diff --git a/src/backend/storage/ipc/shmem.c b/src/backend/storage/ipc/shmem.c
index 3bce41d4abbc25134879577687d9399e49a1e5da..6a65429f0fcc24804c168a143d5b671f0df8a760 100644
--- a/src/backend/storage/ipc/shmem.c
+++ b/src/backend/storage/ipc/shmem.c
@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/storage/ipc/shmem.c,v 1.93 2006/07/14 14:52:22 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/storage/ipc/shmem.c,v 1.94 2006/07/22 23:04:39 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -211,9 +211,6 @@ InitShmemIndex(void)
{
HASHCTL info;
int hash_flags;
- ShmemIndexEnt *result,
- item;
- bool found;
/*
* Since ShmemInitHash calls ShmemInitStruct, which expects the ShmemIndex
@@ -227,32 +224,11 @@ InitShmemIndex(void)
info.entrysize = sizeof(ShmemIndexEnt);
hash_flags = HASH_ELEM;
- /* This will acquire the shmem index lock, but not release it. */
ShmemIndex = ShmemInitHash("ShmemIndex",
SHMEM_INDEX_SIZE, SHMEM_INDEX_SIZE,
&info, hash_flags);
if (!ShmemIndex)
elog(FATAL, "could not initialize Shmem Index");
-
- /*
- * Now, create an entry in the hashtable for the index itself.
- */
- if (!IsUnderPostmaster)
- {
- MemSet(item.key, 0, SHMEM_INDEX_KEYSIZE);
- strncpy(item.key, "ShmemIndex", SHMEM_INDEX_KEYSIZE);
-
- result = (ShmemIndexEnt *)
- hash_search(ShmemIndex, (void *) &item, HASH_ENTER, &found);
-
- Assert(!found);
-
- result->location = MAKE_OFFSET(ShmemIndex->hctl);
- result->size = SHMEM_INDEX_SIZE;
- }
-
- /* now release the lock acquired in ShmemInitStruct */
- LWLockRelease(ShmemIndexLock);
}
/*
@@ -295,7 +271,7 @@ ShmemInitHash(const char *name, /* table string name for shmem index */
/* look it up in the shmem index */
location = ShmemInitStruct(name,
- sizeof(HASHHDR) + infoP->dsize * sizeof(HASHSEGMENT),
+ hash_get_shared_size(infoP, hash_flags),
&found);
/*
@@ -312,9 +288,8 @@ ShmemInitHash(const char *name, /* table string name for shmem index */
if (found)
hash_flags |= HASH_ATTACH;
- /* Now provide the header and directory pointers */
+ /* Pass location of hashtable header to hash_create */
infoP->hctl = (HASHHDR *) location;
- infoP->dir = (HASHSEGMENT *) (((char *) location) + sizeof(HASHHDR));
return hash_create(name, init_size, infoP, hash_flags);
}
@@ -363,14 +338,16 @@ ShmemInitStruct(const char *name, Size size, bool *foundPtr)
* If the shmem index doesn't exist, we are bootstrapping: we must
* be trying to init the shmem index itself.
*
- * Notice that the ShmemIndexLock is held until the shmem index
- * has been completely initialized.
+ * Notice that the ShmemIndexLock is released before the shmem
+ * index has been initialized. This should be OK because no
+ * other process can be accessing shared memory yet.
