM_ALIGNOF;
    	ControlFile->floatFormat = FLOATFORMAT_VALUE;
    
    	ControlFile->blcksz = BLCKSZ;
    	ControlFile->relseg_size = RELSEG_SIZE;
    	ControlFile->xlog_blcksz = XLOG_BLCKSZ;
    	ControlFile->xlog_seg_size = XLOG_SEG_SIZE;
    
    	ControlFile->nameDataLen = NAMEDATALEN;
    	ControlFile->indexMaxKeys = INDEX_MAX_KEYS;
    
    	ControlFile->toast_max_chunk_size = TOAST_MAX_CHUNK_SIZE;
    
    #ifdef HAVE_INT64_TIMESTAMP
    	ControlFile->enableIntTimes = true;
    #else
    	ControlFile->enableIntTimes = false;
    #endif
    	ControlFile->float4ByVal = FLOAT4PASSBYVAL;
    	ControlFile->float8ByVal = FLOAT8PASSBYVAL;
    
    	/* Contents are protected with a CRC */
    	INIT_CRC32(ControlFile->crc);
    	COMP_CRC32(ControlFile->crc,
    			   (char *) ControlFile,
    			   offsetof(ControlFileData, crc));
    	FIN_CRC32(ControlFile->crc);
    
    	/*
    	 * We write out PG_CONTROL_SIZE bytes into pg_control, zero-padding the
    	 * excess over sizeof(ControlFileData).  This reduces the odds of
    	 * premature-EOF errors when reading pg_control.  We'll still fail when we
    	 * check the contents of the file, but hopefully with a more specific
    	 * error than "couldn't read pg_control".
    	 */
    	if (sizeof(ControlFileData) > PG_CONTROL_SIZE)
    		elog(PANIC, "sizeof(ControlFileData) is larger than PG_CONTROL_SIZE; fix either one");
    
    	memset(buffer, 0, PG_CONTROL_SIZE);
    	memcpy(buffer, ControlFile, sizeof(ControlFileData));
    
    	fd = BasicOpenFile(XLOG_CONTROL_FILE,
    					   O_RDWR | O_CREAT | O_EXCL | PG_BINARY,
    					   S_IRUSR | S_IWUSR);
    	if (fd < 0)
    		ereport(PANIC,
    				(errcode_for_file_access(),
    				 errmsg("could not create control file \"%s\": %m",
    						XLOG_CONTROL_FILE)));
    
    	errno = 0;
    	if (write(fd, buffer, PG_CONTROL_SIZE) != PG_CONTROL_SIZE)
    	{
    		/* if write didn't set errno, assume problem is no disk space */
    		if (errno == 0)
    			errno = ENOSPC;
    		ereport(PANIC,
    				(errcode_for_file_access(),
    				 errmsg("could not write to control file: %m")));
    	}
    
    	if (pg_fsync(fd) != 0)
    		ereport(PANIC,
    				(errcode_for_file_access(),
    				 errmsg("could not fsync control file: %m")));
    
    	if (close(fd))
    		ereport(PANIC,
    				(errcode_for_file_access(),
    				 errmsg("could not close control file: %m")));
    }
    
    static void
    ReadControlFile(void)
    {
    	pg_crc32	crc;
    	int			fd;
    
    	/*
    	 * Read data...
    	 */
    	fd = BasicOpenFile(XLOG_CONTROL_FILE,
    					   O_RDWR | PG_BINARY,
    					   S_IRUSR | S_IWUSR);
    	if (fd < 0)
    		ereport(PANIC,
    				(errcode_for_file_access(),
    				 errmsg("could not open control file \"%s\": %m",
    						XLOG_CONTROL_FILE)));
    
    	if (read(fd, ControlFile, sizeof(ControlFileData)) != sizeof(ControlFileData))
    		ereport(PANIC,
    				(errcode_for_file_access(),
    				 errmsg("could not read from control file: %m")));
    
    	close(fd);
    
    	/*
    	 * Check for expected pg_control format version.  If this is wrong, the
    	 * CRC check will likely fail because we'll be checking the wrong number
    	 * of bytes.  Complaining about wrong version will probably be more
    	 * enlightening than complaining about wrong CRC.
    	 */
    
    	if (ControlFile->pg_control_version != PG_CONTROL_VERSION && ControlFile->pg_control_version % 65536 == 0 && ControlFile->pg_control_version / 65536 != 0)
    		ereport(FATAL,
    				(errmsg("database files are incompatible with server"),
    				 errdetail("The database cluster was initialized with PG_CONTROL_VERSION %d (0x%08x),"
    		 " but the server was compiled with PG_CONTROL_VERSION %d (0x%08x).",
    			ControlFile->pg_control_version, ControlFile->pg_control_version,
    						   PG_CONTROL_VERSION, PG_CONTROL_VERSION),
    				 errhint("This could be a problem of mismatched byte ordering.  It looks like you need to initdb.")));
    
    	if (ControlFile->pg_control_version != PG_CONTROL_VERSION)
    		ereport(FATAL,
    				(errmsg("database files are incompatible with server"),
    				 errdetail("The database cluster was initialized with PG_CONTROL_VERSION %d,"
    				  " but the server was compiled with PG_CONTROL_VERSION %d.",
    						ControlFile->pg_control_version, PG_CONTROL_VERSION),
    				 errhint("It looks like you need to initdb.")));
    
    	/* Now check the CRC. */
    	INIT_CRC32(crc);
    	COMP_CRC32(crc,
    			   (char *) ControlFile,
    			   offsetof(ControlFileData, crc));
    	FIN_CRC32(crc);
    
    	if (!EQ_CRC32(crc, ControlFile->crc))
    		ereport(FATAL,
    				(errmsg("incorrect checksum in control file")));
    
    	/*
    	 * Do compatibility checking immediately.  If the database isn't
    	 * compatible with the backend executable, we want to abort before we can
    	 * possibly do any damage.
    	 */
    	if (ControlFile->catalog_version_no != CATALOG_VERSION_NO)
    		ereport(FATAL,
    				(errmsg("database files are incompatible with server"),
    				 errdetail("The database cluster was initialized with CATALOG_VERSION_NO %d,"
    				  " but the server was compiled with CATALOG_VERSION_NO %d.",
    						ControlFile->catalog_version_no, CATALOG_VERSION_NO),
    				 errhint("It looks like you need to initdb.")));
    	if (ControlFile->maxAlign != MAXIMUM_ALIGNOF)
    		ereport(FATAL,
    				(errmsg("database files are incompatible with server"),
    		   errdetail("The database cluster was initialized with MAXALIGN %d,"
    					 " but the server was compiled with MAXALIGN %d.",
    					 ControlFile->maxAlign, MAXIMUM_ALIGNOF),
    				 errhint("It looks like you need to initdb.")));
    	if (ControlFile->floatFormat != FLOATFORMAT_VALUE)
    		ereport(FATAL,
    				(errmsg("database files are incompatible with server"),
    				 errdetail("The database cluster appears to use a different floating-point number format than the server executable."),
    				 errhint("It looks like you need to initdb.")));
    	if (ControlFile->blcksz != BLCKSZ)
    		ereport(FATAL,
    				(errmsg("database files are incompatible with server"),
    			 errdetail("The database cluster was initialized with BLCKSZ %d,"
    					   " but the server was compiled with BLCKSZ %d.",
    					   ControlFile->blcksz, BLCKSZ),
    				 errhint("It looks like you need to recompile or initdb.")));
    	if (ControlFile->relseg_size != RELSEG_SIZE)
    		ereport(FATAL,
    				(errmsg("database files are incompatible with server"),
    		errdetail("The database cluster was initialized with RELSEG_SIZE %d,"
    				  " but the server was compiled with RELSEG_SIZE %d.",
    				  ControlFile->relseg_size, RELSEG_SIZE),
    				 errhint("It looks like you need to recompile or initdb.")));
    	if (ControlFile->xlog_blcksz != XLOG_BLCKSZ)
    		ereport(FATAL,
    				(errmsg("database files are incompatible with server"),
    		errdetail("The database cluster was initialized with XLOG_BLCKSZ %d,"
    				  " but the server was compiled with XLOG_BLCKSZ %d.",
    				  ControlFile->xlog_blcksz, XLOG_BLCKSZ),
    				 errhint("It looks like you need to recompile or initdb.")));
    	if (ControlFile->xlog_seg_size != XLOG_SEG_SIZE)
    		ereport(FATAL,
    				(errmsg("database files are incompatible with server"),
    				 errdetail("The database cluster was initialized with XLOG_SEG_SIZE %d,"
    					   " but the server was compiled with XLOG_SEG_SIZE %d.",
    						   ControlFile->xlog_seg_size, XLOG_SEG_SIZE),
    				 errhint("It looks like you need to recompile or initdb.")));
    	if (ControlFile->nameDataLen != NAMEDATALEN)
    		ereport(FATAL,
    				(errmsg("database files are incompatible with server"),
    		errdetail("The database cluster was initialized with NAMEDATALEN %d,"
    				  " but the server was compiled with NAMEDATALEN %d.",
    				  ControlFile->nameDataLen, NAMEDATALEN),
    				 errhint("It looks like you need to recompile or initdb.")));
    	if (ControlFile->indexMaxKeys != INDEX_MAX_KEYS)
    		ereport(FATAL,
    				(errmsg("database files are incompatible with server"),
    				 errdetail("The database cluster was initialized with INDEX_MAX_KEYS %d,"
    					  " but the server was compiled with INDEX_MAX_KEYS %d.",
    						   ControlFile->indexMaxKeys, INDEX_MAX_KEYS),
    				 errhint("It looks like you need to recompile or initdb.")));
    	if (ControlFile->toast_max_chunk_size != TOAST_MAX_CHUNK_SIZE)
    		ereport(FATAL,
    				(errmsg("database files are incompatible with server"),
    				 errdetail("The database cluster was initialized with TOAST_MAX_CHUNK_SIZE %d,"
    				" but the server was compiled with TOAST_MAX_CHUNK_SIZE %d.",
    			  ControlFile->toast_max_chunk_size, (int) TOAST_MAX_CHUNK_SIZE),
    				 errhint("It looks like you need to recompile or initdb.")));
    
    #ifdef HAVE_INT64_TIMESTAMP
    	if (ControlFile->enableIntTimes != true)
    		ereport(FATAL,
    				(errmsg("database files are incompatible with server"),
    				 errdetail("The database cluster was initialized without HAVE_INT64_TIMESTAMP"
    				  " but the server was compiled with HAVE_INT64_TIMESTAMP."),
    				 errhint("It looks like you need to recompile or initdb.")));
    #else
    	if (ControlFile->enableIntTimes != false)
    		ereport(FATAL,
    				(errmsg("database files are incompatible with server"),
    				 errdetail("The database cluster was initialized with HAVE_INT64_TIMESTAMP"
    			   " but the server was compiled without HAVE_INT64_TIMESTAMP."),
    				 errhint("It looks like you need to recompile or initdb.")));
    #endif
    
    #ifdef USE_FLOAT4_BYVAL
    	if (ControlFile->float4ByVal != true)
    		ereport(FATAL,
    				(errmsg("database files are incompatible with server"),
    				 errdetail("The database cluster was initialized without USE_FLOAT4_BYVAL"
    					  " but the server was compiled with USE_FLOAT4_BYVAL."),
    				 errhint("It looks like you need to recompile or initdb.")));
    #else
    	if (ControlFile->float4ByVal != false)
    		ereport(FATAL,
    				(errmsg("database files are incompatible with server"),
    		errdetail("The database cluster was initialized with USE_FLOAT4_BYVAL"
    				  " but the server was compiled without USE_FLOAT4_BYVAL."),
    				 errhint("It looks like you need to recompile or initdb.")));
    #endif
    
    #ifdef USE_FLOAT8_BYVAL
    	if (ControlFile->float8ByVal != true)
    		ereport(FATAL,
    				(errmsg("database files are incompatible with server"),
    				 errdetail("The database cluster was initialized without USE_FLOAT8_BYVAL"
    					  " but the server was compiled with USE_FLOAT8_BYVAL."),
    				 errhint("It looks like you need to recompile or initdb.")));
    #else
    	if (ControlFile->float8ByVal != false)
    		ereport(FATAL,
    				(errmsg("database files are incompatible with server"),
    		errdetail("The database cluster was initialized with USE_FLOAT8_BYVAL"
    				  " but the server was compiled without USE_FLOAT8_BYVAL."),
    				 errhint("It looks like you need to recompile or initdb.")));
    #endif
    }
    
    void
    UpdateControlFile(void)
    {
    	int			fd;
    
    	INIT_CRC32(ControlFile->crc);
    	COMP_CRC32(ControlFile->crc,
    			   (char *) ControlFile,
    			   offsetof(ControlFileData, crc));
    	FIN_CRC32(ControlFile->crc);
    
    	fd = BasicOpenFile(XLOG_CONTROL_FILE,
    					   O_RDWR | PG_BINARY,
    					   S_IRUSR | S_IWUSR);
    	if (fd < 0)
    		ereport(PANIC,
    				(errcode_for_file_access(),
    				 errmsg("could not open control file \"%s\": %m",
    						XLOG_CONTROL_FILE)));
    
    	errno = 0;
    	if (write(fd, ControlFile, sizeof(ControlFileData)) != sizeof(ControlFileData))
    	{
    		/* if write didn't set errno, assume problem is no disk space */
    		if (errno == 0)
    			errno = ENOSPC;
    		ereport(PANIC,
    				(errcode_for_file_access(),
    				 errmsg("could not write to control file: %m")));
    	}
    
    	if (pg_fsync(fd) != 0)
    		ereport(PANIC,
    				(errcode_for_file_access(),
    				 errmsg("could not fsync control file: %m")));
    
    	if (close(fd))
    		ereport(PANIC,
    				(errcode_for_file_access(),
    				 errmsg("could not close control file: %m")));
    }
    
    /*
     * Returns the unique system identifier from control file.
     */
    uint64
    GetSystemIdentifier(void)
    {
    	Assert(ControlFile != NULL);
    	return ControlFile->system_identifier;
    }
    
    /*
     * Initialization of shared memory for XLOG
     */
    Size
    XLOGShmemSize(void)
    {
    	Size		size;
    
    	/* XLogCtl */
    	size = sizeof(XLogCtlData);
    	/* xlblocks array */
    	size = add_size(size, mul_size(sizeof(XLogRecPtr), XLOGbuffers));
    	/* extra alignment padding for XLOG I/O buffers */
    	size = add_size(size, ALIGNOF_XLOG_BUFFER);
    	/* and the buffers themselves */
    	size = add_size(size, mul_size(XLOG_BLCKSZ, XLOGbuffers));
    
    	/*
    	 * Note: we don't count ControlFileData, it comes out of the "slop factor"
    	 * added by CreateSharedMemoryAndSemaphores.  This lets us use this
    	 * routine again below to compute the actual allocation size.
    	 */
    
    	return size;
    }
    
    void
    XLOGShmemInit(void)
    {
    	bool		foundCFile,
    				foundXLog;
    	char	   *allocptr;
    
    	ControlFile = (ControlFileData *)
    		ShmemInitStruct("Control File", sizeof(ControlFileData), &foundCFile);
    	XLogCtl = (XLogCtlData *)
    		ShmemInitStruct("XLOG Ctl", XLOGShmemSize(), &foundXLog);
    
    	if (foundCFile || foundXLog)
    	{
    		/* both should be present or neither */
    		Assert(foundCFile && foundXLog);
    		return;
    	}
    
    	memset(XLogCtl, 0, sizeof(XLogCtlData));
    
    	/*
    	 * Since XLogCtlData contains XLogRecPtr fields, its sizeof should be a
    	 * multiple of the alignment for same, so no extra alignment padding is
    	 * needed here.
    	 */
    	allocptr = ((char *) XLogCtl) + sizeof(XLogCtlData);
    	XLogCtl->xlblocks = (XLogRecPtr *) allocptr;
    	memset(XLogCtl->xlblocks, 0, sizeof(XLogRecPtr) * XLOGbuffers);
    	allocptr += sizeof(XLogRecPtr) * XLOGbuffers;
    
    	/*
    	 * Align the start of the page buffers to an ALIGNOF_XLOG_BUFFER boundary.
    	 */
    	allocptr = (char *) TYPEALIGN(ALIGNOF_XLOG_BUFFER, allocptr);
    	XLogCtl->pages = allocptr;
    	memset(XLogCtl->pages, 0, (Size) XLOG_BLCKSZ * XLOGbuffers);
    
    	/*
    	 * Do basic initialization of XLogCtl shared data. (StartupXLOG will fill
    	 * in additional info.)
    	 */
    	XLogCtl->XLogCacheBlck = XLOGbuffers - 1;
    	XLogCtl->SharedRecoveryInProgress = true;
    	XLogCtl->Insert.currpage = (XLogPageHeader) (XLogCtl->pages);
    	SpinLockInit(&XLogCtl->info_lck);
    
    	/*
    	 * If we are not in bootstrap mode, pg_control should already exist. Read
    	 * and validate it immediately (see comments in ReadControlFile() for the
    	 * reasons why).
    	 */
    	if (!IsBootstrapProcessingMode())
    		ReadControlFile();
    }
    
    /*
     * This func must be called ONCE on system install.  It creates pg_control
     * and the initial XLOG segment.
     */
    void
    BootStrapXLOG(void)
    {
    	CheckPoint	checkPoint;
    	char	   *buffer;
    	XLogPageHeader page;
    	XLogLongPageHeader longpage;
    	XLogRecord *record;
    	bool		use_existent;
    	uint64		sysidentifier;
    	struct timeval tv;
    	pg_crc32	crc;
    
    	/*
    	 * Select a hopefully-unique system identifier code for this installation.
    	 * We use the result of gettimeofday(), including the fractional seconds
    	 * field, as being about as unique as we can easily get.  (Think not to
    	 * use random(), since it hasn't been seeded and there's no portable way
    	 * to seed it other than the system clock value...)  The upper half of the
    	 * uint64 value is just the tv_sec part, while the lower half is the XOR
    	 * of tv_sec and tv_usec.  This is to ensure that we don't lose uniqueness
    	 * unnecessarily if "uint64" is really only 32 bits wide.  A person
    	 * knowing this encoding can determine the initialization time of the
    	 * installation, which could perhaps be useful sometimes.
    	 */
    	gettimeofday(&tv, NULL);
    	sysidentifier = ((uint64) tv.tv_sec) << 32;
    	sysidentifier |= (uint32) (tv.tv_sec | tv.tv_usec);
    
    	/* First timeline ID is always 1 */
    	ThisTimeLineID = 1;
    
    	/* page buffer must be aligned suitably for O_DIRECT */
    	buffer = (char *) palloc(XLOG_BLCKSZ + ALIGNOF_XLOG_BUFFER);
    	page = (XLogPageHeader) TYPEALIGN(ALIGNOF_XLOG_BUFFER, buffer);
    	memset(page, 0, XLOG_BLCKSZ);
    
    	/* Set up information for the initial checkpoint record */
    	checkPoint.redo.xlogid = 0;
    	checkPoint.redo.xrecoff = SizeOfXLogLongPHD;
    	checkPoint.ThisTimeLineID = ThisTimeLineID;
    	checkPoint.nextXidEpoch = 0;
    	checkPoint.nextXid = FirstNormalTransactionId;
    	checkPoint.nextOid = FirstBootstrapObjectId;
    	checkPoint.nextMulti = FirstMultiXactId;
    	checkPoint.nextMultiOffset = 0;
    	checkPoint.oldestXid = FirstNormalTransactionId;
    	checkPoint.oldestXidDB = TemplateDbOid;
    	checkPoint.time = (pg_time_t) time(NULL);
    	checkPoint.oldestActiveXid = InvalidTransactionId;
    
    	ShmemVariableCache->nextXid = checkPoint.nextXid;
    	ShmemVariableCache->nextOid = checkPoint.nextOid;
    	ShmemVariableCache->oidCount = 0;
    	MultiXactSetNextMXact(checkPoint.nextMulti, checkPoint.nextMultiOffset);
    	SetTransactionIdLimit(checkPoint.oldestXid, checkPoint.oldestXidDB);
    
    	/* Set up the XLOG page header */
    	page->xlp_magic = XLOG_PAGE_MAGIC;
    	page->xlp_info = XLP_LONG_HEADER;
    	page->xlp_tli = ThisTimeLineID;
    	page->xlp_pageaddr.xlogid = 0;
    	page->xlp_pageaddr.xrecoff = 0;
    	longpage = (XLogLongPageHeader) page;
    	longpage->xlp_sysid = sysidentifier;
    	longpage->xlp_seg_size = XLogSegSize;
    	longpage->xlp_xlog_blcksz = XLOG_BLCKSZ;
    
    	/* Insert the initial checkpoint record */
    	record = (XLogRecord *) ((char *) page + SizeOfXLogLongPHD);
    	record->xl_prev.xlogid = 0;
    	record->xl_prev.xrecoff = 0;
    	record->xl_xid = InvalidTransactionId;
    	record->xl_tot_len = SizeOfXLogRecord + sizeof(checkPoint);
    	record->xl_len = sizeof(checkPoint);
    	record->xl_info = XLOG_CHECKPOINT_SHUTDOWN;
    	record->xl_rmid = RM_XLOG_ID;
    	memcpy(XLogRecGetData(record), &checkPoint, sizeof(checkPoint));
    
    	INIT_CRC32(crc);
    	COMP_CRC32(crc, &checkPoint, sizeof(checkPoint));
    	COMP_CRC32(crc, (char *) record + sizeof(pg_crc32),
    			   SizeOfXLogRecord - sizeof(pg_crc32));
    	FIN_CRC32(crc);
    	record->xl_crc = crc;
    
    	/* Create first XLOG segment file */
    	use_existent = false;
    	openLogFile = XLogFileInit(0, 0, &use_existent, false);
    