*/
Assert(shmemseghdr->indexoffset == 0);
structPtr = ShmemAlloc(size);
shmemseghdr->indexoffset = MAKE_OFFSET(structPtr);
*foundPtr = FALSE;
}
+ LWLockRelease(ShmemIndexLock);
return structPtr;
}
diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c
index 472b3d1f4b3de282a457afa0cfaed323c4b5b3fb..cf78869a0b2d12d30ee3a42ca632c7143380a594 100644
--- a/src/backend/storage/lmgr/lock.c
+++ b/src/backend/storage/lmgr/lock.c
@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/storage/lmgr/lock.c,v 1.166 2006/07/14 14:52:23 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/storage/lmgr/lock.c,v 1.167 2006/07/22 23:04:39 tgl Exp $
*
* NOTES
* A lock table is a shared memory hash table. When
@@ -1958,7 +1958,7 @@ GetLockStatusData(void)
{
LWLockAcquire(FirstLockMgrLock + i, LW_SHARED);
proclockTable = LockMethodProcLockHash[i];
- els += proclockTable->hctl->nentries;
+ els += hash_get_num_entries(proclockTable);
}
data->nelements = els;
diff --git a/src/backend/utils/hash/dynahash.c b/src/backend/utils/hash/dynahash.c
index f98b94942315c902bb3b5dced47903b9eed9843e..23200667afd5de07326803781c249ada240e7b02 100644
--- a/src/backend/utils/hash/dynahash.c
+++ b/src/backend/utils/hash/dynahash.c
@@ -3,17 +3,36 @@
* dynahash.c
* dynamic hash tables
*
+ * dynahash.c supports both local-to-a-backend hash tables and hash tables in
+ * shared memory. For shared hash tables, it is the caller's responsibility
+ * to provide appropriate access interlocking. The simplest convention is
+ * that a single LWLock protects the whole hash table. Searches (HASH_FIND or
+ * hash_seq_search) need only shared lock, but any update requires exclusive
+ * lock. For heavily-used shared tables, the single-lock approach creates a
+ * concurrency bottleneck, so we also support "partitioned" locking wherein
+ * there are multiple LWLocks guarding distinct subsets of the table. To use
+ * a hash table in partitioned mode, the HASH_PARTITION flag must be given
+ * to hash_create. This prevents any attempt to split buckets on-the-fly.
+ * Therefore, each hash bucket chain operates independently, and no fields
+ * of the hash header change after init except nentries and freeList.
+ * A partitioned table uses a spinlock to guard changes of those two fields.
+ * This lets any subset of the hash buckets be treated as a separately
+ * lockable partition. We expect callers to use the low-order bits of a
+ * lookup key's hash value as a partition number --- this will work because
+ * of the way calc_bucket() maps hash values to bucket numbers.
*
* Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/utils/hash/dynahash.c,v 1.69 2006/07/14 14:52:25 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/utils/hash/dynahash.c,v 1.70 2006/07/22 23:04:39 tgl Exp $
*
*-------------------------------------------------------------------------
*/
+
/*
+ * Original comments:
*
* Dynamic hashing, after CACM April 1988 pp 446-457, by Per-Ake Larson.
* Coded into C, with minor code improvements, and with hsearch(3) interface,
@@ -45,9 +64,107 @@
#include "postgres.h"
#include "storage/shmem.h"
+#include "storage/spin.h"
#include "utils/dynahash.h"
#include "utils/memutils.h"
+
+/*
+ * Constants
+ *
+ * A hash table has a top-level "directory", each of whose entries points
+ * to a "segment" of ssize bucket headers. The maximum number of hash
+ * buckets is thus dsize * ssize (but dsize may be expansible). Of course,
+ * the number of records in the table can be larger, but we don't want a
+ * whole lot of records per bucket or performance goes down.
+ *
+ * In a hash table allocated in shared memory, the directory cannot be
+ * expanded because it must stay at a fixed address. The directory size
+ * should be selected using hash_select_dirsize (and you'd better have
+ * a good idea of the maximum number of entries!). For non-shared hash
+ * tables, the initial directory size can be left at the default.
+ */
+#define DEF_SEGSIZE 256
+#define DEF_SEGSIZE_SHIFT 8 /* must be log2(DEF_SEGSIZE) */
+#define DEF_DIRSIZE 256
+#define DEF_FFACTOR 1 /* default fill factor */
+
+
+/* A hash bucket is a linked list of HASHELEMENTs */
+typedef HASHELEMENT *HASHBUCKET;
+
+/* A hash segment is an array of bucket headers */
+typedef HASHBUCKET *HASHSEGMENT;
+
+/*
+ * Header structure for a hash table --- contains all changeable info
+ *
+ * In a shared-memory hash table, the HASHHDR is in shared memory, while
+ * each backend has a local HTAB struct. For a non-shared table, there isn't
+ * any functional difference between HASHHDR and HTAB, but we separate them
+ * anyway to share code between shared and non-shared tables.