    	/* Write the first page with the initial record */
    	errno = 0;
    	if (write(openLogFile, page, XLOG_BLCKSZ) != XLOG_BLCKSZ)
    	{
    		/* if write didn't set errno, assume problem is no disk space */
    		if (errno == 0)
    			errno = ENOSPC;
    		ereport(PANIC,
    				(errcode_for_file_access(),
    			  errmsg("could not write bootstrap transaction log file: %m")));
    	}
    
    	if (pg_fsync(openLogFile) != 0)
    		ereport(PANIC,
    				(errcode_for_file_access(),
    			  errmsg("could not fsync bootstrap transaction log file: %m")));
    
    	if (close(openLogFile))
    		ereport(PANIC,
    				(errcode_for_file_access(),
    			  errmsg("could not close bootstrap transaction log file: %m")));
    
    	openLogFile = -1;
    
    	/* Now create pg_control */
    
    	memset(ControlFile, 0, sizeof(ControlFileData));
    	/* Initialize pg_control status fields */
    	ControlFile->system_identifier = sysidentifier;
    	ControlFile->state = DB_SHUTDOWNED;
    	ControlFile->time = checkPoint.time;
    	ControlFile->checkPoint = checkPoint.redo;
    	ControlFile->checkPointCopy = checkPoint;
    	/* some additional ControlFile fields are set in WriteControlFile() */
    
    	WriteControlFile();
    
    	/* Bootstrap the commit log, too */
    	BootStrapCLOG();
    	BootStrapSUBTRANS();
    	BootStrapMultiXact();
    
    	pfree(buffer);
    }
    
    static char *
    str_time(pg_time_t tnow)
    {
    	static char buf[128];
    
    	pg_strftime(buf, sizeof(buf),
    				"%Y-%m-%d %H:%M:%S %Z",
    				pg_localtime(&tnow, log_timezone));
    
    	return buf;
    }
    
    /*
     * See if there is a recovery command file (recovery.conf), and if so
     * read in parameters for archive recovery and XLOG streaming.
     *
     * XXX longer term intention is to expand this to
     * cater for additional parameters and controls
     * possibly use a flex lexer similar to the GUC one
     */
    static void
    readRecoveryCommandFile(void)
    {
    	FILE	   *fd;
    	char		cmdline[MAXPGPATH];
    	TimeLineID	rtli = 0;
    	bool		rtliGiven = false;
    	bool		syntaxError = false;
    
    	fd = AllocateFile(RECOVERY_COMMAND_FILE, "r");
    	if (fd == NULL)
    	{
    		if (errno == ENOENT)
    			return;				/* not there, so no archive recovery */
    		ereport(FATAL,
    				(errcode_for_file_access(),
    				 errmsg("could not open recovery command file \"%s\": %m",
    						RECOVERY_COMMAND_FILE)));
    	}
    
    	/*
    	 * Parse the file...
    	 */
    	while (fgets(cmdline, sizeof(cmdline), fd) != NULL)
    	{
    		/* skip leading whitespace and check for # comment */
    		char	   *ptr;
    		char	   *tok1;
    		char	   *tok2;
    
    		for (ptr = cmdline; *ptr; ptr++)
    		{
    			if (!isspace((unsigned char) *ptr))
    				break;
    		}
    		if (*ptr == '\0' || *ptr == '#')
    			continue;
    
    		/* identify the quoted parameter value */
    		tok1 = strtok(ptr, "'");
    		if (!tok1)
    		{
    			syntaxError = true;
    			break;
    		}
    		tok2 = strtok(NULL, "'");
    		if (!tok2)
    		{
    			syntaxError = true;
    			break;
    		}
    		/* reparse to get just the parameter name */
    		tok1 = strtok(ptr, " \t=");
    		if (!tok1)
    		{
    			syntaxError = true;
    			break;
    		}
    
    		if (strcmp(tok1, "restore_command") == 0)
    		{
    			recoveryRestoreCommand = pstrdup(tok2);
    			ereport(DEBUG2,
    					(errmsg("restore_command = '%s'",
    							recoveryRestoreCommand)));
    		}
    		else if (strcmp(tok1, "recovery_end_command") == 0)
    		{
    			recoveryEndCommand = pstrdup(tok2);
    			ereport(DEBUG2,
    					(errmsg("recovery_end_command = '%s'",
    							recoveryEndCommand)));
    		}
    		else if (strcmp(tok1, "restartpoint_command") == 0)
    		{
    			restartPointCommand = pstrdup(tok2);
    			ereport(DEBUG2,
    					(errmsg("restartpoint_command = '%s'",
    							restartPointCommand)));
    		}
    		else if (strcmp(tok1, "recovery_target_timeline") == 0)
    		{
    			rtliGiven = true;
    			if (strcmp(tok2, "latest") == 0)
    				rtli = 0;
    			else
    			{
    				errno = 0;
    				rtli = (TimeLineID) strtoul(tok2, NULL, 0);
    				if (errno == EINVAL || errno == ERANGE)
    					ereport(FATAL,
    							(errmsg("recovery_target_timeline is not a valid number: \"%s\"",
    									tok2)));
    			}
    			if (rtli)
    				ereport(DEBUG2,
    						(errmsg("recovery_target_timeline = %u", rtli)));
    			else
    				ereport(DEBUG2,
    						(errmsg("recovery_target_timeline = latest")));
    		}
    		else if (strcmp(tok1, "recovery_target_xid") == 0)
    		{
    			errno = 0;
    			recoveryTargetXid = (TransactionId) strtoul(tok2, NULL, 0);
    			if (errno == EINVAL || errno == ERANGE)
    				ereport(FATAL,
    				 (errmsg("recovery_target_xid is not a valid number: \"%s\"",
    						 tok2)));
    			ereport(DEBUG2,
    					(errmsg("recovery_target_xid = %u",
    							recoveryTargetXid)));
    			recoveryTarget = true;
    			recoveryTargetExact = true;
    		}
    		else if (strcmp(tok1, "recovery_target_time") == 0)
    		{
    			/*
    			 * if recovery_target_xid specified, then this overrides
    			 * recovery_target_time
    			 */
    			if (recoveryTargetExact)
    				continue;
    			recoveryTarget = true;
    			recoveryTargetExact = false;
    
    			/*
    			 * Convert the time string given by the user to TimestampTz form.
    			 */
    			recoveryTargetTime =
    				DatumGetTimestampTz(DirectFunctionCall3(timestamptz_in,
    														CStringGetDatum(tok2),
    												ObjectIdGetDatum(InvalidOid),
    														Int32GetDatum(-1)));
    			ereport(DEBUG2,
    					(errmsg("recovery_target_time = '%s'",
    							timestamptz_to_str(recoveryTargetTime))));
    		}
    		else if (strcmp(tok1, "recovery_target_inclusive") == 0)
    		{
    			/*
    			 * does nothing if a recovery_target is not also set
    			 */
    			if (!parse_bool(tok2, &recoveryTargetInclusive))
    				ereport(ERROR,
    						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
    						 errmsg("parameter \"recovery_target_inclusive\" requires a Boolean value")));
    			ereport(DEBUG2,
    					(errmsg("recovery_target_inclusive = %s", tok2)));
    		}
    		else if (strcmp(tok1, "standby_mode") == 0)
    		{
    			if (!parse_bool(tok2, &StandbyMode))
    				ereport(ERROR,
    						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
    						 errmsg("parameter \"standby_mode\" requires a Boolean value")));
    			ereport(DEBUG2,
    					(errmsg("standby_mode = '%s'", tok2)));
    		}
    		else if (strcmp(tok1, "primary_conninfo") == 0)
    		{
    			PrimaryConnInfo = pstrdup(tok2);
    			ereport(DEBUG2,
    					(errmsg("primary_conninfo = '%s'",
    							PrimaryConnInfo)));
    		}
    		else if (strcmp(tok1, "trigger_file") == 0)
    		{
    			TriggerFile = pstrdup(tok2);
    			ereport(DEBUG2,
    					(errmsg("trigger_file = '%s'",
    							TriggerFile)));
    		}
    		else
    			ereport(FATAL,
    					(errmsg("unrecognized recovery parameter \"%s\"",
    							tok1)));
    	}
    
    	FreeFile(fd);
    
    	if (syntaxError)
    		ereport(FATAL,
    				(errmsg("syntax error in recovery command file: %s",
    						cmdline),
    			  errhint("Lines should have the format parameter = 'value'.")));
    
    	/* If not in standby mode, restore_command must be supplied */
    	if (!StandbyMode && recoveryRestoreCommand == NULL)
    		ereport(FATAL,
    				(errmsg("recovery command file \"%s\" did not specify restore_command nor standby_mode",
    						RECOVERY_COMMAND_FILE)));
    
    	/* Enable fetching from archive recovery area */
    	InArchiveRecovery = true;
    
    	/*
    	 * If user specified recovery_target_timeline, validate it or compute the
    	 * "latest" value.	We can't do this until after we've gotten the restore
    	 * command and set InArchiveRecovery, because we need to fetch timeline
    	 * history files from the archive.
    	 */
    	if (rtliGiven)
    	{
    		if (rtli)
    		{
    			/* Timeline 1 does not have a history file, all else should */
    			if (rtli != 1 && !existsTimeLineHistory(rtli))
    				ereport(FATAL,
    						(errmsg("recovery target timeline %u does not exist",
    								rtli)));
    			recoveryTargetTLI = rtli;
    		}
    		else
    		{
    			/* We start the "latest" search from pg_control's timeline */
    			recoveryTargetTLI = findNewestTimeLine(recoveryTargetTLI);
    		}
    	}
    }
    
    /*
     * Exit archive-recovery state
     */
    static void
    exitArchiveRecovery(TimeLineID endTLI, uint32 endLogId, uint32 endLogSeg)
    {
    	char		recoveryPath[MAXPGPATH];
    	char		xlogpath[MAXPGPATH];
    	XLogRecPtr	InvalidXLogRecPtr = {0, 0};
    
    	/*
    	 * We are no longer in archive recovery state.
    	 */
    	InArchiveRecovery = false;
    
    	/*
    	 * Update min recovery point one last time.
    	 */
    	UpdateMinRecoveryPoint(InvalidXLogRecPtr, true);
    
    	/*
    	 * If the ending log segment is still open, close it (to avoid problems on
    	 * Windows with trying to rename or delete an open file).
    	 */
    	if (readFile >= 0)
    	{
    		close(readFile);
    		readFile = -1;
    	}
    
    	/*
    	 * If the segment was fetched from archival storage, we want to replace
    	 * the existing xlog segment (if any) with the archival version.  This is
    	 * because whatever is in XLOGDIR is very possibly older than what we have
    	 * from the archives, since it could have come from restoring a PGDATA
    	 * backup.	In any case, the archival version certainly is more
    	 * descriptive of what our current database state is, because that is what
    	 * we replayed from.
    	 *
    	 * Note that if we are establishing a new timeline, ThisTimeLineID is
    	 * already set to the new value, and so we will create a new file instead
    	 * of overwriting any existing file.  (This is, in fact, always the case
    	 * at present.)
    	 */
    	snprintf(recoveryPath, MAXPGPATH, XLOGDIR "/RECOVERYXLOG");
    	XLogFilePath(xlogpath, ThisTimeLineID, endLogId, endLogSeg);
    
    	if (restoredFromArchive)
    	{
    		ereport(DEBUG3,
    				(errmsg_internal("moving last restored xlog to \"%s\"",
    								 xlogpath)));
    		unlink(xlogpath);		/* might or might not exist */
    		if (rename(recoveryPath, xlogpath) != 0)
    			ereport(FATAL,
    					(errcode_for_file_access(),
    					 errmsg("could not rename file \"%s\" to \"%s\": %m",
    							recoveryPath, xlogpath)));
    		/* XXX might we need to fix permissions on the file? */
    	}
    	else
    	{
    		/*
    		 * If the latest segment is not archival, but there's still a
    		 * RECOVERYXLOG laying about, get rid of it.
    		 */
    		unlink(recoveryPath);	/* ignore any error */
    
    		/*
    		 * If we are establishing a new timeline, we have to copy data from
    		 * the last WAL segment of the old timeline to create a starting WAL
    		 * segment for the new timeline.
    		 *
    		 * Notify the archiver that the last WAL segment of the old timeline
    		 * is ready to copy to archival storage. Otherwise, it is not archived
    		 * for a while.
    		 */
    		if (endTLI != ThisTimeLineID)
    		{
    			XLogFileCopy(endLogId, endLogSeg,
    						 endTLI, endLogId, endLogSeg);
    
    			if (XLogArchivingActive())
    			{
    				XLogFileName(xlogpath, endTLI, endLogId, endLogSeg);
    				XLogArchiveNotify(xlogpath);
    			}
    		}
    	}
    
    	/*
    	 * Let's just make real sure there are not .ready or .done flags posted
    	 * for the new segment.
    	 */
    	XLogFileName(xlogpath, ThisTimeLineID, endLogId, endLogSeg);
    	XLogArchiveCleanup(xlogpath);
    
    	/* Get rid of any remaining recovered timeline-history file, too */
    	snprintf(recoveryPath, MAXPGPATH, XLOGDIR "/RECOVERYHISTORY");
    	unlink(recoveryPath);		/* ignore any error */
    
    	/*
    	 * Rename the config file out of the way, so that we don't accidentally
    	 * re-enter archive recovery mode in a subsequent crash.
    	 */
    	unlink(RECOVERY_COMMAND_DONE);
    	if (rename(RECOVERY_COMMAND_FILE, RECOVERY_COMMAND_DONE) != 0)
    		ereport(FATAL,
    				(errcode_for_file_access(),
    				 errmsg("could not rename file \"%s\" to \"%s\": %m",
    						RECOVERY_COMMAND_FILE, RECOVERY_COMMAND_DONE)));
    
    	ereport(LOG,
    			(errmsg("archive recovery complete")));
    }
    
    /*
     * For point-in-time recovery, this function decides whether we want to
     * stop applying the XLOG at or after the current record.
     *
     * Returns TRUE if we are stopping, FALSE otherwise.  On TRUE return,
     * *includeThis is set TRUE if we should apply this record before stopping.
     *
     * We also track the timestamp of the latest applied COMMIT/ABORT record
     * in recoveryLastXTime, for logging purposes.
     * Also, some information is saved in recoveryStopXid et al for use in
     * annotating the new timeline's history file.
     */
    static bool
    recoveryStopsHere(XLogRecord *record, bool *includeThis)
    {
    	bool		stopsHere;
    	uint8		record_info;
    	TimestampTz recordXtime;
    
    	/* We only consider stopping at COMMIT or ABORT records */
    	if (record->xl_rmid == RM_XACT_ID)
    	{
    		record_info = record->xl_info & ~XLR_INFO_MASK;
    		if (record_info == XLOG_XACT_COMMIT)
    		{
    			xl_xact_commit *recordXactCommitData;
    
    			recordXactCommitData = (xl_xact_commit *) XLogRecGetData(record);
    			recordXtime = recordXactCommitData->xact_time;
    		}
    		else if (record_info == XLOG_XACT_ABORT)
    		{
    			xl_xact_abort *recordXactAbortData;
    
    			recordXactAbortData = (xl_xact_abort *) XLogRecGetData(record);
    			recordXtime = recordXactAbortData->xact_time;
    		}
    		else
    			return false;
    	}
    	else if (record->xl_rmid == RM_XLOG_ID)
    	{
    		record_info = record->xl_info & ~XLR_INFO_MASK;
    		if (record_info == XLOG_CHECKPOINT_SHUTDOWN ||
    			record_info == XLOG_CHECKPOINT_ONLINE)
    		{
    			CheckPoint	checkPoint;
    
    			memcpy(&checkPoint, XLogRecGetData(record), sizeof(CheckPoint));
    			recoveryLastXTime = checkPoint.time;
    		}
    
    		/*
    		 * We don't want to stop recovery on a checkpoint record, but we do
    		 * want to update recoveryLastXTime. So return is unconditional.
    		 */
    		return false;
    	}
    	else
    		return false;
    
    	/* Do we have a PITR target at all? */
    	if (!recoveryTarget)
    	{
    		recoveryLastXTime = recordXtime;
    		return false;
    	}
    
    	if (recoveryTargetExact)
    	{
    		/*
    		 * there can be only one transaction end record with this exact
    		 * transactionid
    		 *
    		 * when testing for an xid, we MUST test for equality only, since
    		 * transactions are numbered in the order they start, not the order
    		 * they complete. A higher numbered xid will complete before you about
    		 * 50% of the time...
    		 */
    		stopsHere = (record->xl_xid == recoveryTargetXid);
    		if (stopsHere)
    			*includeThis = recoveryTargetInclusive;
    	}
    	else
    	{
    		/*
    		 * there can be many transactions that share the same commit time, so
    		 * we stop after the last one, if we are inclusive, or stop at the
    		 * first one if we are exclusive
    		 */
    		if (recoveryTargetInclusive)
    			stopsHere = (recordXtime > recoveryTargetTime);
    		else
    			stopsHere = (recordXtime >= recoveryTargetTime);
    		if (stopsHere)
    			*includeThis = false;
    	}
    
    	if (stopsHere)
    	{
    		recoveryStopXid = record->xl_xid;
    		recoveryStopTime = recordXtime;
    		recoveryStopAfter = *includeThis;
    
    		if (record_info == XLOG_XACT_COMMIT)
    		{
    			if (recoveryStopAfter)
    				ereport(LOG,
    						(errmsg("recovery stopping after commit of transaction %u, time %s",
    								recoveryStopXid,
    								timestamptz_to_str(recoveryStopTime))));
    			else
    				ereport(LOG,
    						(errmsg("recovery stopping before commit of transaction %u, time %s",
    								recoveryStopXid,
    								timestamptz_to_str(recoveryStopTime))));
    		}
    		else
    		{
    			if (recoveryStopAfter)
    				ereport(LOG,
    						(errmsg("recovery stopping after abort of transaction %u, time %s",
    								recoveryStopXid,
    								timestamptz_to_str(recoveryStopTime))));
    			else
    				ereport(LOG,
    						(errmsg("recovery stopping before abort of transaction %u, time %s",
    								recoveryStopXid,
    								timestamptz_to_str(recoveryStopTime))));
    		}
    
    		if (recoveryStopAfter)
    			recoveryLastXTime = recordXtime;
    	}
    	else
    		recoveryLastXTime = recordXtime;
    
    	return stopsHere;
    }
    
    /*
     * Returns bool with current recovery mode, a global state.
     */
    Datum
    pg_is_in_recovery(PG_FUNCTION_ARGS)
    {
    	PG_RETURN_BOOL(RecoveryInProgress());
    }
    
    /*
     * Returns timestamp of last recovered commit/abort record.
     */
    TimestampTz
    GetLatestXLogTime(void)
    {
    	/* use volatile pointer to prevent code rearrangement */
    	volatile XLogCtlData *xlogctl = XLogCtl;
    
    	SpinLockAcquire(&xlogctl->info_lck);
    	recoveryLastXTime = xlogctl->recoveryLastXTime;
    	SpinLockRelease(&xlogctl->info_lck);
    
    	return recoveryLastXTime;
    }
    
    /*
     * Note that text field supplied is a parameter name and does not require translation
     */
    #define RecoveryRequiresIntParameter(param_name, currValue, checkpointValue) \
    { \
    	if (currValue < checkpointValue) \
    		ereport(ERROR, \
    			(errmsg("recovery connections cannot continue because " \
    					"%s = %u is a lower setting than on WAL source server (value was %u)", \
    					param_name, \
    					currValue, \
    					checkpointValue))); \
    }
    
    /*
     * Check to see if required parameters are set high enough on this server
     * for various aspects of recovery operation.
     */
    static void
    CheckRequiredParameterValues(CheckPoint checkPoint)
    {
    	/* We ignore autovacuum_max_workers when we make this test. */
    	RecoveryRequiresIntParameter("max_connections",
    								 MaxConnections, checkPoint.MaxConnections);
    
    	RecoveryRequiresIntParameter("max_prepared_xacts",
    						  max_prepared_xacts, checkPoint.max_prepared_xacts);
    	RecoveryRequiresIntParameter("max_locks_per_xact",
    						  max_locks_per_xact, checkPoint.max_locks_per_xact);
    
    	if (!checkPoint.XLogStandbyInfoMode)
    		ereport(ERROR,
    				(errmsg("recovery connections cannot start because the recovery_connections "
    						"parameter is disabled on the WAL source server")));
    }
    
    /*
     * This must be called ONCE during postmaster or standalone-backend startup
     */
    void
    StartupXLOG(void)
    {
    	XLogCtlInsert *Insert;
    	CheckPoint	checkPoint;
    	bool		wasShutdown;
    	bool		reachedStopPoint = false;
    	bool		haveBackupLabel = false;
    	XLogRecPtr	RecPtr,
    				checkPointLoc,
    				EndOfLog;
    	uint32		endLogId;
    	uint32		endLogSeg;
    	XLogRecord *record;
    	uint32		freespace;
    	TransactionId oldestActiveXID;
    	bool		bgwriterLaunched = false;
    	bool		backendsAllowed = false;
    
    	/*
    	 * Read control file and check XLOG status looks valid.
    	 *
    	 * Note: in most control paths, *ControlFile is already valid and we need
    	 * not do ReadControlFile() here, but might as well do it to be sure.
    	 */
    	ReadControlFile();
    
    	if (ControlFile->state < DB_SHUTDOWNED ||
    		ControlFile->state > DB_IN_PRODUCTION ||
    		!XRecOffIsValid(ControlFile->checkPoint.xrecoff))
    		ereport(FATAL,
    				(errmsg("control file contains invalid data")));
    
    	if (ControlFile->state == DB_SHUTDOWNED)
    		ereport(LOG,
    				(errmsg("database system was shut down at %s",
    						str_time(ControlFile->time))));
    	else if (ControlFile->state == DB_SHUTDOWNING)
    		ereport(LOG,
    				(errmsg("database system shutdown was interrupted; last known up at %s",
    						str_time(ControlFile->time))));
    	else if (ControlFile->state == DB_IN_CRASH_RECOVERY)
    		ereport(LOG,
    		   (errmsg("database system was interrupted while in recovery at %s",
    				   str_time(ControlFile->time)),
    			errhint("This probably means that some data is corrupted and"
    					" you will have to use the last backup for recovery.")));
    	else if (ControlFile->state == DB_IN_ARCHIVE_RECOVERY)
    		ereport(LOG,
    				(errmsg("database system was interrupted while in recovery at log time %s",
    						str_time(ControlFile->checkPointCopy.time)),
    				 errhint("If this has occurred more than once some data might be corrupted"
    			  " and you might need to choose an earlier recovery target.")));
    	else if (ControlFile->state == DB_IN_PRODUCTION)
    		ereport(LOG,
    			  (errmsg("database system was interrupted; last known up at %s",
    					  str_time(ControlFile->time))));
    
    	/* This is just to allow attaching to startup process with a debugger */
    #ifdef XLOG_REPLAY_DELAY
    	if (ControlFile->state != DB_SHUTDOWNED)
    		pg_usleep(60000000L);
    #endif
    
    	/*
    	 * Verify that pg_xlog and pg_xlog/archive_status exist.  In cases where
    	 * someone has performed a copy for PITR, these directories may have been
    	 * excluded and need to be re-created.
    	 */
    	ValidateXLOGDirectoryStructure();
    
    	/*
    	 * Clear out any old relcache cache files.	This is *necessary* if we do
    	 * any WAL replay, since that would probably result in the cache files
    	 * being out of sync with database reality.  In theory we could leave them
    	 * in place if the database had been cleanly shut down, but it seems
    	 * safest to just remove them always and let them be rebuilt during the
    	 * first backend startup.
    	 */
    	RelationCacheInitFileRemove();
    
    	/*
    	 * Initialize on the assumption we want to recover to the same timeline
    	 * that's active according to pg_control.
    	 */
    	recoveryTargetTLI = ControlFile->checkPointCopy.ThisTimeLineID;
    
    	/*
    	 * Check for recovery control file, and if so set up state for offline
    	 * recovery
    	 */
    	readRecoveryCommandFile();
    
    	/* Now we can determine the list of expected TLIs */
    	expectedTLIs = readTimeLineHistory(recoveryTargetTLI);
    
    	/*
    	 * If pg_control's timeline is not in expectedTLIs, then we cannot
    	 * proceed: the backup is not part of the history of the requested
    	 * timeline.
    	 */
    	if (!list_member_int(expectedTLIs,
    						 (int) ControlFile->checkPointCopy.ThisTimeLineID))
    		ereport(FATAL,
    				(errmsg("requested timeline %u is not a child of database system timeline %u",
    						recoveryTargetTLI,
    						ControlFile->checkPointCopy.ThisTimeLineID)));
    
    	/*
    	 * Save the selected recovery target timeline ID and restartpoint_command
    	 * in shared memory so that other processes can see them
    	 */
    	XLogCtl->RecoveryTargetTLI = recoveryTargetTLI;
    	strncpy(XLogCtl->restartPointCommand,
    			restartPointCommand ? restartPointCommand : "",
    			sizeof(XLogCtl->restartPointCommand));
    
    	if (read_backup_label(&checkPointLoc))
    	{
    		/*
    		 * When a backup_label file is present, we want to roll forward from
    		 * the checkpoint it identifies, rather than using pg_control.
    		 */
    		record = ReadCheckpointRecord(checkPointLoc, 0);
    		if (record != NULL)
    		{
    			ereport(DEBUG1,
    					(errmsg("checkpoint record is at %X/%X",
    							checkPointLoc.xlogid, checkPointLoc.xrecoff)));
    			InRecovery = true;	/* force recovery even if SHUTDOWNED */
    		}
    		else
    		{
    			ereport(PANIC,
    					(errmsg("could not locate required checkpoint record"),
    					 errhint("If you are not restoring from a backup, try removing the file \"%s/backup_label\".", DataDir)));
    		}
    		/* set flag to delete it later */
    		haveBackupLabel = true;
    	}
    	else
    	{
    		/*
    		 * Get the last valid checkpoint record.  If the latest one according
    		 * to pg_control is broken, try the next-to-last one.
    		 */
    		checkPointLoc = ControlFile->checkPoint;
    		RedoStartLSN = ControlFile->checkPointCopy.redo;
    		record = ReadCheckpointRecord(checkPointLoc, 1);
    		if (record != NULL)
    		{
    			ereport(DEBUG1,
    					(errmsg("checkpoint record is at %X/%X",
    							checkPointLoc.xlogid, checkPointLoc.xrecoff)));
    		}
    		else if (StandbyMode)
    		{
    			/*
    			 * The last valid checkpoint record required for a streaming
    			 * recovery exists in neither standby nor the primary.
    			 */
    			ereport(PANIC,
    					(errmsg("could not locate a valid checkpoint record")));
    		}
    		else
    		{
    			checkPointLoc = ControlFile->prevCheckPoint;
    			record = ReadCheckpointRecord(checkPointLoc, 2);
    			if (record != NULL)
    			{
    				ereport(LOG,
    						(errmsg("using previous checkpoint record at %X/%X",
    							  checkPointLoc.xlogid, checkPointLoc.xrecoff)));
    				InRecovery = true;		/* force recovery even if SHUTDOWNED */
    			}
    			else
    				ereport(PANIC,
    					 (errmsg("could not locate a valid checkpoint record")));
    		}
    	}
    
    	LastRec = RecPtr = checkPointLoc;
    	memcpy(&checkPoint, XLogRecGetData(record), sizeof(CheckPoint));
    	wasShutdown = (record->xl_info == XLOG_CHECKPOINT_SHUTDOWN);
    
    	ereport(DEBUG1,
    			(errmsg("redo record is at %X/%X; shutdown %s",
    					checkPoint.redo.xlogid, checkPoint.redo.xrecoff,
    					wasShutdown ? "TRUE" : "FALSE")));
    	ereport(DEBUG1,
    			(errmsg("next transaction ID: %u/%u; next OID: %u",
    					checkPoint.nextXidEpoch, checkPoint.nextXid,
    					checkPoint.nextOid)));
    	ereport(DEBUG1,
    			(errmsg("next MultiXactId: %u; next MultiXactOffset: %u",
    					checkPoint.nextMulti, checkPoint.nextMultiOffset)));
    	ereport(DEBUG1,
    			(errmsg("oldest unfrozen transaction ID: %u, in database %u",
    					checkPoint.oldestXid, checkPoint.oldestXidDB)));
    	if (!TransactionIdIsNormal(checkPoint.nextXid))
    		ereport(PANIC,
    				(errmsg("invalid next transaction ID")));
    
    	ShmemVariableCache->nextXid = checkPoint.nextXid;
    	ShmemVariableCache->nextOid = checkPoint.nextOid;
    	ShmemVariableCache->oidCount = 0;
    	MultiXactSetNextMXact(checkPoint.nextMulti, checkPoint.nextMultiOffset);
    	SetTransactionIdLimit(checkPoint.oldestXid, checkPoint.oldestXidDB);
    
    	/*
    	 * We must replay WAL entries using the same TimeLineID they were created
    	 * under, so temporarily adopt the TLI indicated by the checkpoint (see
    	 * also xlog_redo()).
    	 */
    	ThisTimeLineID = checkPoint.ThisTimeLineID;
    
    	RedoRecPtr = XLogCtl->Insert.RedoRecPtr = checkPoint.redo;
    
    	if (XLByteLT(RecPtr, checkPoint.redo))
    		ereport(PANIC,
    				(errmsg("invalid redo in checkpoint record")));
    
    	/*
    	 * Check whether we need to force recovery from WAL.  If it appears to
    	 * have been a clean shutdown and we did not have a recovery.conf file,
    	 * then assume no recovery needed.
    	 */
    	if (XLByteLT(checkPoint.redo, RecPtr))
    	{
    		if (wasShutdown)
    			ereport(PANIC,
    					(errmsg("invalid redo record in shutdown checkpoint")));
    		InRecovery = true;
    	}
    	else if (ControlFile->state != DB_SHUTDOWNED)
    		InRecovery = true;
    	else if (InArchiveRecovery)
    	{
    		/* force recovery due to presence of recovery.conf */
    		InRecovery = true;
    	}
    
    	/* REDO */
    	if (InRecovery)
    	{
    		int			rmid;
    
    		/*
    		 * Update pg_control to show that we are recovering and to show the
    		 * selected checkpoint as the place we are starting from. We also mark
    		 * pg_control with any minimum recovery stop point obtained from a
    		 * backup history file.
    		 */
    		if (InArchiveRecovery)
    		{
    			if (StandbyMode)
    				ereport(LOG,
    						(errmsg("entering standby mode")));
    			else if (recoveryTarget)
    			{
    				if (recoveryTargetExact)
    					ereport(LOG,
    						 (errmsg("starting point-in-time recovery to XID %u",
    								 recoveryTargetXid)));
    				else
    					ereport(LOG,
    							(errmsg("starting point-in-time recovery to %s",
    									timestamptz_to_str(recoveryTargetTime))));
    			}
    			else
    				ereport(LOG,
    						(errmsg("starting archive recovery")));
    			ControlFile->state = DB_IN_ARCHIVE_RECOVERY;
    		}
    		else
    		{
    			ereport(LOG,
    					(errmsg("database system was not properly shut down; "
    							"automatic recovery in progress")));
    			ControlFile->state = DB_IN_CRASH_RECOVERY;
    		}
    		ControlFile->prevCheckPoint = ControlFile->checkPoint;
    		ControlFile->checkPoint = checkPointLoc;
    		ControlFile->checkPointCopy = checkPoint;
    		if (InArchiveRecovery)
    		{
    			/* initialize minRecoveryPoint if not set yet */
    			if (XLByteLT(ControlFile->minRecoveryPoint, checkPoint.redo))
    				ControlFile->minRecoveryPoint = checkPoint.redo;
    		}
    
    		/*
    		 * set backupStartupPoint if we're starting archive recovery from a
    		 * base backup
    		 */
    		if (haveBackupLabel)
    			ControlFile->backupStartPoint = checkPoint.redo;
    		ControlFile->time = (pg_time_t) time(NULL);
    		/* No need to hold ControlFileLock yet, we aren't up far enough */
    		UpdateControlFile();
    
    		/* initialize our local copy of minRecoveryPoint */
    		minRecoveryPoint = ControlFile->minRecoveryPoint;
    
    		/*
    		 * Reset pgstat data, because it may be invalid after recovery.
    		 */
    		pgstat_reset_all();
    
    		/*
    		 * If there was a backup label file, it's done its job and the info
    		 * has now been propagated into pg_control.  We must get rid of the
    		 * label file so that if we crash during recovery, we'll pick up at
    		 * the latest recovery restartpoint instead of going all the way back
    		 * to the backup start point.  It seems prudent though to just rename
    		 * the file out of the way rather than delete it completely.
    		 */
    		if (haveBackupLabel)
    		{
    			unlink(BACKUP_LABEL_OLD);
    			if (rename(BACKUP_LABEL_FILE, BACKUP_LABEL_OLD) != 0)
    				ereport(FATAL,
    						(errcode_for_file_access(),
    						 errmsg("could not rename file \"%s\" to \"%s\": %m",
    								BACKUP_LABEL_FILE, BACKUP_LABEL_OLD)));
    		}
    
    		/*
    		 * Initialize recovery connections, if enabled. We won't let backends
    		 * in yet, not until we've reached the min recovery point specified in
    		 * control file and we've established a recovery snapshot from a
    		 * running-xacts WAL record.
    		 */
    		if (InArchiveRecovery && XLogRequestRecoveryConnections)
    		{
    			TransactionId *xids;
    			int			nxids;
    
    			CheckRequiredParameterValues(checkPoint);
    
    			ereport(DEBUG1,
    					(errmsg("initializing recovery connections")));
    
    			InitRecoveryTransactionEnvironment();
    
    			if (wasShutdown)
    				oldestActiveXID = PrescanPreparedTransactions(&xids, &nxids);
    			else
    				oldestActiveXID = checkPoint.oldestActiveXid;
    			Assert(TransactionIdIsValid(oldestActiveXID));
    
    			/* Startup commit log and related stuff */
    			StartupCLOG();
    			StartupSUBTRANS(oldestActiveXID);
    			StartupMultiXact();
    
    			ProcArrayInitRecoveryInfo(oldestActiveXID);
    		}
    
    		/* Initialize resource managers */
    		for (rmid = 0; rmid <= RM_MAX_ID; rmid++)
    		{
    			if (RmgrTable[rmid].rm_startup != NULL)
    				RmgrTable[rmid].rm_startup();
    		}
    
    		/*
    		 * Find the first record that logically follows the checkpoint --- it
    		 * might physically precede it, though.
    		 */
    		if (XLByteLT(checkPoint.redo, RecPtr))
    		{
    			/* back up to find the record */
    			record = ReadRecord(&(checkPoint.redo), PANIC, false);
    		}
    		else
    		{
    			/* just have to read next record after CheckPoint */
    			record = ReadRecord(NULL, LOG, false);
    		}
    
    		if (record != NULL)
    		{
    			bool		recoveryContinue = true;
    			bool		recoveryApply = true;
    			bool		reachedMinRecoveryPoint = false;
    			ErrorContextCallback errcontext;
    
    			/* use volatile pointer to prevent code rearrangement */
    			volatile XLogCtlData *xlogctl = XLogCtl;
    
    			/* initialize shared replayEndRecPtr and recoveryLastRecPtr */
    			SpinLockAcquire(&xlogctl->info_lck);
    			xlogctl->replayEndRecPtr = ReadRecPtr;
    			xlogctl->recoveryLastRecPtr = ReadRecPtr;
    			SpinLockRelease(&xlogctl->info_lck);
    
    			InRedo = true;
    
    			ereport(LOG,
    					(errmsg("redo starts at %X/%X",
    							ReadRecPtr.xlogid, ReadRecPtr.xrecoff)));
    
    			/*
    			 * Let postmaster know we've started redo now, so that it can
    			 * launch bgwriter to perform restartpoints.  We don't bother
    			 * during crash recovery as restartpoints can only be performed
    			 * during archive recovery.  And we'd like to keep crash recovery
    			 * simple, to avoid introducing bugs that could you from
    			 * recovering after crash.
    			 *
    			 * After this point, we can no longer assume that we're the only
    			 * process in addition to postmaster!  Also, fsync requests are
    			 * subsequently to be handled by the bgwriter, not locally.
    			 */
    			if (InArchiveRecovery && IsUnderPostmaster)
    			{
    				SetForwardFsyncRequests();
    				SendPostmasterSignal(PMSIGNAL_RECOVERY_STARTED);
    				bgwriterLaunched = true;
    			}
    
    			/*
    			 * main redo apply loop
    			 */
    			do
    			{
    #ifdef WAL_DEBUG
    				if (XLOG_DEBUG ||
    				 (rmid == RM_XACT_ID && trace_recovery_messages <= DEBUG2) ||
    					(rmid != RM_XACT_ID && trace_recovery_messages <= DEBUG3))
    				{
    					StringInfoData buf;
    
    					initStringInfo(&buf);
    					appendStringInfo(&buf, "REDO @ %X/%X; LSN %X/%X: ",
    									 ReadRecPtr.xlogid, ReadRecPtr.xrecoff,
    									 EndRecPtr.xlogid, EndRecPtr.xrecoff);
    					xlog_outrec(&buf, record);
    					appendStringInfo(&buf, " - ");
    					RmgrTable[record->xl_rmid].rm_desc(&buf,
    													   record->xl_info,
    													 XLogRecGetData(record));
    					elog(LOG, "%s", buf.data);
    					pfree(buf.data);
    				}
    #endif
    
    				/* Handle interrupt signals of startup process */
    				HandleStartupProcInterrupts();
    
    				/*
    				 * Have we passed our safe starting point?
    				 */
    				if (!reachedMinRecoveryPoint &&
    					XLByteLE(minRecoveryPoint, EndRecPtr) &&
    					XLogRecPtrIsInvalid(ControlFile->backupStartPoint))
    				{
    					reachedMinRecoveryPoint = true;
    					ereport(LOG,
    						(errmsg("consistent recovery state reached at %X/%X",
    								EndRecPtr.xlogid, EndRecPtr.xrecoff)));
    				}
    
    				/*
    				 * Have we got a valid starting snapshot that will allow
    				 * queries to be run? If so, we can tell postmaster that the
    				 * database is consistent now, enabling connections.
    				 */
    				if (standbyState == STANDBY_SNAPSHOT_READY &&
    					!backendsAllowed &&
    					reachedMinRecoveryPoint &&
    					IsUnderPostmaster)
    				{
    					backendsAllowed = true;
    					SendPostmasterSignal(PMSIGNAL_RECOVERY_CONSISTENT);
    				}
    
    				/*
    				 * Have we reached our recovery target?
    				 */
    				if (recoveryStopsHere(record, &recoveryApply))
    				{
    					reachedStopPoint = true;	/* see below */
    					recoveryContinue = false;
    					if (!recoveryApply)
    						break;
    				}
    
    				/* Setup error traceback support for ereport() */
    				errcontext.callback = rm_redo_error_callback;
    				errcontext.arg = (void *) record;
    				errcontext.previous = error_context_stack;
    				error_context_stack = &errcontext;
    
    				/* nextXid must be beyond record's xid */
    				if (TransactionIdFollowsOrEquals(record->xl_xid,
    												 ShmemVariableCache->nextXid))
    				{
    					ShmemVariableCache->nextXid = record->xl_xid;
    					TransactionIdAdvance(ShmemVariableCache->nextXid);
    				}
    
    				/*
    				 * Update shared replayEndRecPtr before replaying this record,
    				 * so that XLogFlush will update minRecoveryPoint correctly.
    				 */
    				SpinLockAcquire(&xlogctl->info_lck);
    				xlogctl->replayEndRecPtr = EndRecPtr;
    				xlogctl->recoveryLastXTime = recoveryLastXTime;
    				SpinLockRelease(&xlogctl->info_lck);
    
    				/* In Hot Standby mode, keep track of XIDs we've seen */
    				if (InHotStandby && TransactionIdIsValid(record->xl_xid))
    					RecordKnownAssignedTransactionIds(record->xl_xid);
    
    				RmgrTable[record->xl_rmid].rm_redo(EndRecPtr, record);
    
    				/* Pop the error context stack */
    				error_context_stack = errcontext.previous;
    
    				/*
    				 * Update shared recoveryLastRecPtr after this record has been
    				 * replayed.
    				 */
    				SpinLockAcquire(&xlogctl->info_lck);
    				xlogctl->recoveryLastRecPtr = EndRecPtr;
    				SpinLockRelease(&xlogctl->info_lck);
    
    				LastRec = ReadRecPtr;
    
    				record = ReadRecord(NULL, LOG, false);
    			} while (record != NULL && recoveryContinue);
    
    			/*
    			 * end of main redo apply loop
    			 */
    
    			ereport(LOG,
    					(errmsg("redo done at %X/%X",
    							ReadRecPtr.xlogid, ReadRecPtr.xrecoff)));
    			if (recoveryLastXTime)
    				ereport(LOG,
    					 (errmsg("last completed transaction was at log time %s",
    							 timestamptz_to_str(recoveryLastXTime))));
    			InRedo = false;
    		}
    		else
    		{
    			/* there are no WAL records following the checkpoint */
    			ereport(LOG,
    					(errmsg("redo is not required")));
    		}
    	}
    
    	/*
    	 * If we launched a WAL receiver, it should be gone by now. It will trump
    	 * over the startup checkpoint and subsequent records if it's still alive,
    	 * so be extra sure that it's gone.
    	 */
    	if (WalRcvInProgress())
    		elog(PANIC, "wal receiver still active");
    
    	/*
    	 * We are now done reading the xlog from stream. Turn off streaming
    	 * recovery to force fetching the files (which would be required at end of
    	 * recovery, e.g., timeline history file) from archive or pg_xlog.
    	 */
    	StandbyMode = false;
    
    	/*
    	 * Re-fetch the last valid or last applied record, so we can identify the
    	 * exact endpoint of what we consider the valid portion of WAL.
    	 */
    	record = ReadRecord(&LastRec, PANIC, false);
    	EndOfLog = EndRecPtr;
    	XLByteToPrevSeg(EndOfLog, endLogId, endLogSeg);
    
    	/*
    	 * Complain if we did not roll forward far enough to render the backup
    	 * dump consistent.  Note: it is indeed okay to look at the local variable
    	 * minRecoveryPoint here, even though ControlFile->minRecoveryPoint might
    	 * be further ahead --- ControlFile->minRecoveryPoint cannot have been
    	 * advanced beyond the WAL we processed.
    	 */
    	if (InArchiveRecovery &&
    		(XLByteLT(EndOfLog, minRecoveryPoint) ||
    		 !XLogRecPtrIsInvalid(ControlFile->backupStartPoint)))
    	{
    		if (reachedStopPoint)	/* stopped because of stop request */
    			ereport(FATAL,
    					(errmsg("requested recovery stop point is before consistent recovery point")));
    		else	/* ran off end of WAL */
    			ereport(FATAL,
    					(errmsg("WAL ends before consistent recovery point")));
    	}
    
    	/*
    	 * Consider whether we need to assign a new timeline ID.
    	 *
    	 * If we are doing an archive recovery, we always assign a new ID.	This
    	 * handles a couple of issues.	If we stopped short of the end of WAL
    	 * during recovery, then we are clearly generating a new timeline and must
    	 * assign it a unique new ID.  Even if we ran to the end, modifying the
    	 * current last segment is problematic because it may result in trying to
    	 * overwrite an already-archived copy of that segment, and we encourage
    	 * DBAs to make their archive_commands reject that.  We can dodge the
    	 * problem by making the new active segment have a new timeline ID.
    	 *
    	 * In a normal crash recovery, we can just extend the timeline we were in.
    	 */
    	if (InArchiveRecovery)
    	{
    		ThisTimeLineID = findNewestTimeLine(recoveryTargetTLI) + 1;
    		ereport(LOG,
    				(errmsg("selected new timeline ID: %u", ThisTimeLineID)));
    		writeTimeLineHistory(ThisTimeLineID, recoveryTargetTLI,
    							 curFileTLI, endLogId, endLogSeg);
    	}
    