+ */
+struct HASHHDR
+{
+ /* In a partitioned table, take this lock to touch nentries or freeList */
+ slock_t mutex; /* unused if not partitioned table */
+
+ /* These fields change during entry addition/deletion */
+ long nentries; /* number of entries in hash table */
+ HASHELEMENT *freeList; /* linked list of free elements */
+
+ /* These fields can change, but not in a partitioned table */
+ /* Also, dsize can't change in a shared table, even if unpartitioned */
+ long dsize; /* directory size */
+ long nsegs; /* number of allocated segments (<= dsize) */
+ uint32 max_bucket; /* ID of maximum bucket in use */
+ uint32 high_mask; /* mask to modulo into entire table */
+ uint32 low_mask; /* mask to modulo into lower half of table */
+
+ /* These fields are fixed at hashtable creation */
+ Size keysize; /* hash key length in bytes */
+ Size entrysize; /* total user element size in bytes */
+ long num_partitions; /* # partitions (must be power of 2), or 0 */
+ long ffactor; /* target fill factor */
+ long max_dsize; /* 'dsize' limit if directory is fixed size */
+ long ssize; /* segment size --- must be power of 2 */
+ int sshift; /* segment shift = log2(ssize) */
+ int nelem_alloc; /* number of entries to allocate at once */
+
+#ifdef HASH_STATISTICS
+ /*
+ * Count statistics here. NB: stats code doesn't bother with mutex,
+ * so counts could be corrupted a bit in a partitioned table.
+ */
+ long accesses;
+ long collisions;
+#endif
+};
+
+#define IS_PARTITIONED(hctl) ((hctl)->num_partitions != 0)
+
+/*
+ * Top control structure for a hashtable --- in a shared table, each backend
+ * has its own copy (OK since no fields change at runtime)
+ */
+struct HTAB
+{
+ HASHHDR *hctl; /* => shared control information */
+ HASHSEGMENT *dir; /* directory of segment starts */
+ HashValueFunc hash; /* hash function */
+ HashCompareFunc match; /* key comparison function */
+ HashCopyFunc keycopy; /* key copying function */
+ HashAllocFunc alloc; /* memory allocator */
+ MemoryContext hcxt; /* memory context if default allocator used */
+ char *tabname; /* table name (for error messages) */
+ bool isshared; /* true if table is in shared memory */
+
+ /* We keep local copies of these fixed values to reduce contention */
+ Size keysize; /* hash key length in bytes */
+ long ssize; /* segment size --- must be power of 2 */
+ int sshift; /* segment shift = log2(ssize) */
+};
+
/*
* Key (also entry) part of a HASHELEMENT
*/
@@ -58,6 +175,12 @@
*/
#define MOD(x,y) ((x) & ((y)-1))
+#if HASH_STATISTICS
+static long hash_accesses,
+ hash_collisions,
+ hash_expansions;
+#endif
+
/*
* Private function prototypes
*/
@@ -66,6 +189,7 @@ static HASHSEGMENT seg_alloc(HTAB *hashp);
static bool element_alloc(HTAB *hashp, int nelem);
static bool dir_realloc(HTAB *hashp);
static bool expand_table(HTAB *hashp);
+static HASHBUCKET get_hash_entry(HTAB *hashp);
static void hdefault(HTAB *hashp);
static int choose_nelem_alloc(Size entrysize);
static bool init_htab(HTAB *hashp, long nelem);
@@ -85,13 +209,6 @@ DynaHashAlloc(Size size)
}
-#if HASH_STATISTICS
-static long hash_accesses,
- hash_collisions,
- hash_expansions;
-#endif
-
-
/************************** CREATE ROUTINES **********************/
/*
@@ -185,17 +302,26 @@ hash_create(const char *tabname, long nelem, HASHCTL *info, int flags)
if (flags & HASH_SHARED_MEM)
{
/*
- * ctl structure is preallocated for shared memory tables. Note that
- * HASH_DIRSIZE and HASH_ALLOC had better be set as well.
+ * ctl structure and directory are preallocated for shared memory
+ * tables. Note that HASH_DIRSIZE and HASH_ALLOC had better be set
+ * as well.