    	/* Save the selected TimeLineID in shared memory, too */
    	XLogCtl->ThisTimeLineID = ThisTimeLineID;
    
    	/*
    	 * We are now done reading the old WAL.  Turn off archive fetching if it
    	 * was active, and make a writable copy of the last WAL segment. (Note
    	 * that we also have a copy of the last block of the old WAL in readBuf;
    	 * we will use that below.)
    	 */
    	if (InArchiveRecovery)
    		exitArchiveRecovery(curFileTLI, endLogId, endLogSeg);
    
    	/*
    	 * Prepare to write WAL starting at EndOfLog position, and init xlog
    	 * buffer cache using the block containing the last record from the
    	 * previous incarnation.
    	 */
    	openLogId = endLogId;
    	openLogSeg = endLogSeg;
    	openLogFile = XLogFileOpen(openLogId, openLogSeg);
    	openLogOff = 0;
    	Insert = &XLogCtl->Insert;
    	Insert->PrevRecord = LastRec;
    	XLogCtl->xlblocks[0].xlogid = openLogId;
    	XLogCtl->xlblocks[0].xrecoff =
    		((EndOfLog.xrecoff - 1) / XLOG_BLCKSZ + 1) * XLOG_BLCKSZ;
    
    	/*
    	 * Tricky point here: readBuf contains the *last* block that the LastRec
    	 * record spans, not the one it starts in.	The last block is indeed the
    	 * one we want to use.
    	 */
    	Assert(readOff == (XLogCtl->xlblocks[0].xrecoff - XLOG_BLCKSZ) % XLogSegSize);
    	memcpy((char *) Insert->currpage, readBuf, XLOG_BLCKSZ);
    	Insert->currpos = (char *) Insert->currpage +
    		(EndOfLog.xrecoff + XLOG_BLCKSZ - XLogCtl->xlblocks[0].xrecoff);
    
    	LogwrtResult.Write = LogwrtResult.Flush = EndOfLog;
    
    	XLogCtl->Write.LogwrtResult = LogwrtResult;
    	Insert->LogwrtResult = LogwrtResult;
    	XLogCtl->LogwrtResult = LogwrtResult;
    
    	XLogCtl->LogwrtRqst.Write = EndOfLog;
    	XLogCtl->LogwrtRqst.Flush = EndOfLog;
    
    	freespace = INSERT_FREESPACE(Insert);
    	if (freespace > 0)
    	{
    		/* Make sure rest of page is zero */
    		MemSet(Insert->currpos, 0, freespace);
    		XLogCtl->Write.curridx = 0;
    	}
    	else
    	{
    		/*
    		 * Whenever Write.LogwrtResult points to exactly the end of a page,
    		 * Write.curridx must point to the *next* page (see XLogWrite()).
    		 *
    		 * Note: it might seem we should do AdvanceXLInsertBuffer() here, but
    		 * this is sufficient.	The first actual attempt to insert a log
    		 * record will advance the insert state.
    		 */
    		XLogCtl->Write.curridx = NextBufIdx(0);
    	}
    
    	/* Pre-scan prepared transactions to find out the range of XIDs present */
    	oldestActiveXID = PrescanPreparedTransactions(NULL, NULL);
    
    	if (InRecovery)
    	{
    		int			rmid;
    
    		/*
    		 * Resource managers might need to write WAL records, eg, to record
    		 * index cleanup actions.  So temporarily enable XLogInsertAllowed in
    		 * this process only.
    		 */
    		LocalSetXLogInsertAllowed();
    
    		/*
    		 * Allow resource managers to do any required cleanup.
    		 */
    		for (rmid = 0; rmid <= RM_MAX_ID; rmid++)
    		{
    			if (RmgrTable[rmid].rm_cleanup != NULL)
    				RmgrTable[rmid].rm_cleanup();
    		}
    
    		/* Disallow XLogInsert again */
    		LocalXLogInsertAllowed = -1;
    
    		/*
    		 * Check to see if the XLOG sequence contained any unresolved
    		 * references to uninitialized pages.
    		 */
    		XLogCheckInvalidPages();
    
    		/*
    		 * Perform a checkpoint to update all our recovery activity to disk.
    		 *
    		 * Note that we write a shutdown checkpoint rather than an on-line
    		 * one. This is not particularly critical, but since we may be
    		 * assigning a new TLI, using a shutdown checkpoint allows us to have
    		 * the rule that TLI only changes in shutdown checkpoints, which
    		 * allows some extra error checking in xlog_redo.
    		 */
    		if (bgwriterLaunched)
    			RequestCheckpoint(CHECKPOINT_END_OF_RECOVERY |
    							  CHECKPOINT_IMMEDIATE |
    							  CHECKPOINT_WAIT);
    		else
    			CreateCheckPoint(CHECKPOINT_END_OF_RECOVERY | CHECKPOINT_IMMEDIATE);
    
    		/*
    		 * And finally, execute the recovery_end_command, if any.
    		 */
    		if (recoveryEndCommand)
    			ExecuteRecoveryCommand(recoveryEndCommand,
    								   "recovery_end_command",
    								   true);
    	}
    
    	/*
    	 * Preallocate additional log files, if wanted.
    	 */
    	PreallocXlogFiles(EndOfLog);
    
    	/*
    	 * Okay, we're officially UP.
    	 */
    	InRecovery = false;
    
    	LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
    	ControlFile->state = DB_IN_PRODUCTION;
    	ControlFile->time = (pg_time_t) time(NULL);
    	UpdateControlFile();
    	LWLockRelease(ControlFileLock);
    
    	/* start the archive_timeout timer running */
    	XLogCtl->Write.lastSegSwitchTime = (pg_time_t) time(NULL);
    
    	/* initialize shared-memory copy of latest checkpoint XID/epoch */
    	XLogCtl->ckptXidEpoch = ControlFile->checkPointCopy.nextXidEpoch;
    	XLogCtl->ckptXid = ControlFile->checkPointCopy.nextXid;
    
    	/* also initialize latestCompletedXid, to nextXid - 1 */
    	ShmemVariableCache->latestCompletedXid = ShmemVariableCache->nextXid;
    	TransactionIdRetreat(ShmemVariableCache->latestCompletedXid);
    
    	/*
    	 * Start up the commit log and related stuff, too. In hot standby mode we
    	 * did this already before WAL replay.
    	 */
    	if (standbyState == STANDBY_DISABLED)
    	{
    		StartupCLOG();
    		StartupSUBTRANS(oldestActiveXID);
    		StartupMultiXact();
    	}
    
    	/* Reload shared-memory state for prepared transactions */
    	RecoverPreparedTransactions();
    
    	/*
    	 * Shutdown the recovery environment. This must occur after
    	 * RecoverPreparedTransactions(), see notes for lock_twophase_recover()
    	 */
    	if (standbyState != STANDBY_DISABLED)
    		ShutdownRecoveryTransactionEnvironment();
    
    	/* Shut down readFile facility, free space */
    	if (readFile >= 0)
    	{
    		close(readFile);
    		readFile = -1;
    	}
    	if (readBuf)
    	{
    		free(readBuf);
    		readBuf = NULL;
    	}
    	if (readRecordBuf)
    	{
    		free(readRecordBuf);
    		readRecordBuf = NULL;
    		readRecordBufSize = 0;
    	}
    
    	/*
    	 * All done.  Allow backends to write WAL.	(Although the bool flag is
    	 * probably atomic in itself, we use the info_lck here to ensure that
    	 * there are no race conditions concerning visibility of other recent
    	 * updates to shared memory.)
    	 */
    	{
    		/* use volatile pointer to prevent code rearrangement */
    		volatile XLogCtlData *xlogctl = XLogCtl;
    
    		SpinLockAcquire(&xlogctl->info_lck);
    		xlogctl->SharedRecoveryInProgress = false;
    		SpinLockRelease(&xlogctl->info_lck);
    	}
    }
    
    /*
     * Is the system still in recovery?
     *
     * Unlike testing InRecovery, this works in any process that's connected to
     * shared memory.
     *
     * As a side-effect, we initialize the local TimeLineID and RedoRecPtr
     * variables the first time we see that recovery is finished.
     */
    bool
    RecoveryInProgress(void)
    {
    	/*
    	 * We check shared state each time only until we leave recovery mode. We
    	 * can't re-enter recovery, so there's no need to keep checking after the
    	 * shared variable has once been seen false.
    	 */
    	if (!LocalRecoveryInProgress)
    		return false;
    	else
    	{
    		/* use volatile pointer to prevent code rearrangement */
    		volatile XLogCtlData *xlogctl = XLogCtl;
    
    		/* spinlock is essential on machines with weak memory ordering! */
    		SpinLockAcquire(&xlogctl->info_lck);
    		LocalRecoveryInProgress = xlogctl->SharedRecoveryInProgress;
    		SpinLockRelease(&xlogctl->info_lck);
    
    		/*
    		 * Initialize TimeLineID and RedoRecPtr when we discover that recovery
    		 * is finished. InitPostgres() relies upon this behaviour to ensure
    		 * that InitXLOGAccess() is called at backend startup.	(If you change
    		 * this, see also LocalSetXLogInsertAllowed.)
    		 */
    		if (!LocalRecoveryInProgress)
    			InitXLOGAccess();
    
    		return LocalRecoveryInProgress;
    	}
    }
    
    /*
     * Is this process allowed to insert new WAL records?
     *
     * Ordinarily this is essentially equivalent to !RecoveryInProgress().
     * But we also have provisions for forcing the result "true" or "false"
     * within specific processes regardless of the global state.
     */
    bool
    XLogInsertAllowed(void)
    {
    	/*
    	 * If value is "unconditionally true" or "unconditionally false", just
    	 * return it.  This provides the normal fast path once recovery is known
    	 * done.
    	 */
    	if (LocalXLogInsertAllowed >= 0)
    		return (bool) LocalXLogInsertAllowed;
    
    	/*
    	 * Else, must check to see if we're still in recovery.
    	 */
    	if (RecoveryInProgress())
    		return false;
    
    	/*
    	 * On exit from recovery, reset to "unconditionally true", since there is
    	 * no need to keep checking.
    	 */
    	LocalXLogInsertAllowed = 1;
    	return true;
    }
    
    /*
     * Make XLogInsertAllowed() return true in the current process only.
     *
     * Note: it is allowed to switch LocalXLogInsertAllowed back to -1 later,
     * and even call LocalSetXLogInsertAllowed() again after that.
     */
    static void
    LocalSetXLogInsertAllowed(void)
    {
    	Assert(LocalXLogInsertAllowed == -1);
    	LocalXLogInsertAllowed = 1;
    
    	/* Initialize as RecoveryInProgress() would do when switching state */
    	InitXLOGAccess();
    }
    
    /*
     * Subroutine to try to fetch and validate a prior checkpoint record.
     *
     * whichChkpt identifies the checkpoint (merely for reporting purposes).
     * 1 for "primary", 2 for "secondary", 0 for "other" (backup_label)
     */
    static XLogRecord *
    ReadCheckpointRecord(XLogRecPtr RecPtr, int whichChkpt)
    {
    	XLogRecord *record;
    
    	if (!XRecOffIsValid(RecPtr.xrecoff))
    	{
    		switch (whichChkpt)
    		{
    			case 1:
    				ereport(LOG,
    				(errmsg("invalid primary checkpoint link in control file")));
    				break;
    			case 2:
    				ereport(LOG,
    						(errmsg("invalid secondary checkpoint link in control file")));
    				break;
    			default:
    				ereport(LOG,
    				   (errmsg("invalid checkpoint link in backup_label file")));
    				break;
    		}
    		return NULL;
    	}
    
    	record = ReadRecord(&RecPtr, LOG, true);
    
    	if (record == NULL)
    	{
    		switch (whichChkpt)
    		{
    			case 1:
    				ereport(LOG,
    						(errmsg("invalid primary checkpoint record")));
    				break;
    			case 2:
    				ereport(LOG,
    						(errmsg("invalid secondary checkpoint record")));
    				break;
    			default:
    				ereport(LOG,
    						(errmsg("invalid checkpoint record")));
    				break;
    		}
    		return NULL;
    	}
    	if (record->xl_rmid != RM_XLOG_ID)
    	{
    		switch (whichChkpt)
    		{
    			case 1:
    				ereport(LOG,
    						(errmsg("invalid resource manager ID in primary checkpoint record")));
    				break;
    			case 2:
    				ereport(LOG,
    						(errmsg("invalid resource manager ID in secondary checkpoint record")));
    				break;
    			default:
    				ereport(LOG,
    				(errmsg("invalid resource manager ID in checkpoint record")));
    				break;
    		}
    		return NULL;
    	}
    	if (record->xl_info != XLOG_CHECKPOINT_SHUTDOWN &&
    		record->xl_info != XLOG_CHECKPOINT_ONLINE)
    	{
    		switch (whichChkpt)
    		{
    			case 1:
    				ereport(LOG,
    				   (errmsg("invalid xl_info in primary checkpoint record")));
    				break;
    			case 2:
    				ereport(LOG,
    				 (errmsg("invalid xl_info in secondary checkpoint record")));
    				break;
    			default:
    				ereport(LOG,
    						(errmsg("invalid xl_info in checkpoint record")));
    				break;
    		}
    		return NULL;
    	}
    	if (record->xl_len != sizeof(CheckPoint) ||
    		record->xl_tot_len != SizeOfXLogRecord + sizeof(CheckPoint))
    	{
    		switch (whichChkpt)
    		{
    			case 1:
    				ereport(LOG,
    					(errmsg("invalid length of primary checkpoint record")));
    				break;
    			case 2:
    				ereport(LOG,
    				  (errmsg("invalid length of secondary checkpoint record")));
    				break;
    			default:
    				ereport(LOG,
    						(errmsg("invalid length of checkpoint record")));
    				break;
    		}
    		return NULL;
    	}
    	return record;
    }
    
    /*
     * This must be called during startup of a backend process, except that
     * it need not be called in a standalone backend (which does StartupXLOG
     * instead).  We need to initialize the local copies of ThisTimeLineID and
     * RedoRecPtr.
     *
     * Note: before Postgres 8.0, we went to some effort to keep the postmaster
     * process's copies of ThisTimeLineID and RedoRecPtr valid too.  This was
     * unnecessary however, since the postmaster itself never touches XLOG anyway.
     */
    void
    InitXLOGAccess(void)
    {
    	/* ThisTimeLineID doesn't change so we need no lock to copy it */
    	ThisTimeLineID = XLogCtl->ThisTimeLineID;
    	Assert(ThisTimeLineID != 0 || IsBootstrapProcessingMode());
    
    	/* Use GetRedoRecPtr to copy the RedoRecPtr safely */
    	(void) GetRedoRecPtr();
    }
    
    /*
     * Once spawned, a backend may update its local RedoRecPtr from
     * XLogCtl->Insert.RedoRecPtr; it must hold the insert lock or info_lck
     * to do so.  This is done in XLogInsert() or GetRedoRecPtr().
     */
    XLogRecPtr
    GetRedoRecPtr(void)
    {
    	/* use volatile pointer to prevent code rearrangement */
    	volatile XLogCtlData *xlogctl = XLogCtl;
    
    	SpinLockAcquire(&xlogctl->info_lck);
    	Assert(XLByteLE(RedoRecPtr, xlogctl->Insert.RedoRecPtr));
    	RedoRecPtr = xlogctl->Insert.RedoRecPtr;
    	SpinLockRelease(&xlogctl->info_lck);
    
    	return RedoRecPtr;
    }
    
    /*
     * GetInsertRecPtr -- Returns the current insert position.
     *
     * NOTE: The value *actually* returned is the position of the last full
     * xlog page. It lags behind the real insert position by at most 1 page.
     * For that, we don't need to acquire WALInsertLock which can be quite
     * heavily contended, and an approximation is enough for the current
     * usage of this function.
     */
    XLogRecPtr
    GetInsertRecPtr(void)
    {
    	/* use volatile pointer to prevent code rearrangement */
    	volatile XLogCtlData *xlogctl = XLogCtl;
    	XLogRecPtr	recptr;
    
    	SpinLockAcquire(&xlogctl->info_lck);
    	recptr = xlogctl->LogwrtRqst.Write;
    	SpinLockRelease(&xlogctl->info_lck);
    
    	return recptr;
    }
    
    /*
     * GetWriteRecPtr -- Returns the current write position.
     */
    XLogRecPtr
    GetWriteRecPtr(void)
    {
    	/* use volatile pointer to prevent code rearrangement */
    	volatile XLogCtlData *xlogctl = XLogCtl;
    	XLogRecPtr	recptr;
    
    	SpinLockAcquire(&xlogctl->info_lck);
    	recptr = xlogctl->LogwrtResult.Write;
    	SpinLockRelease(&xlogctl->info_lck);
    
    	return recptr;
    }
    
    /*
     * Get the time of the last xlog segment switch
     */
    pg_time_t
    GetLastSegSwitchTime(void)
    {
    	pg_time_t	result;
    
    	/* Need WALWriteLock, but shared lock is sufficient */
    	LWLockAcquire(WALWriteLock, LW_SHARED);
    	result = XLogCtl->Write.lastSegSwitchTime;
    	LWLockRelease(WALWriteLock);
    
    	return result;
    }
    
    /*
     * GetNextXidAndEpoch - get the current nextXid value and associated epoch
     *
     * This is exported for use by code that would like to have 64-bit XIDs.
     * We don't really support such things, but all XIDs within the system
     * can be presumed "close to" the result, and thus the epoch associated
     * with them can be determined.
     */
    void
    GetNextXidAndEpoch(TransactionId *xid, uint32 *epoch)
    {
    	uint32		ckptXidEpoch;
    	TransactionId ckptXid;
    	TransactionId nextXid;
    
    	/* Must read checkpoint info first, else have race condition */
    	{
    		/* use volatile pointer to prevent code rearrangement */
    		volatile XLogCtlData *xlogctl = XLogCtl;
    
    		SpinLockAcquire(&xlogctl->info_lck);
    		ckptXidEpoch = xlogctl->ckptXidEpoch;
    		ckptXid = xlogctl->ckptXid;
    		SpinLockRelease(&xlogctl->info_lck);
    	}
    
    	/* Now fetch current nextXid */
    	nextXid = ReadNewTransactionId();
    
    	/*
    	 * nextXid is certainly logically later than ckptXid.  So if it's
    	 * numerically less, it must have wrapped into the next epoch.
    	 */
    	if (nextXid < ckptXid)
    		ckptXidEpoch++;
    
    	*xid = nextXid;
    	*epoch = ckptXidEpoch;
    }
    
    /*
     * GetRecoveryTargetTLI - get the recovery target timeline ID
     */
    TimeLineID
    GetRecoveryTargetTLI(void)
    {
    	/* RecoveryTargetTLI doesn't change so we need no lock to copy it */
    	return XLogCtl->RecoveryTargetTLI;
    }
    
    /*
     * This must be called ONCE during postmaster or standalone-backend shutdown
     */
    void
    ShutdownXLOG(int code, Datum arg)
    {
    	ereport(LOG,
    			(errmsg("shutting down")));
    
    	if (RecoveryInProgress())
    		CreateRestartPoint(CHECKPOINT_IS_SHUTDOWN | CHECKPOINT_IMMEDIATE);
    	else
    	{
    		/*
    		 * If archiving is enabled, rotate the last XLOG file so that all the
    		 * remaining records are archived (postmaster wakes up the archiver
    		 * process one more time at the end of shutdown). The checkpoint
    		 * record will go to the next XLOG file and won't be archived (yet).
    		 */
    		if (XLogArchivingActive() && XLogArchiveCommandSet())
    			RequestXLogSwitch();
    
    		CreateCheckPoint(CHECKPOINT_IS_SHUTDOWN | CHECKPOINT_IMMEDIATE);
    	}
    	ShutdownCLOG();
    	ShutdownSUBTRANS();
    	ShutdownMultiXact();
    
    	ereport(LOG,
    			(errmsg("database system is shut down")));
    }
    
    /*
     * Log start of a checkpoint.
     */
    static void
    LogCheckpointStart(int flags, bool restartpoint)
    {
    	const char *msg;
    
    	/*
    	 * XXX: This is hopelessly untranslatable. We could call gettext_noop for
    	 * the main message, but what about all the flags?
    	 */
    	if (restartpoint)
    		msg = "restartpoint starting:%s%s%s%s%s%s%s";
    	else
    		msg = "checkpoint starting:%s%s%s%s%s%s%s";
    
    	elog(LOG, msg,
    		 (flags & CHECKPOINT_IS_SHUTDOWN) ? " shutdown" : "",
    		 (flags & CHECKPOINT_END_OF_RECOVERY) ? " end-of-recovery" : "",
    		 (flags & CHECKPOINT_IMMEDIATE) ? " immediate" : "",
    		 (flags & CHECKPOINT_FORCE) ? " force" : "",
    		 (flags & CHECKPOINT_WAIT) ? " wait" : "",
    		 (flags & CHECKPOINT_CAUSE_XLOG) ? " xlog" : "",
    		 (flags & CHECKPOINT_CAUSE_TIME) ? " time" : "");
    }
    
    /*
     * Log end of a checkpoint.
     */
    static void
    LogCheckpointEnd(bool restartpoint)
    {
    	long		write_secs,
    				sync_secs,
    				total_secs;
    	int			write_usecs,
    				sync_usecs,
    				total_usecs;
    
    	CheckpointStats.ckpt_end_t = GetCurrentTimestamp();
    
    	TimestampDifference(CheckpointStats.ckpt_start_t,
    						CheckpointStats.ckpt_end_t,
    						&total_secs, &total_usecs);
    
    	TimestampDifference(CheckpointStats.ckpt_write_t,
    						CheckpointStats.ckpt_sync_t,
    						&write_secs, &write_usecs);
    
    	TimestampDifference(CheckpointStats.ckpt_sync_t,
    						CheckpointStats.ckpt_sync_end_t,
    						&sync_secs, &sync_usecs);
    
    	if (restartpoint)
    		elog(LOG, "restartpoint complete: wrote %d buffers (%.1f%%); "
    			 "write=%ld.%03d s, sync=%ld.%03d s, total=%ld.%03d s",
    			 CheckpointStats.ckpt_bufs_written,
    			 (double) CheckpointStats.ckpt_bufs_written * 100 / NBuffers,
    			 write_secs, write_usecs / 1000,
    			 sync_secs, sync_usecs / 1000,
    			 total_secs, total_usecs / 1000);
    	else
    		elog(LOG, "checkpoint complete: wrote %d buffers (%.1f%%); "
    			 "%d transaction log file(s) added, %d removed, %d recycled; "
    			 "write=%ld.%03d s, sync=%ld.%03d s, total=%ld.%03d s",
    			 CheckpointStats.ckpt_bufs_written,
    			 (double) CheckpointStats.ckpt_bufs_written * 100 / NBuffers,
    			 CheckpointStats.ckpt_segs_added,
    			 CheckpointStats.ckpt_segs_removed,
    			 CheckpointStats.ckpt_segs_recycled,
    			 write_secs, write_usecs / 1000,
    			 sync_secs, sync_usecs / 1000,
    			 total_secs, total_usecs / 1000);
    }
    
    /*
     * Perform a checkpoint --- either during shutdown, or on-the-fly
     *
     * flags is a bitwise OR of the following:
     *	CHECKPOINT_IS_SHUTDOWN: checkpoint is for database shutdown.
     *	CHECKPOINT_END_OF_RECOVERY: checkpoint is for end of WAL recovery.
     *	CHECKPOINT_IMMEDIATE: finish the checkpoint ASAP,
     *		ignoring checkpoint_completion_target parameter.
     *	CHECKPOINT_FORCE: force a checkpoint even if no XLOG activity has occured
     *		since the last one (implied by CHECKPOINT_IS_SHUTDOWN or
     *		CHECKPOINT_END_OF_RECOVERY).
     *
     * Note: flags contains other bits, of interest here only for logging purposes.
     * In particular note that this routine is synchronous and does not pay
     * attention to CHECKPOINT_WAIT.
     */
    void
    CreateCheckPoint(int flags)
    {
    	bool		shutdown;
    	CheckPoint	checkPoint;
    	XLogRecPtr	recptr;
    	XLogCtlInsert *Insert = &XLogCtl->Insert;
    	XLogRecData rdata;
    	uint32		freespace;
    	uint32		_logId;
    	uint32		_logSeg;
    	TransactionId *inCommitXids;
    	int			nInCommit;
    
    	/*
    	 * An end-of-recovery checkpoint is really a shutdown checkpoint, just
    	 * issued at a different time.
    	 */
    	if (flags & (CHECKPOINT_IS_SHUTDOWN | CHECKPOINT_END_OF_RECOVERY))
    		shutdown = true;
    	else
    		shutdown = false;
    
    	/* sanity check */
    	if (RecoveryInProgress() && (flags & CHECKPOINT_END_OF_RECOVERY) == 0)
    		elog(ERROR, "can't create a checkpoint during recovery");
    
    	/*
    	 * Acquire CheckpointLock to ensure only one checkpoint happens at a time.
    	 * (This is just pro forma, since in the present system structure there is
    	 * only one process that is allowed to issue checkpoints at any given
    	 * time.)
    	 */
    	LWLockAcquire(CheckpointLock, LW_EXCLUSIVE);
    
    	/*
    	 * Prepare to accumulate statistics.
    	 *
    	 * Note: because it is possible for log_checkpoints to change while a
    	 * checkpoint proceeds, we always accumulate stats, even if
    	 * log_checkpoints is currently off.
    	 */
    	MemSet(&CheckpointStats, 0, sizeof(CheckpointStats));
    	CheckpointStats.ckpt_start_t = GetCurrentTimestamp();
    
    	/*
    	 * Use a critical section to force system panic if we have trouble.
    	 */
    	START_CRIT_SECTION();
    
    	if (shutdown)
    	{
    		LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
    		ControlFile->state = DB_SHUTDOWNING;
    		ControlFile->time = (pg_time_t) time(NULL);
    		UpdateControlFile();
    		LWLockRelease(ControlFileLock);
    	}
    
    	/*
    	 * Let smgr prepare for checkpoint; this has to happen before we determine
    	 * the REDO pointer.  Note that smgr must not do anything that'd have to
    	 * be undone if we decide no checkpoint is needed.
    	 */
    	smgrpreckpt();
    
    	/* Begin filling in the checkpoint WAL record */
    	MemSet(&checkPoint, 0, sizeof(checkPoint));
    	checkPoint.time = (pg_time_t) time(NULL);
    
    	/* Set important parameter values for use when replaying WAL */
    	checkPoint.MaxConnections = MaxConnections;
    	checkPoint.max_prepared_xacts = max_prepared_xacts;
    	checkPoint.max_locks_per_xact = max_locks_per_xact;
    	checkPoint.XLogStandbyInfoMode = XLogStandbyInfoActive();
    
    	/*
    	 * We must hold WALInsertLock while examining insert state to determine
    	 * the checkpoint REDO pointer.
    	 */
    	LWLockAcquire(WALInsertLock, LW_EXCLUSIVE);
    
    	/*
    	 * If this isn't a shutdown or forced checkpoint, and we have not inserted
    	 * any XLOG records since the start of the last checkpoint, skip the
    	 * checkpoint.	The idea here is to avoid inserting duplicate checkpoints
    	 * when the system is idle. That wastes log space, and more importantly it
    	 * exposes us to possible loss of both current and previous checkpoint
    	 * records if the machine crashes just as we're writing the update.
    	 * (Perhaps it'd make even more sense to checkpoint only when the previous
    	 * checkpoint record is in a different xlog page?)
    	 *
    	 * We have to make two tests to determine that nothing has happened since
    	 * the start of the last checkpoint: current insertion point must match
    	 * the end of the last checkpoint record, and its redo pointer must point
    	 * to itself.
    	 */
    	if ((flags & (CHECKPOINT_IS_SHUTDOWN | CHECKPOINT_END_OF_RECOVERY |
    				  CHECKPOINT_FORCE)) == 0)
    	{
    		XLogRecPtr	curInsert;
    
    		INSERT_RECPTR(curInsert, Insert, Insert->curridx);
    		if (curInsert.xlogid == ControlFile->checkPoint.xlogid &&
    			curInsert.xrecoff == ControlFile->checkPoint.xrecoff +
    			MAXALIGN(SizeOfXLogRecord + sizeof(CheckPoint)) &&
    			ControlFile->checkPoint.xlogid ==
    			ControlFile->checkPointCopy.redo.xlogid &&
    			ControlFile->checkPoint.xrecoff ==
    			ControlFile->checkPointCopy.redo.xrecoff)
    		{
    			LWLockRelease(WALInsertLock);
    			LWLockRelease(CheckpointLock);
    			END_CRIT_SECTION();
    			return;
    		}
    	}
    
    	/*
    	 * An end-of-recovery checkpoint is created before anyone is allowed to
    	 * write WAL. To allow us to write the checkpoint record, temporarily
    	 * enable XLogInsertAllowed.  (This also ensures ThisTimeLineID is
    	 * initialized, which we need here and in AdvanceXLInsertBuffer.)
    	 */
    	if (flags & CHECKPOINT_END_OF_RECOVERY)
    		LocalSetXLogInsertAllowed();
    
    	checkPoint.ThisTimeLineID = ThisTimeLineID;
    
    	/*
    	 * Compute new REDO record ptr = location of next XLOG record.
    	 *
    	 * NB: this is NOT necessarily where the checkpoint record itself will be,
    	 * since other backends may insert more XLOG records while we're off doing
    	 * the buffer flush work.  Those XLOG records are logically after the
    	 * checkpoint, even though physically before it.  Got that?
    	 */
    	freespace = INSERT_FREESPACE(Insert);
    	if (freespace < SizeOfXLogRecord)
    	{
    		(void) AdvanceXLInsertBuffer(false);
    		/* OK to ignore update return flag, since we will do flush anyway */
    		freespace = INSERT_FREESPACE(Insert);
    	}
    	INSERT_RECPTR(checkPoint.redo, Insert, Insert->curridx);
    
    	/*
    	 * Here we update the shared RedoRecPtr for future XLogInsert calls; this
    	 * must be done while holding the insert lock AND the info_lck.
    	 *
    	 * Note: if we fail to complete the checkpoint, RedoRecPtr will be left
    	 * pointing past where it really needs to point.  This is okay; the only
    	 * consequence is that XLogInsert might back up whole buffers that it
    	 * didn't really need to.  We can't postpone advancing RedoRecPtr because
    	 * XLogInserts that happen while we are dumping buffers must assume that
    	 * their buffer changes are not included in the checkpoint.
    	 */
    	{
    		/* use volatile pointer to prevent code rearrangement */
    		volatile XLogCtlData *xlogctl = XLogCtl;
    
    		SpinLockAcquire(&xlogctl->info_lck);
    		RedoRecPtr = xlogctl->Insert.RedoRecPtr = checkPoint.redo;
    		SpinLockRelease(&xlogctl->info_lck);
    	}
    
    	/*
    	 * Now we can release WAL insert lock, allowing other xacts to proceed
    	 * while we are flushing disk buffers.
    	 */
    	LWLockRelease(WALInsertLock);
    
    	/*
    	 * If enabled, log checkpoint start.  We postpone this until now so as not
    	 * to log anything if we decided to skip the checkpoint.
    	 */
    	if (log_checkpoints)
    		LogCheckpointStart(flags, false);
    
    	TRACE_POSTGRESQL_CHECKPOINT_START(flags);
    
    	/*
    	 * Before flushing data, we must wait for any transactions that are
    	 * currently in their commit critical sections.  If an xact inserted its
    	 * commit record into XLOG just before the REDO point, then a crash
    	 * restart from the REDO point would not replay that record, which means
    	 * that our flushing had better include the xact's update of pg_clog.  So
    	 * we wait till he's out of his commit critical section before proceeding.
    	 * See notes in RecordTransactionCommit().
    	 *
    	 * Because we've already released WALInsertLock, this test is a bit fuzzy:
    	 * it is possible that we will wait for xacts we didn't really need to
    	 * wait for.  But the delay should be short and it seems better to make
    	 * checkpoint take a bit longer than to hold locks longer than necessary.
    	 * (In fact, the whole reason we have this issue is that xact.c does
    	 * commit record XLOG insertion and clog update as two separate steps
    	 * protected by different locks, but again that seems best on grounds of
    	 * minimizing lock contention.)
    	 *
    	 * A transaction that has not yet set inCommit when we look cannot be at
    	 * risk, since he's not inserted his commit record yet; and one that's
    	 * already cleared it is not at risk either, since he's done fixing clog
    	 * and we will correctly flush the update below.  So we cannot miss any
    	 * xacts we need to wait for.
    	 */
    	nInCommit = GetTransactionsInCommit(&inCommitXids);
    	if (nInCommit > 0)
    	{
    		do
    		{
    			pg_usleep(10000L);	/* wait for 10 msec */
    		} while (HaveTransactionsInCommit(inCommitXids, nInCommit));
    	}
    	pfree(inCommitXids);
    
    	/*
    	 * Get the other info we need for the checkpoint record.
    	 */
    	LWLockAcquire(XidGenLock, LW_SHARED);
    	checkPoint.nextXid = ShmemVariableCache->nextXid;
    	checkPoint.oldestXid = ShmemVariableCache->oldestXid;
    	checkPoint.oldestXidDB = ShmemVariableCache->oldestXidDB;
    	LWLockRelease(XidGenLock);
    
    	/* Increase XID epoch if we've wrapped around since last checkpoint */
    	checkPoint.nextXidEpoch = ControlFile->checkPointCopy.nextXidEpoch;
    	if (checkPoint.nextXid < ControlFile->checkPointCopy.nextXid)
    		checkPoint.nextXidEpoch++;
    
    	LWLockAcquire(OidGenLock, LW_SHARED);
    	checkPoint.nextOid = ShmemVariableCache->nextOid;
    	if (!shutdown)
    		checkPoint.nextOid += ShmemVariableCache->oidCount;
    	LWLockRelease(OidGenLock);
    
    	MultiXactGetCheckptMulti(shutdown,
    							 &checkPoint.nextMulti,
    							 &checkPoint.nextMultiOffset);
    
    	/*
    	 * Having constructed the checkpoint record, ensure all shmem disk buffers
    	 * and commit-log buffers are flushed to disk.
    	 *
    	 * This I/O could fail for various reasons.  If so, we will fail to
    	 * complete the checkpoint, but there is no reason to force a system
    	 * panic. Accordingly, exit critical section while doing it.
    	 */
    	END_CRIT_SECTION();
    
    	CheckPointGuts(checkPoint.redo, flags);
    
    	/*
    	 * Take a snapshot of running transactions and write this to WAL. This
    	 * allows us to reconstruct the state of running transactions during
    	 * archive recovery, if required. Skip, if this info disabled.
    	 *
    	 * If we are shutting down, or Startup process is completing crash
    	 * recovery we don't need to write running xact data.
    	 *
    	 * Update checkPoint.nextXid since we have a later value
    	 */
    	if (!shutdown && XLogStandbyInfoActive())
    		LogStandbySnapshot(&checkPoint.oldestActiveXid, &checkPoint.nextXid);
    	else
    		checkPoint.oldestActiveXid = InvalidTransactionId;
    
    	START_CRIT_SECTION();
    
    	/*
    	 * Now insert the checkpoint record into XLOG.
    	 */
    	rdata.data = (char *) (&checkPoint);
    	rdata.len = sizeof(checkPoint);
    	rdata.buffer = InvalidBuffer;
    	rdata.next = NULL;
    
    	recptr = XLogInsert(RM_XLOG_ID,
    						shutdown ? XLOG_CHECKPOINT_SHUTDOWN :
    						XLOG_CHECKPOINT_ONLINE,
    						&rdata);
    
    	XLogFlush(recptr);
    
    	/*
    	 * We mustn't write any new WAL after a shutdown checkpoint, or it will be
    	 * overwritten at next startup.  No-one should even try, this just allows
    	 * sanity-checking.  In the case of an end-of-recovery checkpoint, we want
    	 * to just temporarily disable writing until the system has exited
    	 * recovery.
    	 */
    	if (shutdown)
    	{
    		if (flags & CHECKPOINT_END_OF_RECOVERY)
    			LocalXLogInsertAllowed = -1;		/* return to "check" state */
    		else
    			LocalXLogInsertAllowed = 0; /* never again write WAL */
    	}
    
    	/*
    	 * We now have ProcLastRecPtr = start of actual checkpoint record, recptr
    	 * = end of actual checkpoint record.
    	 */
    	if (shutdown && !XLByteEQ(checkPoint.redo, ProcLastRecPtr))
    		ereport(PANIC,
    				(errmsg("concurrent transaction log activity while database system is shutting down")));
    
    	/*
    	 * Select point at which we can truncate the log, which we base on the
    	 * prior checkpoint's earliest info.
    	 */
    	XLByteToSeg(ControlFile->checkPointCopy.redo, _logId, _logSeg);
    
    	/*
    	 * Update the control file.
    	 */
    	LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
    	if (shutdown)
    		ControlFile->state = DB_SHUTDOWNED;
    	ControlFile->prevCheckPoint = ControlFile->checkPoint;
    	ControlFile->checkPoint = ProcLastRecPtr;
    	ControlFile->checkPointCopy = checkPoint;
    	ControlFile->time = (pg_time_t) time(NULL);
    	/* crash recovery should always recover to the end of WAL */
    	MemSet(&ControlFile->minRecoveryPoint, 0, sizeof(XLogRecPtr));
    	UpdateControlFile();
    	LWLockRelease(ControlFileLock);
    
    	/* Update shared-memory copy of checkpoint XID/epoch */
    	{
    		/* use volatile pointer to prevent code rearrangement */
    		volatile XLogCtlData *xlogctl = XLogCtl;
    
    		SpinLockAcquire(&xlogctl->info_lck);
    		xlogctl->ckptXidEpoch = checkPoint.nextXidEpoch;
    		xlogctl->ckptXid = checkPoint.nextXid;
    		SpinLockRelease(&xlogctl->info_lck);
    	}
    
    	/*
    	 * We are now done with critical updates; no need for system panic if we
    	 * have trouble while fooling with old log segments.
    	 */
    	END_CRIT_SECTION();
    
    	/*
    	 * Let smgr do post-checkpoint cleanup (eg, deleting old files).
    	 */
    	smgrpostckpt();
    
    	/*
    	 * If there's connected standby servers doing XLOG streaming, don't delete
    	 * XLOG files that have not been streamed to all of them yet. This does
    	 * nothing to prevent them from being deleted when the standby is
    	 * disconnected (e.g because of network problems), but at least it avoids
    	 * an open replication connection from failing because of that.
    	 */
    	if ((_logId || _logSeg) && MaxWalSenders > 0)
    	{
    		XLogRecPtr	oldest;
    		uint32		log;
    		uint32		seg;
    
    		oldest = GetOldestWALSendPointer();
    		if (oldest.xlogid != 0 || oldest.xrecoff != 0)
    		{
    			XLByteToSeg(oldest, log, seg);
    			if (log < _logId || (log == _logId && seg < _logSeg))
    			{
    				_logId = log;
    				_logSeg = seg;
    			}
    		}
    	}
    
    	/*
    	 * Delete old log files (those no longer needed even for previous
    	 * checkpoint or the standbys in XLOG streaming).
    	 */
    	if (_logId || _logSeg)
    	{
    		PrevLogSeg(_logId, _logSeg);
    		RemoveOldXlogFiles(_logId, _logSeg, recptr);
    	}
    
    	/*
    	 * Make more log segments if needed.  (Do this after recycling old log
    	 * segments, since that may supply some of the needed files.)
    	 */
    	if (!shutdown)
    		PreallocXlogFiles(recptr);
    
    	/*
    	 * Truncate pg_subtrans if possible.  We can throw away all data before
    	 * the oldest XMIN of any running transaction.	No future transaction will
    	 * attempt to reference any pg_subtrans entry older than that (see Asserts
    	 * in subtrans.c).	During recovery, though, we mustn't do this because
    	 * StartupSUBTRANS hasn't been called yet.
    	 */
    	if (!RecoveryInProgress())
    		TruncateSUBTRANS(GetOldestXmin(true, false));
    
    	/* All real work is done, but log before releasing lock. */
    	if (log_checkpoints)
    		LogCheckpointEnd(false);
    
    	TRACE_POSTGRESQL_CHECKPOINT_DONE(CheckpointStats.ckpt_bufs_written,
    									 NBuffers,
    									 CheckpointStats.ckpt_segs_added,
    									 CheckpointStats.ckpt_segs_removed,
    									 CheckpointStats.ckpt_segs_recycled);
    
    	LWLockRelease(CheckpointLock);
    }
    
    /*
     * Flush all data in shared memory to disk, and fsync
     *
     * This is the common code shared between regular checkpoints and
     * recovery restartpoints.
     */
    static void
    CheckPointGuts(XLogRecPtr checkPointRedo, int flags)
    {
    	CheckPointCLOG();
    	CheckPointSUBTRANS();
    	CheckPointMultiXact();
    	CheckPointRelationMap();
    	CheckPointBuffers(flags);	/* performs all required fsyncs */
    	/* We deliberately delay 2PC checkpointing as long as possible */
    	CheckPointTwoPhase(checkPointRedo);
    }
    
    /*
     * Save a checkpoint for recovery restart if appropriate
     *
     * This function is called each time a checkpoint record is read from XLOG.
     * It must determine whether the checkpoint represents a safe restartpoint or
     * not.  If so, the checkpoint record is stashed in shared memory so that
     * CreateRestartPoint can consult it.  (Note that the latter function is
     * executed by the bgwriter, while this one will be executed by the startup
     * process.)
     */
    static void
    RecoveryRestartPoint(const CheckPoint *checkPoint)
    {
    	int			rmid;
    
    	/* use volatile pointer to prevent code rearrangement */
    	volatile XLogCtlData *xlogctl = XLogCtl;
    
    	/*
    	 * Is it safe to checkpoint?  We must ask each of the resource managers
    	 * whether they have any partial state information that might prevent a
    	 * correct restart from this point.  If so, we skip this opportunity, but
    	 * return at the next checkpoint record for another try.
    	 */
    	for (rmid = 0; rmid <= RM_MAX_ID; rmid++)
    	{
    		if (RmgrTable[rmid].rm_safe_restartpoint != NULL)
    			if (!(RmgrTable[rmid].rm_safe_restartpoint()))
    			{
    				elog(trace_recovery(DEBUG2), "RM %d not safe to record restart point at %X/%X",
    					 rmid,
    					 checkPoint->redo.xlogid,
    					 checkPoint->redo.xrecoff);
    				return;
    			}
    	}
    
    	/*
    	 * Copy the checkpoint record to shared memory, so that bgwriter can use
    	 * it the next time it wants to perform a restartpoint.
    	 */
    	SpinLockAcquire(&xlogctl->info_lck);
    	XLogCtl->lastCheckPointRecPtr = ReadRecPtr;
    	memcpy(&XLogCtl->lastCheckPoint, checkPoint, sizeof(CheckPoint));
    	SpinLockRelease(&xlogctl->info_lck);
    }
    
    /*
     * Establish a restartpoint if possible.
     *
     * This is similar to CreateCheckPoint, but is used during WAL recovery
     * to establish a point from which recovery can roll forward without
     * replaying the entire recovery log.
     *
     * Returns true if a new restartpoint was established. We can only establish
     * a restartpoint if we have replayed a safe checkpoint record since last
     * restartpoint.
     */
    bool
    CreateRestartPoint(int flags)
    {
    	XLogRecPtr	lastCheckPointRecPtr;
    	CheckPoint	lastCheckPoint;
    	uint32		_logId;
    	uint32		_logSeg;
    