*/
hashp->hctl = info->hctl;
- hashp->dir = info->dir;
+ hashp->dir = (HASHSEGMENT *) (((char *) info->hctl) + sizeof(HASHHDR));
hashp->hcxt = NULL;
hashp->isshared = true;
/* hash table already exists, we're just attaching to it */
if (flags & HASH_ATTACH)
+ {
+ /* make local copies of some heavily-used values */
+ hctl = hashp->hctl;
+ hashp->keysize = hctl->keysize;
+ hashp->ssize = hctl->ssize;
+ hashp->sshift = hctl->sshift;
+
return hashp;
+ }
}
else
{
@@ -218,9 +344,16 @@ hash_create(const char *tabname, long nelem, HASHCTL *info, int flags)
hdefault(hashp);
hctl = hashp->hctl;
-#ifdef HASH_STATISTICS
- hctl->accesses = hctl->collisions = 0;
-#endif
+
+ if (flags & HASH_PARTITION)
+ {
+ /* Doesn't make sense to partition a local hash table */
+ Assert(flags & HASH_SHARED_MEM);
+ /* # of partitions had better be a power of 2 */
+ Assert(info->num_partitions == (1L << my_log2(info->num_partitions)));
+
+ hctl->num_partitions = info->num_partitions;
+ }
if (flags & HASH_SEGMENT)
{
@@ -252,6 +385,11 @@ hash_create(const char *tabname, long nelem, HASHCTL *info, int flags)
hctl->entrysize = info->entrysize;
}
+ /* make local copies of heavily-used constant fields */
+ hashp->keysize = hctl->keysize;
+ hashp->ssize = hctl->ssize;
+ hashp->sshift = hctl->sshift;
+
/* Build the hash directory structure */
if (!init_htab(hashp, nelem))
{
@@ -292,22 +430,29 @@ hdefault(HTAB *hashp)
MemSet(hctl, 0, sizeof(HASHHDR));
- hctl->ssize = DEF_SEGSIZE;
- hctl->sshift = DEF_SEGSIZE_SHIFT;
- hctl->dsize = DEF_DIRSIZE;
- hctl->ffactor = DEF_FFACTOR;
hctl->nentries = 0;
+ hctl->freeList = NULL;
+
+ hctl->dsize = DEF_DIRSIZE;
hctl->nsegs = 0;
/* rather pointless defaults for key & entry size */
hctl->keysize = sizeof(char *);
hctl->entrysize = 2 * sizeof(char *);
+ hctl->num_partitions = 0; /* not partitioned */
+
+ hctl->ffactor = DEF_FFACTOR;
+
/* table has no fixed maximum size */
hctl->max_dsize = NO_MAX_DSIZE;
- /* garbage collection for HASH_REMOVE */
- hctl->freeList = NULL;
+ hctl->ssize = DEF_SEGSIZE;
+ hctl->sshift = DEF_SEGSIZE_SHIFT;
+
+#ifdef HASH_STATISTICS
+ hctl->accesses = hctl->collisions = 0;
+#endif
}
/*
@@ -342,6 +487,10 @@ choose_nelem_alloc(Size entrysize)
return nelem_alloc;
}
+/*
+ * Compute derived fields of hctl and build the initial directory/segment
+ * arrays
+ */
static bool
init_htab(HTAB *hashp, long nelem)
{
@@ -351,6 +500,12 @@ init_htab(HTAB *hashp, long nelem)
int nbuckets;
int nsegs;
+ /*
+ * initialize mutex if it's a partitioned table
+ */
+ if (IS_PARTITIONED(hctl))
+ SpinLockInit(&hctl->mutex);
+
/*
* Divide number of elements by the fill factor to determine a desired
* number of buckets. Allocate space for the next greater power of two
@@ -360,6 +515,15 @@ init_htab(HTAB *hashp, long nelem)
nbuckets = 1 << my_log2(lnbuckets);
+ /*
+ * In a partitioned table, nbuckets must be at least equal to
+ * num_partitions; were it less, keys with apparently different partition
+ * numbers would map to the same bucket, breaking partition independence.
+ * (Normally nbuckets will be much bigger; this is just a safety check.)
+ */
+ while (nbuckets < hctl->num_partitions)
+ nbuckets <<= 1;
+
hctl->max_bucket = hctl->low_mask = nbuckets - 1;
hctl->high_mask = (nbuckets << 1) - 1;
@@ -491,6 +655,19 @@ hash_select_dirsize(long num_entries)
return nDirEntries;
}
+/*
+ * Compute the required initial memory allocation for a shared-memory
+ * hashtable with the given parameters. We need space for the HASHHDR
+ * and for the (non expansible) directory.
+ */
+Size
+hash_get_shared_size(HASHCTL *info, int flags)
+{
+ Assert(flags & HASH_DIRSIZE);
+ Assert(info->dsize == info->max_dsize);
+ return sizeof(HASHHDR) + info->dsize * sizeof(HASHSEGMENT);
+}
+
/********************** DESTROY ROUTINES ************************/
@@ -521,7 +698,7 @@ hash_stats(const char *where, HTAB *hashp)
where, hashp->hctl->accesses, hashp->hctl->collisions);
fprintf(stderr, "hash_stats: entries %ld keysize %ld maxp %u segmentcount %ld\n",
- hashp->hctl->nentries, hashp->hctl->keysize,
+ hashp->hctl->nentries, (long) hashp->hctl->keysize,
hashp->hctl->max_bucket, hashp->hctl->nsegs);
fprintf(stderr, "%s: total accesses %ld total collisions %ld\n",
where, hash_accesses, hash_collisions);
@@ -533,6 +710,19 @@ hash_stats(const char *where, HTAB *hashp)
/*******************************SEARCH ROUTINES *****************************/
+/*
+ * get_hash_value -- exported routine to calculate a key's hash value
+ *
+ * We export this because for partitioned tables, callers need to compute
+ * the partition number (from the low-order bits of the hash value) before
+ * searching.
+ */
+uint32
+get_hash_value(HTAB *hashp, const void *keyPtr)
+{
+ return hashp->hash(keyPtr, hashp->keysize);
+}
+
/* Convert a hash value to a bucket number */
static inline uint32
calc_bucket(HASHHDR *hctl, uint32 hash_val)
@@ -546,8 +736,9 @@ calc_bucket(HASHHDR *hctl, uint32 hash_val)
return bucket;
}
-/*----------
+/*
* hash_search -- look up key in table and perform action
+ * hash_search_with_hash_value -- same, with key's hash value already computed
*
* action is one of:
* HASH_FIND: look up key in table
@@ -568,17 +759,32 @@ calc_bucket(HASHHDR *hctl, uint32 hash_val)
* If foundPtr isn't NULL, then *foundPtr is set TRUE if we found an
* existing entry in the table, FALSE otherwise. This is needed in the
* HASH_ENTER case, but is redundant with the return value otherwise.
- *----------
+ *
+ * For hash_search_with_hash_value, the hashvalue parameter must have been
+ * calculated with get_hash_value().
*/
void *
hash_search(HTAB *hashp,
const void *keyPtr,
HASHACTION action,
bool *foundPtr)
+{
+ return hash_search_with_hash_value(hashp,
+ keyPtr,
+ hashp->hash(keyPtr, hashp->keysize),
+ action,
+ foundPtr);
+}
+
+void *
+hash_search_with_hash_value(HTAB *hashp,
+ const void *keyPtr,
+ uint32 hashvalue,
+ HASHACTION action,
+ bool *foundPtr)
{
HASHHDR *hctl = hashp->hctl;
- Size keysize = hctl->keysize;
- uint32 hashvalue;
+ Size keysize;
uint32 bucket;
long segment_num;
long segment_ndx;
@@ -595,11 +801,10 @@ hash_search(HTAB *hashp,
/*
* Do the initial lookup
*/
- hashvalue = hashp->hash(keyPtr, keysize);
bucket = calc_bucket(hctl, hashvalue);
- segment_num = bucket >> hctl->sshift;
- segment_ndx = MOD(bucket, hctl->ssize);
+ segment_num = bucket >> hashp->sshift;
+ segment_ndx = MOD(bucket, hashp->ssize);
segp = hashp->dir[segment_num];
@@ -613,6 +818,7 @@ hash_search(HTAB *hashp,
* Follow collision chain looking for matching key
*/
match = hashp->match; /* save one fetch in inner loop */
+ keysize = hashp->keysize; /* ditto */
while (currBucket != NULL)
{
@@ -643,15 +849,25 @@ hash_search(HTAB *hashp,
case HASH_REMOVE:
if (currBucket != NULL)
{
- Assert(hctl->nentries > 0);
- hctl->nentries--;
+ /* use volatile pointer to prevent code rearrangement */
+ volatile HASHHDR *hctlv = hctl;
+
+ /* if partitioned, must lock to touch nentries and freeList */