    	/* use volatile pointer to prevent code rearrangement */
    	volatile XLogCtlData *xlogctl = XLogCtl;
    
    	/*
    	 * Acquire CheckpointLock to ensure only one restartpoint or checkpoint
    	 * happens at a time.
    	 */
    	LWLockAcquire(CheckpointLock, LW_EXCLUSIVE);
    
    	/* Get a local copy of the last safe checkpoint record. */
    	SpinLockAcquire(&xlogctl->info_lck);
    	lastCheckPointRecPtr = xlogctl->lastCheckPointRecPtr;
    	memcpy(&lastCheckPoint, &XLogCtl->lastCheckPoint, sizeof(CheckPoint));
    	SpinLockRelease(&xlogctl->info_lck);
    
    	/*
    	 * Check that we're still in recovery mode. It's ok if we exit recovery
    	 * mode after this check, the restart point is valid anyway.
    	 */
    	if (!RecoveryInProgress())
    	{
    		ereport(DEBUG2,
    			  (errmsg("skipping restartpoint, recovery has already ended")));
    		LWLockRelease(CheckpointLock);
    		return false;
    	}
    
    	/*
    	 * If the last checkpoint record we've replayed is already our last
    	 * restartpoint, we can't perform a new restart point. We still update
    	 * minRecoveryPoint in that case, so that if this is a shutdown restart
    	 * point, we won't start up earlier than before. That's not strictly
    	 * necessary, but when we get hot standby capability, it would be rather
    	 * weird if the database opened up for read-only connections at a
    	 * point-in-time before the last shutdown. Such time travel is still
    	 * possible in case of immediate shutdown, though.
    	 *
    	 * We don't explicitly advance minRecoveryPoint when we do create a
    	 * restartpoint. It's assumed that flushing the buffers will do that as a
    	 * side-effect.
    	 */
    	if (XLogRecPtrIsInvalid(lastCheckPointRecPtr) ||
    		XLByteLE(lastCheckPoint.redo, ControlFile->checkPointCopy.redo))
    	{
    		XLogRecPtr	InvalidXLogRecPtr = {0, 0};
    
    		ereport(DEBUG2,
    				(errmsg("skipping restartpoint, already performed at %X/%X",
    				  lastCheckPoint.redo.xlogid, lastCheckPoint.redo.xrecoff)));
    
    		UpdateMinRecoveryPoint(InvalidXLogRecPtr, true);
    		LWLockRelease(CheckpointLock);
    		return false;
    	}
    
    	if (log_checkpoints)
    	{
    		/*
    		 * Prepare to accumulate statistics.
    		 */
    		MemSet(&CheckpointStats, 0, sizeof(CheckpointStats));
    		CheckpointStats.ckpt_start_t = GetCurrentTimestamp();
    
    		LogCheckpointStart(flags, true);
    	}
    
    	CheckPointGuts(lastCheckPoint.redo, flags);
    
    	/*
    	 * Select point at which we can truncate the xlog, which we base on the
    	 * prior checkpoint's earliest info.
    	 */
    	XLByteToSeg(ControlFile->checkPointCopy.redo, _logId, _logSeg);
    
    	/*
    	 * Update pg_control, using current time.  Check that it still shows
    	 * IN_ARCHIVE_RECOVERY state and an older checkpoint, else do nothing;
    	 * this is a quick hack to make sure nothing really bad happens if somehow
    	 * we get here after the end-of-recovery checkpoint.
    	 */
    	LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
    	if (ControlFile->state == DB_IN_ARCHIVE_RECOVERY &&
    		XLByteLT(ControlFile->checkPointCopy.redo, lastCheckPoint.redo))
    	{
    		ControlFile->prevCheckPoint = ControlFile->checkPoint;
    		ControlFile->checkPoint = lastCheckPointRecPtr;
    		ControlFile->checkPointCopy = lastCheckPoint;
    		ControlFile->time = (pg_time_t) time(NULL);
    		UpdateControlFile();
    	}
    	LWLockRelease(ControlFileLock);
    
    	/*
    	 * Delete old log files (those no longer needed even for previous
    	 * checkpoint/restartpoint) to prevent the disk holding the xlog from
    	 * growing full. We don't need do this during normal recovery, but during
    	 * streaming recovery we have to or the disk will eventually fill up from
    	 * old log files streamed from master.
    	 */
    	if (WalRcvInProgress() && (_logId || _logSeg))
    	{
    		XLogRecPtr	endptr;
    
    		/* Get the current (or recent) end of xlog */
    		endptr = GetWalRcvWriteRecPtr();
    
    		PrevLogSeg(_logId, _logSeg);
    		RemoveOldXlogFiles(_logId, _logSeg, endptr);
    
    		/*
    		 * Make more log segments if needed.  (Do this after recycling old log
    		 * segments, since that may supply some of the needed files.)
    		 */
    		PreallocXlogFiles(endptr);
    	}
    
    	/*
    	 * Currently, there is no need to truncate pg_subtrans during recovery. If
    	 * we did do that, we will need to have called StartupSUBTRANS() already
    	 * and then TruncateSUBTRANS() would go here.
    	 */
    
    	/* All real work is done, but log before releasing lock. */
    	if (log_checkpoints)
    		LogCheckpointEnd(true);
    
    	ereport((log_checkpoints ? LOG : DEBUG2),
    	 (errmsg("recovery restart point at %X/%X with latest known log time %s",
    			 lastCheckPoint.redo.xlogid, lastCheckPoint.redo.xrecoff,
    			 timestamptz_to_str(GetLatestXLogTime()))));
    
    	LWLockRelease(CheckpointLock);
    
    	/*
    	 * Finally, execute restartpoint_command, if any.
    	 */
    	if (XLogCtl->restartPointCommand[0])
    		ExecuteRecoveryCommand(XLogCtl->restartPointCommand,
    							   "restartpoint_command",
    							   false);
    
    	return true;
    }
    
    /*
     * Write a NEXTOID log record
     */
    void
    XLogPutNextOid(Oid nextOid)
    {
    	XLogRecData rdata;
    
    	rdata.data = (char *) (&nextOid);
    	rdata.len = sizeof(Oid);
    	rdata.buffer = InvalidBuffer;
    	rdata.next = NULL;
    	(void) XLogInsert(RM_XLOG_ID, XLOG_NEXTOID, &rdata);
    
    	/*
    	 * We need not flush the NEXTOID record immediately, because any of the
    	 * just-allocated OIDs could only reach disk as part of a tuple insert or
    	 * update that would have its own XLOG record that must follow the NEXTOID
    	 * record.	Therefore, the standard buffer LSN interlock applied to those
    	 * records will ensure no such OID reaches disk before the NEXTOID record
    	 * does.
    	 *
    	 * Note, however, that the above statement only covers state "within" the
    	 * database.  When we use a generated OID as a file or directory name, we
    	 * are in a sense violating the basic WAL rule, because that filesystem
    	 * change may reach disk before the NEXTOID WAL record does.  The impact
    	 * of this is that if a database crash occurs immediately afterward, we
    	 * might after restart re-generate the same OID and find that it conflicts
    	 * with the leftover file or directory.  But since for safety's sake we
    	 * always loop until finding a nonconflicting filename, this poses no real
    	 * problem in practice. See pgsql-hackers discussion 27-Sep-2006.
    	 */
    }
    
    /*
     * Write an XLOG SWITCH record.
     *
     * Here we just blindly issue an XLogInsert request for the record.
     * All the magic happens inside XLogInsert.
     *
     * The return value is either the end+1 address of the switch record,
     * or the end+1 address of the prior segment if we did not need to
     * write a switch record because we are already at segment start.
     */
    XLogRecPtr
    RequestXLogSwitch(void)
    {
    	XLogRecPtr	RecPtr;
    	XLogRecData rdata;
    
    	/* XLOG SWITCH, alone among xlog record types, has no data */
    	rdata.buffer = InvalidBuffer;
    	rdata.data = NULL;
    	rdata.len = 0;
    	rdata.next = NULL;
    
    	RecPtr = XLogInsert(RM_XLOG_ID, XLOG_SWITCH, &rdata);
    
    	return RecPtr;
    }
    
    /*
     * Write an XLOG UNLOGGED record, indicating that some operation was
     * performed on data that we fsync()'d directly to disk, skipping
     * WAL-logging.
     *
     * Such operations screw up archive recovery, so we complain if we see
     * these records during archive recovery. That shouldn't happen in a
     * correctly configured server, but you can induce it by temporarily
     * disabling archiving and restarting, so it's good to at least get a
     * warning of silent data loss in such cases. These records serve no
     * other purpose and are simply ignored during crash recovery.
     */
    void
    XLogReportUnloggedStatement(char *reason)
    {
    	XLogRecData rdata;
    
    	rdata.buffer = InvalidBuffer;
    	rdata.data = reason;
    	rdata.len = strlen(reason) + 1;
    	rdata.next = NULL;
    
    	XLogInsert(RM_XLOG_ID, XLOG_UNLOGGED, &rdata);
    }
    
    /*
     * XLOG resource manager's routines
     *
     * Definitions of info values are in include/catalog/pg_control.h, though
     * not all record types are related to control file updates.
     */
    void
    xlog_redo(XLogRecPtr lsn, XLogRecord *record)
    {
    	uint8		info = record->xl_info & ~XLR_INFO_MASK;
    
    	/* Backup blocks are not used in xlog records */
    	Assert(!(record->xl_info & XLR_BKP_BLOCK_MASK));
    
    	if (info == XLOG_NEXTOID)
    	{
    		Oid			nextOid;
    
    		memcpy(&nextOid, XLogRecGetData(record), sizeof(Oid));
    		if (ShmemVariableCache->nextOid < nextOid)
    		{
    			ShmemVariableCache->nextOid = nextOid;
    			ShmemVariableCache->oidCount = 0;
    		}
    	}
    	else if (info == XLOG_CHECKPOINT_SHUTDOWN)
    	{
    		CheckPoint	checkPoint;
    
    		memcpy(&checkPoint, XLogRecGetData(record), sizeof(CheckPoint));
    		/* In a SHUTDOWN checkpoint, believe the counters exactly */
    		ShmemVariableCache->nextXid = checkPoint.nextXid;
    		ShmemVariableCache->nextOid = checkPoint.nextOid;
    		ShmemVariableCache->oidCount = 0;
    		MultiXactSetNextMXact(checkPoint.nextMulti,
    							  checkPoint.nextMultiOffset);
    		SetTransactionIdLimit(checkPoint.oldestXid, checkPoint.oldestXidDB);
    
    		/* Check to see if any changes to max_connections give problems */
    		if (standbyState != STANDBY_DISABLED)
    			CheckRequiredParameterValues(checkPoint);
    
    		if (standbyState >= STANDBY_INITIALIZED)
    		{
    			/*
    			 * Remove stale transactions, if any.
    			 */
    			ExpireOldKnownAssignedTransactionIds(checkPoint.nextXid);
    			StandbyReleaseOldLocks(checkPoint.nextXid);
    		}
    
    		/* ControlFile->checkPointCopy always tracks the latest ckpt XID */
    		ControlFile->checkPointCopy.nextXidEpoch = checkPoint.nextXidEpoch;
    		ControlFile->checkPointCopy.nextXid = checkPoint.nextXid;
    
    		/*
    		 * TLI may change in a shutdown checkpoint, but it shouldn't decrease
    		 */
    		if (checkPoint.ThisTimeLineID != ThisTimeLineID)
    		{
    			if (checkPoint.ThisTimeLineID < ThisTimeLineID ||
    				!list_member_int(expectedTLIs,
    								 (int) checkPoint.ThisTimeLineID))
    				ereport(PANIC,
    						(errmsg("unexpected timeline ID %u (after %u) in checkpoint record",
    								checkPoint.ThisTimeLineID, ThisTimeLineID)));
    			/* Following WAL records should be run with new TLI */
    			ThisTimeLineID = checkPoint.ThisTimeLineID;
    		}
    
    		RecoveryRestartPoint(&checkPoint);
    	}
    	else if (info == XLOG_CHECKPOINT_ONLINE)
    	{
    		CheckPoint	checkPoint;
    
    		memcpy(&checkPoint, XLogRecGetData(record), sizeof(CheckPoint));
    		/* In an ONLINE checkpoint, treat the counters like NEXTOID */
    		if (TransactionIdPrecedes(ShmemVariableCache->nextXid,
    								  checkPoint.nextXid))
    			ShmemVariableCache->nextXid = checkPoint.nextXid;
    		if (ShmemVariableCache->nextOid < checkPoint.nextOid)
    		{
    			ShmemVariableCache->nextOid = checkPoint.nextOid;
    			ShmemVariableCache->oidCount = 0;
    		}
    		MultiXactAdvanceNextMXact(checkPoint.nextMulti,
    								  checkPoint.nextMultiOffset);
    		if (TransactionIdPrecedes(ShmemVariableCache->oldestXid,
    								  checkPoint.oldestXid))
    			SetTransactionIdLimit(checkPoint.oldestXid,
    								  checkPoint.oldestXidDB);
    
    		/* ControlFile->checkPointCopy always tracks the latest ckpt XID */
    		ControlFile->checkPointCopy.nextXidEpoch = checkPoint.nextXidEpoch;
    		ControlFile->checkPointCopy.nextXid = checkPoint.nextXid;
    
    		/* TLI should not change in an on-line checkpoint */
    		if (checkPoint.ThisTimeLineID != ThisTimeLineID)
    			ereport(PANIC,
    					(errmsg("unexpected timeline ID %u (should be %u) in checkpoint record",
    							checkPoint.ThisTimeLineID, ThisTimeLineID)));
    
    		RecoveryRestartPoint(&checkPoint);
    	}
    	else if (info == XLOG_NOOP)
    	{
    		/* nothing to do here */
    	}
    	else if (info == XLOG_SWITCH)
    	{
    		/* nothing to do here */
    	}
    	else if (info == XLOG_BACKUP_END)
    	{
    		XLogRecPtr	startpoint;
    
    		memcpy(&startpoint, XLogRecGetData(record), sizeof(startpoint));
    
    		if (XLByteEQ(ControlFile->backupStartPoint, startpoint))
    		{
    			/*
    			 * We have reached the end of base backup, the point where
    			 * pg_stop_backup() was done. The data on disk is now consistent.
    			 * Reset backupStartPoint, and update minRecoveryPoint to make
    			 * sure we don't allow starting up at an earlier point even if
    			 * recovery is stopped and restarted soon after this.
    			 */
    			elog(DEBUG1, "end of backup reached");
    
    			LWLockAcquire(ControlFileLock, LW_EXCLUSIVE);
    
    			if (XLByteLT(ControlFile->minRecoveryPoint, lsn))
    				ControlFile->minRecoveryPoint = lsn;
    			MemSet(&ControlFile->backupStartPoint, 0, sizeof(XLogRecPtr));
    			UpdateControlFile();
    
    			LWLockRelease(ControlFileLock);
    		}
    	}
    	else if (info == XLOG_UNLOGGED)
    	{
    		if (InArchiveRecovery)
    		{
    			/*
    			 * Note: We don't print the reason string from the record, because
    			 * that gets added as a line using xlog_desc()
    			 */
    			ereport(WARNING,
    				(errmsg("unlogged operation performed, data may be missing"),
    				 errhint("This can happen if you temporarily disable archive_mode without taking a new base backup.")));
    		}
    	}
    }
    
    void
    xlog_desc(StringInfo buf, uint8 xl_info, char *rec)
    {
    	uint8		info = xl_info & ~XLR_INFO_MASK;
    
    	if (info == XLOG_CHECKPOINT_SHUTDOWN ||
    		info == XLOG_CHECKPOINT_ONLINE)
    	{
    		CheckPoint *checkpoint = (CheckPoint *) rec;
    
    		appendStringInfo(buf, "checkpoint: redo %X/%X; "
    						 "tli %u; xid %u/%u; oid %u; multi %u; offset %u; "
    						 "oldest xid %u in DB %u; oldest running xid %u; %s",
    						 checkpoint->redo.xlogid, checkpoint->redo.xrecoff,
    						 checkpoint->ThisTimeLineID,
    						 checkpoint->nextXidEpoch, checkpoint->nextXid,
    						 checkpoint->nextOid,
    						 checkpoint->nextMulti,
    						 checkpoint->nextMultiOffset,
    						 checkpoint->oldestXid,
    						 checkpoint->oldestXidDB,
    						 checkpoint->oldestActiveXid,
    				 (info == XLOG_CHECKPOINT_SHUTDOWN) ? "shutdown" : "online");
    	}
    	else if (info == XLOG_NOOP)
    	{
    		appendStringInfo(buf, "xlog no-op");
    	}
    	else if (info == XLOG_NEXTOID)
    	{
    		Oid			nextOid;
    
    		memcpy(&nextOid, rec, sizeof(Oid));
    		appendStringInfo(buf, "nextOid: %u", nextOid);
    	}
    	else if (info == XLOG_SWITCH)
    	{
    		appendStringInfo(buf, "xlog switch");
    	}
    	else if (info == XLOG_BACKUP_END)
    	{
    		XLogRecPtr	startpoint;
    
    		memcpy(&startpoint, rec, sizeof(XLogRecPtr));
    		appendStringInfo(buf, "backup end: %X/%X",
    						 startpoint.xlogid, startpoint.xrecoff);
    	}
    	else if (info == XLOG_UNLOGGED)
    	{
    		char	   *reason = rec;
    
    		appendStringInfo(buf, "unlogged operation: %s", reason);
    	}
    	else
    		appendStringInfo(buf, "UNKNOWN");
    }
    
    #ifdef WAL_DEBUG
    
    static void
    xlog_outrec(StringInfo buf, XLogRecord *record)
    {
    	int			i;
    
    	appendStringInfo(buf, "prev %X/%X; xid %u",
    					 record->xl_prev.xlogid, record->xl_prev.xrecoff,
    					 record->xl_xid);
    
    	appendStringInfo(buf, "; len %u",
    					 record->xl_len);
    
    	for (i = 0; i < XLR_MAX_BKP_BLOCKS; i++)
    	{
    		if (record->xl_info & XLR_SET_BKP_BLOCK(i))
    			appendStringInfo(buf, "; bkpb%d", i + 1);
    	}
    
    	appendStringInfo(buf, ": %s", RmgrTable[record->xl_rmid].rm_name);
    }
    #endif   /* WAL_DEBUG */
    
    
    /*
     * Return the (possible) sync flag used for opening a file, depending on the
     * value of the GUC wal_sync_method.
     */
    static int
    get_sync_bit(int method)
    {
    	int			o_direct_flag = 0;
    
    	/* If fsync is disabled, never open in sync mode */
    	if (!enableFsync)
    		return 0;
    
    	/*
    	 * Optimize writes by bypassing kernel cache with O_DIRECT when using
    	 * O_SYNC, O_DSYNC or O_FSYNC. But only if archiving and streaming are
    	 * disabled, otherwise the archive command or walsender process will read
    	 * the WAL soon after writing it, which is guaranteed to cause a physical
    	 * read if we bypassed the kernel cache. We also skip the
    	 * posix_fadvise(POSIX_FADV_DONTNEED) call in XLogFileClose() for the same
    	 * reason.
    	 *
    	 * Never use O_DIRECT in walreceiver process for similar reasons; the WAL
    	 * written by walreceiver is normally read by the startup process soon
    	 * after its written. Also, walreceiver performs unaligned writes, which
    	 * don't work with O_DIRECT, so it is required for correctness too.
    	 */
    	if (!XLogIsNeeded() && !am_walreceiver)
    		o_direct_flag = PG_O_DIRECT;
    
    	switch (method)
    	{
    			/*
    			 * enum values for all sync options are defined even if they are
    			 * not supported on the current platform.  But if not, they are
    			 * not included in the enum option array, and therefore will never
    			 * be seen here.
    			 */
    		case SYNC_METHOD_FSYNC:
    		case SYNC_METHOD_FSYNC_WRITETHROUGH:
    		case SYNC_METHOD_FDATASYNC:
    			return 0;
    #ifdef OPEN_SYNC_FLAG
    		case SYNC_METHOD_OPEN:
    			return OPEN_SYNC_FLAG | o_direct_flag;
    #endif
    #ifdef OPEN_DATASYNC_FLAG
    		case SYNC_METHOD_OPEN_DSYNC:
    			return OPEN_DATASYNC_FLAG | o_direct_flag;
    #endif
    		default:
    			/* can't happen (unless we are out of sync with option array) */
    			elog(ERROR, "unrecognized wal_sync_method: %d", method);
    			return 0;			/* silence warning */
    	}
    }
    