+ if (IS_PARTITIONED(hctlv))
+ SpinLockAcquire(&hctlv->mutex);
+
+ Assert(hctlv->nentries > 0);
+ hctlv->nentries--;
/* remove record from hash bucket's chain. */
*prevBucketPtr = currBucket->link;
/* add the record to the freelist for this table. */
- currBucket->link = hctl->freeList;
- hctl->freeList = currBucket;
+ currBucket->link = hctlv->freeList;
+ hctlv->freeList = currBucket;
+
+ if (IS_PARTITIONED(hctlv))
+ SpinLockRelease(&hctlv->mutex);
/*
* better hope the caller is synchronizing access to this
@@ -672,32 +888,23 @@ hash_search(HTAB *hashp,
if (currBucket != NULL)
return (void *) ELEMENTKEY(currBucket);
- /* get the next free element */
- currBucket = hctl->freeList;
+ currBucket = get_hash_entry(hashp);
if (currBucket == NULL)
{
- /* no free elements. allocate another chunk of buckets */
- if (!element_alloc(hashp, hctl->nelem_alloc))
- {
- /* out of memory */
- if (action == HASH_ENTER_NULL)
- return NULL;
- /* report a generic message */
- if (hashp->isshared)
- ereport(ERROR,
- (errcode(ERRCODE_OUT_OF_MEMORY),
- errmsg("out of shared memory")));
- else
- ereport(ERROR,
- (errcode(ERRCODE_OUT_OF_MEMORY),
- errmsg("out of memory")));
- }
- currBucket = hctl->freeList;
- Assert(currBucket != NULL);
+ /* out of memory */
+ if (action == HASH_ENTER_NULL)
+ return NULL;
+ /* report a generic message */
+ if (hashp->isshared)
+ ereport(ERROR,
+ (errcode(ERRCODE_OUT_OF_MEMORY),
+ errmsg("out of shared memory")));
+ else
+ ereport(ERROR,
+ (errcode(ERRCODE_OUT_OF_MEMORY),
+ errmsg("out of memory")));
}
- hctl->freeList = currBucket->link;
-
/* link into hashbucket chain */
*prevBucketPtr = currBucket;
currBucket->link = NULL;
@@ -708,8 +915,10 @@ hash_search(HTAB *hashp,
/* caller is expected to fill the data field on return */
- /* Check if it is time to split the segment */
- if (++hctl->nentries / (long) (hctl->max_bucket + 1) >= hctl->ffactor)
+ /* Check if it is time to split a bucket */
+ /* Can't split if running in partitioned mode */
+ if (!IS_PARTITIONED(hctl) &&
+ hctl->nentries / (long) (hctl->max_bucket + 1) >= hctl->ffactor)
{
/*
* NOTE: failure to expand table is not a fatal error, it just
@@ -726,6 +935,61 @@ hash_search(HTAB *hashp,
return NULL; /* keep compiler quiet */
}
+/*
+ * create a new entry if possible
+ */
+static HASHBUCKET
+get_hash_entry(HTAB *hashp)
+{
+ /* use volatile pointer to prevent code rearrangement */
+ volatile HASHHDR *hctlv = hashp->hctl;
+ HASHBUCKET newElement;
+
+ for (;;)
+ {
+ /* if partitioned, must lock to touch nentries and freeList */
+ if (IS_PARTITIONED(hctlv))
+ SpinLockAcquire(&hctlv->mutex);
+
+ /* try to get an entry from the freelist */
+ newElement = hctlv->freeList;
+ if (newElement != NULL)
+ break;
+
+ /* no free elements. allocate another chunk of buckets */
+ if (IS_PARTITIONED(hctlv))
+ SpinLockRelease(&hctlv->mutex);
+
+ if (!element_alloc(hashp, hctlv->nelem_alloc))
+ {
+ /* out of memory */
+ return NULL;
+ }
+ }
+
+ /* remove entry from freelist, bump nentries */
+ hctlv->freeList = newElement->link;
+ hctlv->nentries++;
+
+ if (IS_PARTITIONED(hctlv))
+ SpinLockRelease(&hctlv->mutex);
+
+ return newElement;
+}
+
+/*
+ * hash_get_num_entries -- get the number of entries in a hashtable
+ */
+long
+hash_get_num_entries(HTAB *hashp)
+{
+ /*
+ * We currently don't bother with the mutex; it's only sensible to call
+ * this function if you've got lock on all partitions of the table.