    /*
     * GUC support
     */
    bool
    assign_xlog_sync_method(int new_sync_method, bool doit, GucSource source)
    {
    	if (!doit)
    		return true;
    
    	if (sync_method != new_sync_method)
    	{
    		/*
    		 * To ensure that no blocks escape unsynced, force an fsync on the
    		 * currently open log segment (if any).  Also, if the open flag is
    		 * changing, close the log file so it will be reopened (with new flag
    		 * bit) at next use.
    		 */
    		if (openLogFile >= 0)
    		{
    			if (pg_fsync(openLogFile) != 0)
    				ereport(PANIC,
    						(errcode_for_file_access(),
    						 errmsg("could not fsync log file %u, segment %u: %m",
    								openLogId, openLogSeg)));
    			if (get_sync_bit(sync_method) != get_sync_bit(new_sync_method))
    				XLogFileClose();
    		}
    	}
    
    	return true;
    }
    
    
    /*
     * Issue appropriate kind of fsync (if any) for an XLOG output file.
     *
     * 'fd' is a file descriptor for the XLOG file to be fsync'd.
     * 'log' and 'seg' are for error reporting purposes.
     */
    void
    issue_xlog_fsync(int fd, uint32 log, uint32 seg)
    {
    	switch (sync_method)
    	{
    		case SYNC_METHOD_FSYNC:
    			if (pg_fsync_no_writethrough(fd) != 0)
    				ereport(PANIC,
    						(errcode_for_file_access(),
    						 errmsg("could not fsync log file %u, segment %u: %m",
    								log, seg)));
    			break;
    #ifdef HAVE_FSYNC_WRITETHROUGH
    		case SYNC_METHOD_FSYNC_WRITETHROUGH:
    			if (pg_fsync_writethrough(fd) != 0)
    				ereport(PANIC,
    						(errcode_for_file_access(),
    						 errmsg("could not fsync write-through log file %u, segment %u: %m",
    								log, seg)));
    			break;
    #endif
    #ifdef HAVE_FDATASYNC
    		case SYNC_METHOD_FDATASYNC:
    			if (pg_fdatasync(fd) != 0)
    				ereport(PANIC,
    						(errcode_for_file_access(),
    					errmsg("could not fdatasync log file %u, segment %u: %m",
    						   log, seg)));
    			break;
    #endif
    		case SYNC_METHOD_OPEN:
    		case SYNC_METHOD_OPEN_DSYNC:
    			/* write synced it already */
    			break;
    		default:
    			elog(PANIC, "unrecognized wal_sync_method: %d", sync_method);
    			break;
    	}
    }
    
    
    /*
     * pg_start_backup: set up for taking an on-line backup dump
     *
     * Essentially what this does is to create a backup label file in $PGDATA,
     * where it will be archived as part of the backup dump.  The label file
     * contains the user-supplied label string (typically this would be used
     * to tell where the backup dump will be stored) and the starting time and
     * starting WAL location for the dump.
     */
    Datum
    pg_start_backup(PG_FUNCTION_ARGS)
    {
    	text	   *backupid = PG_GETARG_TEXT_P(0);
    	bool		fast = PG_GETARG_BOOL(1);
    	char	   *backupidstr;
    	XLogRecPtr	checkpointloc;
    	XLogRecPtr	startpoint;
    	pg_time_t	stamp_time;
    	char		strfbuf[128];
    	char		xlogfilename[MAXFNAMELEN];
    	uint32		_logId;
    	uint32		_logSeg;
    	struct stat stat_buf;
    	FILE	   *fp;
    
    	if (!superuser())
    		ereport(ERROR,
    				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
    				 errmsg("must be superuser to run a backup")));
    
    	if (RecoveryInProgress())
    		ereport(ERROR,
    				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
    				 errmsg("recovery is in progress"),
    				 errhint("WAL control functions cannot be executed during recovery.")));
    
    	if (!XLogArchivingActive())
    		ereport(ERROR,
    				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
    				 errmsg("WAL archiving is not active"),
    				 errhint("archive_mode must be enabled at server start.")));
    
    	if (!XLogArchiveCommandSet())
    		ereport(ERROR,
    				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
    				 errmsg("WAL archiving is not active"),
    				 errhint("archive_command must be defined before "
    						 "online backups can be made safely.")));
    
    	backupidstr = text_to_cstring(backupid);
    
    	/*
    	 * Mark backup active in shared memory.  We must do full-page WAL writes
    	 * during an on-line backup even if not doing so at other times, because
    	 * it's quite possible for the backup dump to obtain a "torn" (partially
    	 * written) copy of a database page if it reads the page concurrently with
    	 * our write to the same page.	This can be fixed as long as the first
    	 * write to the page in the WAL sequence is a full-page write. Hence, we
    	 * turn on forcePageWrites and then force a CHECKPOINT, to ensure there
    	 * are no dirty pages in shared memory that might get dumped while the
    	 * backup is in progress without having a corresponding WAL record.  (Once
    	 * the backup is complete, we need not force full-page writes anymore,
    	 * since we expect that any pages not modified during the backup interval
    	 * must have been correctly captured by the backup.)
    	 *
    	 * We must hold WALInsertLock to change the value of forcePageWrites, to
    	 * ensure adequate interlocking against XLogInsert().
    	 */
    	LWLockAcquire(WALInsertLock, LW_EXCLUSIVE);
    	if (XLogCtl->Insert.forcePageWrites)
    	{
    		LWLockRelease(WALInsertLock);
    		ereport(ERROR,
    				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
    				 errmsg("a backup is already in progress"),
    				 errhint("Run pg_stop_backup() and try again.")));
    	}
    	XLogCtl->Insert.forcePageWrites = true;
    	LWLockRelease(WALInsertLock);
    
    	/*
    	 * Force an XLOG file switch before the checkpoint, to ensure that the WAL
    	 * segment the checkpoint is written to doesn't contain pages with old
    	 * timeline IDs. That would otherwise happen if you called
    	 * pg_start_backup() right after restoring from a PITR archive: the first
    	 * WAL segment containing the startup checkpoint has pages in the
    	 * beginning with the old timeline ID. That can cause trouble at recovery:
    	 * we won't have a history file covering the old timeline if pg_xlog
    	 * directory was not included in the base backup and the WAL archive was
    	 * cleared too before starting the backup.
    	 */
    	RequestXLogSwitch();
    
    	/* Ensure we release forcePageWrites if fail below */
    	PG_ENSURE_ERROR_CLEANUP(pg_start_backup_callback, (Datum) 0);
    	{
    		/*
    		 * Force a CHECKPOINT.	Aside from being necessary to prevent torn
    		 * page problems, this guarantees that two successive backup runs will
    		 * have different checkpoint positions and hence different history
    		 * file names, even if nothing happened in between.
    		 *
    		 * We use CHECKPOINT_IMMEDIATE only if requested by user (via passing
    		 * fast = true).  Otherwise this can take awhile.
    		 */
    		RequestCheckpoint(CHECKPOINT_FORCE | CHECKPOINT_WAIT |
    						  (fast ? CHECKPOINT_IMMEDIATE : 0));
    
    		/*
    		 * Now we need to fetch the checkpoint record location, and also its
    		 * REDO pointer.  The oldest point in WAL that would be needed to
    		 * restore starting from the checkpoint is precisely the REDO pointer.
    		 */
    		LWLockAcquire(ControlFileLock, LW_SHARED);
    		checkpointloc = ControlFile->checkPoint;
    		startpoint = ControlFile->checkPointCopy.redo;
    		LWLockRelease(ControlFileLock);
    
    		XLByteToSeg(startpoint, _logId, _logSeg);
    		XLogFileName(xlogfilename, ThisTimeLineID, _logId, _logSeg);
    
    		/* Use the log timezone here, not the session timezone */
    		stamp_time = (pg_time_t) time(NULL);
    		pg_strftime(strfbuf, sizeof(strfbuf),
    					"%Y-%m-%d %H:%M:%S %Z",
    					pg_localtime(&stamp_time, log_timezone));
    
    		/*
    		 * Check for existing backup label --- implies a backup is already
    		 * running.  (XXX given that we checked forcePageWrites above, maybe
    		 * it would be OK to just unlink any such label file?)
    		 */
    		if (stat(BACKUP_LABEL_FILE, &stat_buf) != 0)
    		{
    			if (errno != ENOENT)
    				ereport(ERROR,
    						(errcode_for_file_access(),
    						 errmsg("could not stat file \"%s\": %m",
    								BACKUP_LABEL_FILE)));
    		}
    		else
    			ereport(ERROR,
    					(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
    					 errmsg("a backup is already in progress"),
    					 errhint("If you're sure there is no backup in progress, remove file \"%s\" and try again.",
    							 BACKUP_LABEL_FILE)));
    
    		/*
    		 * Okay, write the file
    		 */
    		fp = AllocateFile(BACKUP_LABEL_FILE, "w");
    		if (!fp)
    			ereport(ERROR,
    					(errcode_for_file_access(),
    					 errmsg("could not create file \"%s\": %m",
    							BACKUP_LABEL_FILE)));
    		fprintf(fp, "START WAL LOCATION: %X/%X (file %s)\n",
    				startpoint.xlogid, startpoint.xrecoff, xlogfilename);
    		fprintf(fp, "CHECKPOINT LOCATION: %X/%X\n",
    				checkpointloc.xlogid, checkpointloc.xrecoff);
    		fprintf(fp, "START TIME: %s\n", strfbuf);
    		fprintf(fp, "LABEL: %s\n", backupidstr);
    		if (fflush(fp) || ferror(fp) || FreeFile(fp))
    			ereport(ERROR,
    					(errcode_for_file_access(),
    					 errmsg("could not write file \"%s\": %m",
    							BACKUP_LABEL_FILE)));
    	}
    	PG_END_ENSURE_ERROR_CLEANUP(pg_start_backup_callback, (Datum) 0);
    
    	/*
    	 * We're done.  As a convenience, return the starting WAL location.
    	 */
    	snprintf(xlogfilename, sizeof(xlogfilename), "%X/%X",
    			 startpoint.xlogid, startpoint.xrecoff);
    	PG_RETURN_TEXT_P(cstring_to_text(xlogfilename));
    }
    
    /* Error cleanup callback for pg_start_backup */
    static void
    pg_start_backup_callback(int code, Datum arg)
    {
    	/* Turn off forcePageWrites on failure */
    	LWLockAcquire(WALInsertLock, LW_EXCLUSIVE);
    	XLogCtl->Insert.forcePageWrites = false;
    	LWLockRelease(WALInsertLock);
    }
    
    /*
     * pg_stop_backup: finish taking an on-line backup dump
     *
     * We write an end-of-backup WAL record, and remove the backup label file
     * created by pg_start_backup, creating a backup history file in pg_xlog
     * instead (whence it will immediately be archived). The backup history file
     * contains the same info found in the label file, plus the backup-end time
     * and WAL location. Before 9.0, the backup-end time was read from the backup
     * history file at the beginning of archive recovery, but we now use the WAL
     * record for that and the file is for informational and debug purposes only.
     *
     * Note: different from CancelBackup which just cancels online backup mode.
     */
    Datum
    pg_stop_backup(PG_FUNCTION_ARGS)
    {
    	XLogRecPtr	startpoint;
    	XLogRecPtr	stoppoint;
    	XLogRecData rdata;
    	pg_time_t	stamp_time;
    	char		strfbuf[128];
    	char		histfilepath[MAXPGPATH];
    	char		startxlogfilename[MAXFNAMELEN];
    	char		stopxlogfilename[MAXFNAMELEN];
    	char		lastxlogfilename[MAXFNAMELEN];
    	char		histfilename[MAXFNAMELEN];
    	uint32		_logId;
    	uint32		_logSeg;
    	FILE	   *lfp;
    	FILE	   *fp;
    	char		ch;
    	int			ich;
    	int			seconds_before_warning;
    	int			waits = 0;
    
    	if (!superuser())
    		ereport(ERROR,
    				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
    				 (errmsg("must be superuser to run a backup"))));
    
    	if (RecoveryInProgress())
    		ereport(ERROR,
    				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
    				 errmsg("recovery is in progress"),
    				 errhint("WAL control functions cannot be executed during recovery.")));
    
    	if (!XLogArchivingActive())
    		ereport(ERROR,
    				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
    				 errmsg("WAL archiving is not active"),
    				 errhint("archive_mode must be enabled at server start.")));
    
    	/*
    	 * OK to clear forcePageWrites
    	 */
    	LWLockAcquire(WALInsertLock, LW_EXCLUSIVE);
    	XLogCtl->Insert.forcePageWrites = false;
    	LWLockRelease(WALInsertLock);
    
    	/*
    	 * Open the existing label file
    	 */
    	lfp = AllocateFile(BACKUP_LABEL_FILE, "r");
    	if (!lfp)
    	{
    		if (errno != ENOENT)
    			ereport(ERROR,
    					(errcode_for_file_access(),
    					 errmsg("could not read file \"%s\": %m",
    							BACKUP_LABEL_FILE)));
    		ereport(ERROR,
    				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
    				 errmsg("a backup is not in progress")));
    	}
    
    	/*
    	 * Read and parse the START WAL LOCATION line (this code is pretty crude,
    	 * but we are not expecting any variability in the file format).
    	 */
    	if (fscanf(lfp, "START WAL LOCATION: %X/%X (file %24s)%c",
    			   &startpoint.xlogid, &startpoint.xrecoff, startxlogfilename,
    			   &ch) != 4 || ch != '\n')
    		ereport(ERROR,
    				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
    				 errmsg("invalid data in file \"%s\"", BACKUP_LABEL_FILE)));
    
    	/*
    	 * Write the backup-end xlog record
    	 */
    	rdata.data = (char *) (&startpoint);
    	rdata.len = sizeof(startpoint);
    	rdata.buffer = InvalidBuffer;
    	rdata.next = NULL;
    	stoppoint = XLogInsert(RM_XLOG_ID, XLOG_BACKUP_END, &rdata);
    
    	/*
    	 * Force a switch to a new xlog segment file, so that the backup is valid
    	 * as soon as archiver moves out the current segment file.
    	 */
    	RequestXLogSwitch();
    
    	XLByteToPrevSeg(stoppoint, _logId, _logSeg);
    	XLogFileName(stopxlogfilename, ThisTimeLineID, _logId, _logSeg);
    
    	/* Use the log timezone here, not the session timezone */
    	stamp_time = (pg_time_t) time(NULL);
    	pg_strftime(strfbuf, sizeof(strfbuf),
    				"%Y-%m-%d %H:%M:%S %Z",
    				pg_localtime(&stamp_time, log_timezone));
    
    	/*
    	 * Write the backup history file
    	 */
    	XLByteToSeg(startpoint, _logId, _logSeg);
    	BackupHistoryFilePath(histfilepath, ThisTimeLineID, _logId, _logSeg,
    						  startpoint.xrecoff % XLogSegSize);
    	fp = AllocateFile(histfilepath, "w");
    	if (!fp)
    		ereport(ERROR,
    				(errcode_for_file_access(),
    				 errmsg("could not create file \"%s\": %m",
    						histfilepath)));
    	fprintf(fp, "START WAL LOCATION: %X/%X (file %s)\n",
    			startpoint.xlogid, startpoint.xrecoff, startxlogfilename);
    	fprintf(fp, "STOP WAL LOCATION: %X/%X (file %s)\n",
    			stoppoint.xlogid, stoppoint.xrecoff, stopxlogfilename);
    	/* transfer remaining lines from label to history file */
    	while ((ich = fgetc(lfp)) != EOF)
    		fputc(ich, fp);
    	fprintf(fp, "STOP TIME: %s\n", strfbuf);
    	if (fflush(fp) || ferror(fp) || FreeFile(fp))
    		ereport(ERROR,
    				(errcode_for_file_access(),
    				 errmsg("could not write file \"%s\": %m",
    						histfilepath)));
    
    	/*
    	 * Close and remove the backup label file
    	 */
    	if (ferror(lfp) || FreeFile(lfp))
    		ereport(ERROR,
    				(errcode_for_file_access(),
    				 errmsg("could not read file \"%s\": %m",
    						BACKUP_LABEL_FILE)));
    	if (unlink(BACKUP_LABEL_FILE) != 0)
    		ereport(ERROR,
    				(errcode_for_file_access(),
    				 errmsg("could not remove file \"%s\": %m",
    						BACKUP_LABEL_FILE)));
    
    	/*
    	 * Clean out any no-longer-needed history files.  As a side effect, this
    	 * will post a .ready file for the newly created history file, notifying
    	 * the archiver that history file may be archived immediately.
    	 */
    	CleanupBackupHistory();
    
    	/*
    	 * Wait until both the last WAL file filled during backup and the history
    	 * file have been archived.  We assume that the alphabetic sorting
    	 * property of the WAL files ensures any earlier WAL files are safely
    	 * archived as well.
    	 *
    	 * We wait forever, since archive_command is supposed to work and we
    	 * assume the admin wanted his backup to work completely. If you don't
    	 * wish to wait, you can set statement_timeout.  Also, some notices are
    	 * issued to clue in anyone who might be doing this interactively.
    	 */
    	XLByteToPrevSeg(stoppoint, _logId, _logSeg);
    	XLogFileName(lastxlogfilename, ThisTimeLineID, _logId, _logSeg);
    
    	XLByteToSeg(startpoint, _logId, _logSeg);
    	BackupHistoryFileName(histfilename, ThisTimeLineID, _logId, _logSeg,
    						  startpoint.xrecoff % XLogSegSize);
    
    	ereport(NOTICE,
    			(errmsg("pg_stop_backup cleanup done, waiting for required WAL segments to be archived")));
    
    	seconds_before_warning = 60;
    	waits = 0;
    
    	while (XLogArchiveIsBusy(lastxlogfilename) ||
    		   XLogArchiveIsBusy(histfilename))
    	{
    		CHECK_FOR_INTERRUPTS();
    
    		pg_usleep(1000000L);
    
    		if (++waits >= seconds_before_warning)
    		{
    			seconds_before_warning *= 2;		/* This wraps in >10 years... */
    			ereport(WARNING,
    					(errmsg("pg_stop_backup still waiting for all required WAL segments to be archived (%d seconds elapsed)",
    							waits),
    			errhint("Check that your archive_command is executing properly. "
    					"pg_stop_backup can be cancelled safely, "
    					"but the database backup will not be usable without all the WAL segments.")));
    		}
    	}
    
    	/*
    	 * We're done.  As a convenience, return the ending WAL location.
    	 */
    	snprintf(stopxlogfilename, sizeof(stopxlogfilename), "%X/%X",
    			 stoppoint.xlogid, stoppoint.xrecoff);
    	PG_RETURN_TEXT_P(cstring_to_text(stopxlogfilename));
    }
    
    /*
     * pg_switch_xlog: switch to next xlog file
     */
    Datum
    pg_switch_xlog(PG_FUNCTION_ARGS)
    {
    	XLogRecPtr	switchpoint;
    	char		location[MAXFNAMELEN];
    
    	if (!superuser())
    		ereport(ERROR,
    				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
    			 (errmsg("must be superuser to switch transaction log files"))));
    
    	if (RecoveryInProgress())
    		ereport(ERROR,
    				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
    				 errmsg("recovery is in progress"),
    				 errhint("WAL control functions cannot be executed during recovery.")));
    
    	switchpoint = RequestXLogSwitch();
    
    	/*
    	 * As a convenience, return the WAL location of the switch record
    	 */
    	snprintf(location, sizeof(location), "%X/%X",
    			 switchpoint.xlogid, switchpoint.xrecoff);
    	PG_RETURN_TEXT_P(cstring_to_text(location));
    }
    
    /*
     * Report the current WAL write location (same format as pg_start_backup etc)
     *
     * This is useful for determining how much of WAL is visible to an external
     * archiving process.  Note that the data before this point is written out
     * to the kernel, but is not necessarily synced to disk.
     */
    Datum
    pg_current_xlog_location(PG_FUNCTION_ARGS)
    {
    	char		location[MAXFNAMELEN];
    
    	if (RecoveryInProgress())
    		ereport(ERROR,
    				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
    				 errmsg("recovery is in progress"),
    				 errhint("WAL control functions cannot be executed during recovery.")));
    
    	/* Make sure we have an up-to-date local LogwrtResult */
    	{
    		/* use volatile pointer to prevent code rearrangement */
    		volatile XLogCtlData *xlogctl = XLogCtl;
    
    		SpinLockAcquire(&xlogctl->info_lck);
    		LogwrtResult = xlogctl->LogwrtResult;
    		SpinLockRelease(&xlogctl->info_lck);
    	}
    
    	snprintf(location, sizeof(location), "%X/%X",
    			 LogwrtResult.Write.xlogid, LogwrtResult.Write.xrecoff);
    	PG_RETURN_TEXT_P(cstring_to_text(location));
    }
    
    /*
     * Report the current WAL insert location (same format as pg_start_backup etc)
     *
     * This function is mostly for debugging purposes.
     */
    Datum
    pg_current_xlog_insert_location(PG_FUNCTION_ARGS)
    {
    	XLogCtlInsert *Insert = &XLogCtl->Insert;
    	XLogRecPtr	current_recptr;
    	char		location[MAXFNAMELEN];
    
    	if (RecoveryInProgress())
    		ereport(ERROR,
    				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
    				 errmsg("recovery is in progress"),
    				 errhint("WAL control functions cannot be executed during recovery.")));
    
    	/*
    	 * Get the current end-of-WAL position ... shared lock is sufficient
    	 */
    	LWLockAcquire(WALInsertLock, LW_SHARED);
    	INSERT_RECPTR(current_recptr, Insert, Insert->curridx);
    	LWLockRelease(WALInsertLock);
    
    	snprintf(location, sizeof(location), "%X/%X",
    			 current_recptr.xlogid, current_recptr.xrecoff);
    	PG_RETURN_TEXT_P(cstring_to_text(location));
    }
    
    /*
     * Report the last WAL receive location (same format as pg_start_backup etc)
     *
     * This is useful for determining how much of WAL is guaranteed to be received
     * and synced to disk by walreceiver.
     */
    Datum
    pg_last_xlog_receive_location(PG_FUNCTION_ARGS)
    {
    	XLogRecPtr	recptr;
    	char		location[MAXFNAMELEN];
    
    	recptr = GetWalRcvWriteRecPtr();
    
    	snprintf(location, sizeof(location), "%X/%X",
    			 recptr.xlogid, recptr.xrecoff);
    	PG_RETURN_TEXT_P(cstring_to_text(location));
    }
    
    /*
     * Report the last WAL replay location (same format as pg_start_backup etc)
     *
     * This is useful for determining how much of WAL is visible to read-only
     * connections during recovery.
     */
    Datum
    pg_last_xlog_replay_location(PG_FUNCTION_ARGS)
    {
    	/* use volatile pointer to prevent code rearrangement */
    	volatile XLogCtlData *xlogctl = XLogCtl;
    	XLogRecPtr	recptr;
    	char		location[MAXFNAMELEN];
    
    	SpinLockAcquire(&xlogctl->info_lck);
    	recptr = xlogctl->recoveryLastRecPtr;
    	SpinLockRelease(&xlogctl->info_lck);
    
    	snprintf(location, sizeof(location), "%X/%X",
    			 recptr.xlogid, recptr.xrecoff);
    	PG_RETURN_TEXT_P(cstring_to_text(location));
    }
    
    /*
     * Compute an xlog file name and decimal byte offset given a WAL location,
     * such as is returned by pg_stop_backup() or pg_xlog_switch().
     *
     * Note that a location exactly at a segment boundary is taken to be in
     * the previous segment.  This is usually the right thing, since the
     * expected usage is to determine which xlog file(s) are ready to archive.
     */
    Datum
    pg_xlogfile_name_offset(PG_FUNCTION_ARGS)
    {
    	text	   *location = PG_GETARG_TEXT_P(0);
    	char	   *locationstr;
    	unsigned int uxlogid;
    	unsigned int uxrecoff;
    	uint32		xlogid;
    	uint32		xlogseg;
    	uint32		xrecoff;
    	XLogRecPtr	locationpoint;
    	char		xlogfilename[MAXFNAMELEN];
    	Datum		values[2];
    	bool		isnull[2];
    	TupleDesc	resultTupleDesc;
    	HeapTuple	resultHeapTuple;
    	Datum		result;
    
    	/*
    	 * Read input and parse
    	 */
    	locationstr = text_to_cstring(location);
    
    	if (sscanf(locationstr, "%X/%X", &uxlogid, &uxrecoff) != 2)
    		ereport(ERROR,
    				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
    				 errmsg("could not parse transaction log location \"%s\"",
    						locationstr)));
    
    	locationpoint.xlogid = uxlogid;
    	locationpoint.xrecoff = uxrecoff;
    
    	/*
    	 * Construct a tuple descriptor for the result row.  This must match this
    	 * function's pg_proc entry!
    	 */
    	resultTupleDesc = CreateTemplateTupleDesc(2, false);
    	TupleDescInitEntry(resultTupleDesc, (AttrNumber) 1, "file_name",
    					   TEXTOID, -1, 0);
    	TupleDescInitEntry(resultTupleDesc, (AttrNumber) 2, "file_offset",
    					   INT4OID, -1, 0);
    
    	resultTupleDesc = BlessTupleDesc(resultTupleDesc);
    
    	/*
    	 * xlogfilename
    	 */
    	XLByteToPrevSeg(locationpoint, xlogid, xlogseg);
    	XLogFileName(xlogfilename, ThisTimeLineID, xlogid, xlogseg);
    
    	values[0] = CStringGetTextDatum(xlogfilename);
    	isnull[0] = false;
    
    	/*
    	 * offset
    	 */
    	xrecoff = locationpoint.xrecoff - xlogseg * XLogSegSize;
    
    	values[1] = UInt32GetDatum(xrecoff);
    	isnull[1] = false;
    
    	/*
    	 * Tuple jam: Having first prepared your Datums, then squash together
    	 */
    	resultHeapTuple = heap_form_tuple(resultTupleDesc, values, isnull);
    
    	result = HeapTupleGetDatum(resultHeapTuple);
    
    	PG_RETURN_DATUM(result);
    }
    
    /*
     * Compute an xlog file name given a WAL location,
     * such as is returned by pg_stop_backup() or pg_xlog_switch().
     */
    Datum
    pg_xlogfile_name(PG_FUNCTION_ARGS)
    {
    	text	   *location = PG_GETARG_TEXT_P(0);
    	char	   *locationstr;
    	unsigned int uxlogid;
    	unsigned int uxrecoff;
    	uint32		xlogid;
    	uint32		xlogseg;
    	XLogRecPtr	locationpoint;
    	char		xlogfilename[MAXFNAMELEN];
    
    	locationstr = text_to_cstring(location);
    
    	if (sscanf(locationstr, "%X/%X", &uxlogid, &uxrecoff) != 2)
    		ereport(ERROR,
    				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
    				 errmsg("could not parse transaction log location \"%s\"",
    						locationstr)));
    
    	locationpoint.xlogid = uxlogid;
    	locationpoint.xrecoff = uxrecoff;
    
    	XLByteToPrevSeg(locationpoint, xlogid, xlogseg);
    	XLogFileName(xlogfilename, ThisTimeLineID, xlogid, xlogseg);
    
    	PG_RETURN_TEXT_P(cstring_to_text(xlogfilename));
    }
    
    /*
     * read_backup_label: check to see if a backup_label file is present
     *
     * If we see a backup_label during recovery, we assume that we are recovering
     * from a backup dump file, and we therefore roll forward from the checkpoint
     * identified by the label file, NOT what pg_control says.	This avoids the
     * problem that pg_control might have been archived one or more checkpoints
     * later than the start of the dump, and so if we rely on it as the start
     * point, we will fail to restore a consistent database state.
     *
     * Returns TRUE if a backup_label was found (and fills the checkpoint
     * location and its REDO location into *checkPointLoc and RedoStartLSN,
     * respectively); returns FALSE if not.
     */
    static bool
    read_backup_label(XLogRecPtr *checkPointLoc)
    {
    	char		startxlogfilename[MAXFNAMELEN];
    	TimeLineID	tli;
    	FILE	   *lfp;
    	char		ch;
    
    	/*
    	 * See if label file is present
    	 */
    	lfp = AllocateFile(BACKUP_LABEL_FILE, "r");
    	if (!lfp)
    	{
    		if (errno != ENOENT)
    			ereport(FATAL,
    					(errcode_for_file_access(),
    					 errmsg("could not read file \"%s\": %m",
    							BACKUP_LABEL_FILE)));
    		return false;			/* it's not there, all is fine */
    	}
    
    	/*
    	 * Read and parse the START WAL LOCATION and CHECKPOINT lines (this code
    	 * is pretty crude, but we are not expecting any variability in the file
    	 * format).
    	 */
    	if (fscanf(lfp, "START WAL LOCATION: %X/%X (file %08X%16s)%c",
    			   &RedoStartLSN.xlogid, &RedoStartLSN.xrecoff, &tli,
    			   startxlogfilename, &ch) != 5 || ch != '\n')
    		ereport(FATAL,
    				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
    				 errmsg("invalid data in file \"%s\"", BACKUP_LABEL_FILE)));
    	if (fscanf(lfp, "CHECKPOINT LOCATION: %X/%X%c",
    			   &checkPointLoc->xlogid, &checkPointLoc->xrecoff,
    			   &ch) != 3 || ch != '\n')
    		ereport(FATAL,
    				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
    				 errmsg("invalid data in file \"%s\"", BACKUP_LABEL_FILE)));
    	if (ferror(lfp) || FreeFile(lfp))
    		ereport(FATAL,
    				(errcode_for_file_access(),
    				 errmsg("could not read file \"%s\": %m",
    						BACKUP_LABEL_FILE)));
    
    	return true;
    }
    
    /*
     * Error context callback for errors occurring during rm_redo().
     */
    static void
    rm_redo_error_callback(void *arg)
    {
    	XLogRecord *record = (XLogRecord *) arg;
    	StringInfoData buf;
    
    	initStringInfo(&buf);
    	RmgrTable[record->xl_rmid].rm_desc(&buf,
    									   record->xl_info,
    									   XLogRecGetData(record));
    
    	/* don't bother emitting empty description */
    	if (buf.len > 0)
    		errcontext("xlog redo %s", buf.data);
    
    	pfree(buf.data);
    }
    
    /*
     * BackupInProgress: check if online backup mode is active
     *
     * This is done by checking for existence of the "backup_label" file.
     */
    bool
    BackupInProgress(void)
    {
    	struct stat stat_buf;
    
    	return (stat(BACKUP_LABEL_FILE, &stat_buf) == 0);
    }
    
    /*
     * CancelBackup: rename the "backup_label" file to cancel backup mode
     *
     * If the "backup_label" file exists, it will be renamed to "backup_label.old".
     * Note that this will render an online backup in progress useless.
     * To correctly finish an online backup, pg_stop_backup must be called.
     */
    void
    CancelBackup(void)
    {
    	struct stat stat_buf;
    
    	/* if the file is not there, return */
    	if (stat(BACKUP_LABEL_FILE, &stat_buf) < 0)
    		return;
    
    	/* remove leftover file from previously cancelled backup if it exists */
    	unlink(BACKUP_LABEL_OLD);
    
    	if (rename(BACKUP_LABEL_FILE, BACKUP_LABEL_OLD) == 0)
    	{
    		ereport(LOG,
    				(errmsg("online backup mode cancelled"),
    				 errdetail("\"%s\" was renamed to \"%s\".",
    						   BACKUP_LABEL_FILE, BACKUP_LABEL_OLD)));
    	}
    	else
    	{
    		ereport(WARNING,
    				(errcode_for_file_access(),
    				 errmsg("online backup mode was not cancelled"),
    				 errdetail("Could not rename \"%s\" to \"%s\": %m.",
    						   BACKUP_LABEL_FILE, BACKUP_LABEL_OLD)));
    	}
    }
    
    /* ------------------------------------------------------
     *	Startup Process main entry point and signal handlers
     * ------------------------------------------------------
     */
    
    /*
     * startupproc_quickdie() occurs when signalled SIGQUIT by the postmaster.
     *
     * Some backend has bought the farm,
     * so we need to stop what we're doing and exit.
     */
    static void
    startupproc_quickdie(SIGNAL_ARGS)
    {
    	PG_SETMASK(&BlockSig);
    
    	/*
    	 * We DO NOT want to run proc_exit() callbacks -- we're here because
    	 * shared memory may be corrupted, so we don't want to try to clean up our
    	 * transaction.  Just nail the windows shut and get out of town.  Now that
    	 * there's an atexit callback to prevent third-party code from breaking
    	 * things by calling exit() directly, we have to reset the callbacks
    	 * explicitly to make this work as intended.
    	 */
    	on_exit_reset();
    
    	/*
    	 * Note we do exit(2) not exit(0).	This is to force the postmaster into a
    	 * system reset cycle if some idiot DBA sends a manual SIGQUIT to a random
    	 * backend.  This is necessary precisely because we don't clean up our
    	 * shared memory state.  (The "dead man switch" mechanism in pmsignal.c
    	 * should ensure the postmaster sees this as a crash, too, but no harm in
    	 * being doubly sure.)
    	 */
    	exit(2);
    }
    
    
    /* SIGHUP: set flag to re-read config file at next convenient time */
    static void
    StartupProcSigHupHandler(SIGNAL_ARGS)
    {
    	got_SIGHUP = true;
    }
    
    /* SIGTERM: set flag to abort redo and exit */
    static void
    StartupProcShutdownHandler(SIGNAL_ARGS)
    {
    	if (in_restore_command)
    		proc_exit(1);
    	else
    		shutdown_requested = true;
    }
    
    /* Handle SIGHUP and SIGTERM signals of startup process */
    void
    HandleStartupProcInterrupts(void)
    {
    	/*
    	 * Check if we were requested to re-read config file.
    	 */
    	if (got_SIGHUP)
    	{
    		got_SIGHUP = false;
    		ProcessConfigFile(PGC_SIGHUP);
    	}
    
    	/*
    	 * Check if we were requested to exit without finishing recovery.
    	 */
    	if (shutdown_requested)
    		proc_exit(1);
    
    	/*
    	 * Emergency bailout if postmaster has died.  This is to avoid the
    	 * necessity for manual cleanup of all postmaster children.
    	 */
    	if (IsUnderPostmaster && !PostmasterIsAlive(true))
    		exit(1);
    }
    
    /* Main entry point for startup process */
    void
    StartupProcessMain(void)
    {
    	/*
    	 * If possible, make this process a group leader, so that the postmaster
    	 * can signal any child processes too.
    	 */
    #ifdef HAVE_SETSID
    	if (setsid() < 0)
    		elog(FATAL, "setsid() failed: %m");
    #endif
    
    	/*
    	 * Properly accept or ignore signals the postmaster might send us
    	 */
    	pqsignal(SIGHUP, StartupProcSigHupHandler); /* reload config file */
    	pqsignal(SIGINT, SIG_IGN);	/* ignore query cancel */
    	pqsignal(SIGTERM, StartupProcShutdownHandler);		/* request shutdown */
    	pqsignal(SIGQUIT, startupproc_quickdie);	/* hard crash time */
    	if (XLogRequestRecoveryConnections)
    		pqsignal(SIGALRM, handle_standby_sig_alarm);	/* ignored unless
    														 * InHotStandby */
    	else
    		pqsignal(SIGALRM, SIG_IGN);
    	pqsignal(SIGPIPE, SIG_IGN);
    	pqsignal(SIGUSR1, SIG_IGN);
    	pqsignal(SIGUSR2, SIG_IGN);
    
    	/*
    	 * Reset some signals that are accepted by postmaster but not here
    	 */
    	pqsignal(SIGCHLD, SIG_DFL);
    	pqsignal(SIGTTIN, SIG_DFL);
    	pqsignal(SIGTTOU, SIG_DFL);
    	pqsignal(SIGCONT, SIG_DFL);
    	pqsignal(SIGWINCH, SIG_DFL);
    
    	/*
    	 * Unblock signals (they were blocked when the postmaster forked us)
    	 */
    	PG_SETMASK(&UnBlockSig);
    
    	StartupXLOG();
    
    	/*
    	 * Exit normally. Exit code 0 tells postmaster that we completed recovery
    	 * successfully.
    	 */
    	proc_exit(0);
    }
    
    /*
     * Read the XLOG page containing RecPtr into readBuf (if not read already).
     * Returns true if successful, false otherwise or fails if emode is PANIC.
     *
     * This is responsible for restoring files from archive as needed, as well
     * as for waiting for the requested WAL record to arrive in standby mode.
     */
    static bool
    XLogPageRead(XLogRecPtr *RecPtr, int emode, bool fetching_ckpt,
    			 bool randAccess)
    {
    	static XLogRecPtr receivedUpto = {0, 0};
    	bool		switched_segment = false;
    	uint32		targetPageOff;
    	uint32		targetRecOff;
    	uint32		targetId;
    	uint32		targetSeg;
    
    	XLByteToSeg(*RecPtr, targetId, targetSeg);
    	targetPageOff = ((RecPtr->xrecoff % XLogSegSize) / XLOG_BLCKSZ) * XLOG_BLCKSZ;
    	targetRecOff = RecPtr->xrecoff % XLOG_BLCKSZ;
    
    	/* Fast exit if we have read the record in the current buffer already */
    	if (targetId == readId && targetSeg == readSeg &&
    		targetPageOff == readOff && targetRecOff < readLen)
    		return true;
    
    	/*
    	 * See if we need to switch to a new segment because the requested record
    	 * is not in the currently open one.
    	 */
    	if (readFile >= 0 && !XLByteInSeg(*RecPtr, readId, readSeg))
    	{
    		close(readFile);
    		readFile = -1;
    	}
    
    	XLByteToSeg(*RecPtr, readId, readSeg);
    
    	/* See if we need to retrieve more data */
    	if (readFile < 0 ||
    		(readStreamed && !XLByteLT(*RecPtr, receivedUpto)))
    	{
    		if (StandbyMode)
    		{
    			bool		last_restore_failed = false;
    
    			/*
    			 * In standby mode, wait for the requested record to become
    			 * available, either via restore_command succeeding to restore the
    			 * segment, or via walreceiver having streamed the record.
    			 */
    			for (;;)
    			{
    				if (WalRcvInProgress())
    				{
    					/*
    					 * While walreceiver is active, wait for new WAL to arrive
    					 * from primary.
    					 */
    					receivedUpto = GetWalRcvWriteRecPtr();
    					if (XLByteLT(*RecPtr, receivedUpto))
    					{
    						/*
    						 * Great, streamed far enough. Open the file if it's
    						 * not open already.
    						 */
    						if (readFile < 0)
    						{
    							readFile =
    								XLogFileRead(readId, readSeg, PANIC,
    											 recoveryTargetTLI, false, false);
    							switched_segment = true;
    							readStreamed = true;
    						}
    						break;
    					}
    
    					if (CheckForStandbyTrigger())
    						goto next_record_is_invalid;
    
    					/*
    					 * When streaming is active, we want to react quickly when
    					 * the next WAL record arrives, so sleep only a bit.
    					 */
    					pg_usleep(100000L); /* 100ms */
    				}
    				else
    				{
    					/*
    					 * Until walreceiver manages to reconnect, poll the
    					 * archive.
    					 */
    					if (readFile >= 0)
    					{
    						close(readFile);
    						readFile = -1;
    					}
    					/* Reset curFileTLI if random fetch. */
    					if (randAccess)
    						curFileTLI = 0;
    					readFile = XLogFileReadAnyTLI(readId, readSeg, DEBUG2, true);
    					switched_segment = true;
    					readStreamed = false;
    					if (readFile != -1)
    					{
    						elog(DEBUG1, "got WAL segment from archive");
    						break;
    					}
    
    					/*
    					 * If we succeeded restoring some segments from archive
    					 * since the last connection attempt (or we haven't tried
    					 * streaming yet, retry immediately. But if we haven't,
    					 * assume the problem is persistent, so be less
    					 * aggressive.
    					 */
    					if (last_restore_failed)
    					{
    						/*
    						 * Check to see if the trigger file exists. Note that
    						 * we do this only after failure, so when you create
    						 * the trigger file, we still finish replaying as much
    						 * as we can before failover.
    						 */
    						if (CheckForStandbyTrigger())
    							goto next_record_is_invalid;
    						pg_usleep(5000000L);	/* 5 seconds */
    					}
    					last_restore_failed = true;
    
    					/*
    					 * Nope, not found in archive. Try to stream it.
    					 *
    					 * If fetching_ckpt is TRUE, RecPtr points to the initial
    					 * checkpoint location. In that case, we use RedoStartLSN
    					 * as the streaming start position instead of RecPtr, so
    					 * that when we later jump backwards to start redo at
    					 * RedoStartLSN, we will have the logs streamed already.
    					 */
    					if (PrimaryConnInfo)
    						RequestXLogStreaming(fetching_ckpt ? RedoStartLSN : *RecPtr,
    											 PrimaryConnInfo);
    				}
    
    				/*
    				 * This possibly-long loop needs to handle interrupts of
    				 * startup process.
    				 */
    				HandleStartupProcInterrupts();
    			}
    		}
    		else
    		{
    			/* In archive or crash recovery. */
    			if (readFile < 0)
    			{
    				/* Reset curFileTLI if random fetch. */
    				if (randAccess)
    					curFileTLI = 0;
    				readFile = XLogFileReadAnyTLI(readId, readSeg, emode,
    											  InArchiveRecovery);
    				switched_segment = true;
    				readStreamed = false;
    				if (readFile < 0)
    					return false;
    			}
    		}
    	}
    
    	/*
    	 * At this point, we have the right segment open and we know the requested
    	 * record is in it.
    	 */
    	Assert(readFile != -1);
    
    	/*
    	 * If the current segment is being streamed from master, calculate how
    	 * much of the current page we have received already. We know the
    	 * requested record has been received, but this is for the benefit of
    	 * future calls, to allow quick exit at the top of this function.
    	 */
    	if (readStreamed)
    	{
    		if (RecPtr->xlogid != receivedUpto.xlogid ||
    			(RecPtr->xrecoff / XLOG_BLCKSZ) != (receivedUpto.xrecoff / XLOG_BLCKSZ))
    		{
    			readLen = XLOG_BLCKSZ;
    		}
    		else
    			readLen = receivedUpto.xrecoff % XLogSegSize - targetPageOff;
    	}
    	else
    		readLen = XLOG_BLCKSZ;
    
    	if (switched_segment && targetPageOff != 0)
    	{
    		/*
    		 * Whenever switching to a new WAL segment, we read the first page of
    		 * the file and validate its header, even if that's not where the
    		 * target record is.  This is so that we can check the additional
    		 * identification info that is present in the first page's "long"
    		 * header.
    		 */
    		readOff = 0;
    		if (read(readFile, readBuf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
    		{
    			ereport(emode,
    					(errcode_for_file_access(),
    					 errmsg("could not read from log file %u, segment %u, offset %u: %m",
    							readId, readSeg, readOff)));
    			goto next_record_is_invalid;
    		}
    		if (!ValidXLOGHeader((XLogPageHeader) readBuf, emode))
    			goto next_record_is_invalid;
    	}
    
    	/* Read the requested page */
    	readOff = targetPageOff;
    	if (lseek(readFile, (off_t) readOff, SEEK_SET) < 0)
    	{
    		ereport(emode,
    				(errcode_for_file_access(),
    		 errmsg("could not seek in log file %u, segment %u to offset %u: %m",
    				readId, readSeg, readOff)));
    		goto next_record_is_invalid;
    	}
    	if (read(readFile, readBuf, XLOG_BLCKSZ) != XLOG_BLCKSZ)
    	{
    		ereport(emode,
    				(errcode_for_file_access(),
    		 errmsg("could not read from log file %u, segment %u, offset %u: %m",
    				readId, readSeg, readOff)));
    		goto next_record_is_invalid;
    	}
    	if (!ValidXLOGHeader((XLogPageHeader) readBuf, emode))
    		goto next_record_is_invalid;
    
    	Assert(targetId == readId);
    	Assert(targetSeg == readSeg);
    	Assert(targetPageOff == readOff);
    	Assert(targetRecOff < readLen);
    
    	return true;
    
    next_record_is_invalid:
    	if (readFile >= 0)
    		close(readFile);
    	readFile = -1;
    	readStreamed = false;
    	readLen = 0;
    
    	return false;
    }
    
    /*
     * Check to see if the trigger file exists. If it does, request postmaster
     * to shut down walreceiver, wait for it to exit, remove the trigger
     * file, and return true.
     */
    static bool
    CheckForStandbyTrigger(void)
    {
    	struct stat stat_buf;
    
    	if (TriggerFile == NULL)
    		return false;
    
    	if (stat(TriggerFile, &stat_buf) == 0)
    	{
    		ereport(LOG,
    				(errmsg("trigger file found: %s", TriggerFile)));
    		ShutdownWalRcv();
    		unlink(TriggerFile);
    		return true;
    	}
    	return false;
    }