+ */
+ return hashp->hctl->nentries;
+}
+
/*
* hash_seq_init/_search
* Sequentially search through hash table and return
@@ -736,6 +1000,9 @@ hash_search(HTAB *hashp,
* UNDEFINED (it might be the one that curIndex is pointing at!). Also,
* if elements are added to the table while the scan is in progress, it is
* unspecified whether they will be visited by the scan or not.
+ *
+ * NOTE: to use this with a partitioned hashtable, caller had better hold
+ * at least shared lock on all partitions of the table throughout the scan!
*/
void
hash_seq_init(HASH_SEQ_STATUS *status, HTAB *hashp)
@@ -773,7 +1040,7 @@ hash_seq_search(HASH_SEQ_STATUS *status)
curBucket = status->curBucket;
hashp = status->hashp;
hctl = hashp->hctl;
- ssize = hctl->ssize;
+ ssize = hashp->ssize;
max_bucket = hctl->max_bucket;
if (curBucket > max_bucket)
@@ -782,7 +1049,7 @@ hash_seq_search(HASH_SEQ_STATUS *status)
/*
* first find the right segment in the table directory.
*/
- segment_num = curBucket >> hctl->sshift;
+ segment_num = curBucket >> hashp->sshift;
segment_ndx = MOD(curBucket, ssize);
segp = hashp->dir[segment_num];
@@ -840,13 +1107,15 @@ expand_table(HTAB *hashp)
HASHBUCKET currElement,
nextElement;
+ Assert(!IS_PARTITIONED(hctl));
+
#ifdef HASH_STATISTICS
hash_expansions++;
#endif
new_bucket = hctl->max_bucket + 1;
- new_segnum = new_bucket >> hctl->sshift;
- new_segndx = MOD(new_bucket, hctl->ssize);
+ new_segnum = new_bucket >> hashp->sshift;
+ new_segndx = MOD(new_bucket, hashp->ssize);
if (new_segnum >= hctl->nsegs)
{
@@ -885,8 +1154,8 @@ expand_table(HTAB *hashp)
* split at this point. With a different way of reducing the hash value,
* that might not be true!
*/
- old_segnum = old_bucket >> hctl->sshift;
- old_segndx = MOD(old_bucket, hctl->ssize);
+ old_segnum = old_bucket >> hashp->sshift;
+ old_segndx = MOD(old_bucket, hashp->ssize);
old_seg = hashp->dir[old_segnum];
new_seg = hashp->dir[new_segnum];
@@ -963,12 +1232,12 @@ seg_alloc(HTAB *hashp)
HASHSEGMENT segp;
CurrentDynaHashCxt = hashp->hcxt;
- segp = (HASHSEGMENT) hashp->alloc(sizeof(HASHBUCKET) * hashp->hctl->ssize);
+ segp = (HASHSEGMENT) hashp->alloc(sizeof(HASHBUCKET) * hashp->ssize);
if (!segp)
return NULL;
- MemSet(segp, 0, sizeof(HASHBUCKET) * hashp->hctl->ssize);
+ MemSet(segp, 0, sizeof(HASHBUCKET) * hashp->ssize);
return segp;
}
@@ -979,29 +1248,44 @@ seg_alloc(HTAB *hashp)
static bool
element_alloc(HTAB *hashp, int nelem)
{
- HASHHDR *hctl = hashp->hctl;
+ /* use volatile pointer to prevent code rearrangement */
+ volatile HASHHDR *hctlv = hashp->hctl;
Size elementSize;
+ HASHELEMENT *firstElement;
HASHELEMENT *tmpElement;
+ HASHELEMENT *prevElement;
int i;
/* Each element has a HASHELEMENT header plus user data. */
- elementSize = MAXALIGN(sizeof(HASHELEMENT)) + MAXALIGN(hctl->entrysize);
+ elementSize = MAXALIGN(sizeof(HASHELEMENT)) + MAXALIGN(hctlv->entrysize);
CurrentDynaHashCxt = hashp->hcxt;
- tmpElement = (HASHELEMENT *)
- hashp->alloc(nelem * elementSize);
+ firstElement = (HASHELEMENT *) hashp->alloc(nelem * elementSize);
- if (!tmpElement)
+ if (!firstElement)
return false;
- /* link all the new entries into the freelist */
+ /* prepare to link all the new entries into the freelist */
+ prevElement = NULL;
+ tmpElement = firstElement;
for (i = 0; i < nelem; i++)
{
- tmpElement->link = hctl->freeList;
- hctl->freeList = tmpElement;
+ tmpElement->link = prevElement;
+ prevElement = tmpElement;
tmpElement = (HASHELEMENT *) (((char *) tmpElement) + elementSize);
}
+ /* if partitioned, must lock to touch freeList */
+ if (IS_PARTITIONED(hctlv))
+ SpinLockAcquire(&hctlv->mutex);
+
+ /* freelist could be nonempty if two backends did this concurrently */
+ firstElement->link = hctlv->freeList;
+ hctlv->freeList = prevElement;
+
+ if (IS_PARTITIONED(hctlv))
+ SpinLockRelease(&hctlv->mutex);
+
return true;
}
diff --git a/src/include/utils/hsearch.h b/src/include/utils/hsearch.h
index a89be514d90b9168a9804dfa9d3598caa33ef3e7..c682cf032959de84b397dc6810c33b72a2a2c3fa 100644
--- a/src/include/utils/hsearch.h
+++ b/src/include/utils/hsearch.h
@@ -1,13 +1,13 @@
/*-------------------------------------------------------------------------
*
* hsearch.h
- * for hash tables, particularly hash tables in shared memory
+ * exported definitions for utils/hash/dynahash.c; see notes therein
*
*
* Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
- * $PostgreSQL: pgsql/src/include/utils/hsearch.h,v 1.43 2006/06/25 18:29:49 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/utils/hsearch.h,v 1.44 2006/07/22 23:04:39 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -43,27 +43,6 @@ typedef void *(*HashCopyFunc) (void *dest, const void *src, Size keysize);
*/
typedef void *(*HashAllocFunc) (Size request);
-/*
- * Constants
- *
- * A hash table has a top-level "directory", each of whose entries points
- * to a "segment" of ssize bucket headers. The maximum number of hash
- * buckets is thus dsize * ssize (but dsize may be expansible). Of course,
- * the number of records in the table can be larger, but we don't want a
- * whole lot of records per bucket or performance goes down.
- *
- * In a hash table allocated in shared memory, the directory cannot be
- * expanded because it must stay at a fixed address. The directory size
- * should be selected using hash_select_dirsize (and you'd better have
- * a good idea of the maximum number of entries!). For non-shared hash
- * tables, the initial directory size can be left at the default.
- */
-#define DEF_SEGSIZE 256
-#define DEF_SEGSIZE_SHIFT 8 /* must be log2(DEF_SEGSIZE) */
-#define DEF_DIRSIZE 256
-#define DEF_FFACTOR 1 /* default fill factor */
-
-
/*
* HASHELEMENT is the private part of a hashtable entry. The caller's data
* follows the HASHELEMENT structure (on a MAXALIGN'd boundary). The hash key
@@ -75,81 +54,42 @@ typedef struct HASHELEMENT
uint32 hashvalue; /* hash function result for this entry */
} HASHELEMENT;
-/* A hash bucket is a linked list of HASHELEMENTs */
-typedef HASHELEMENT *HASHBUCKET;
+/* Hash table header struct is an opaque type known only within dynahash.c */
+typedef struct HASHHDR HASHHDR;
-/* A hash segment is an array of bucket headers */
-typedef HASHBUCKET *HASHSEGMENT;
-
-/* Header structure for a hash table --- contains all changeable info */
-typedef struct HASHHDR
-{
- long dsize; /* Directory Size */
- long ssize; /* Segment Size --- must be power of 2 */
- int sshift; /* Segment shift = log2(ssize) */
- uint32 max_bucket; /* ID of Maximum bucket in use */
- uint32 high_mask; /* Mask to modulo into entire table */
- uint32 low_mask; /* Mask to modulo into lower half of table */
- long ffactor; /* Fill factor */
- long nentries; /* Number of entries in hash table */
- long nsegs; /* Number of allocated segments */
- Size keysize; /* hash key length in bytes */
- Size entrysize; /* total user element size in bytes */
- long max_dsize; /* 'dsize' limit if directory is fixed size */
- int nelem_alloc; /* number of entries to allocate at once */
- HASHELEMENT *freeList; /* linked list of free elements */
-#ifdef HASH_STATISTICS
- long accesses;
- long collisions;
-#endif
-} HASHHDR;
-
-/*
- * Top control structure for a hashtable --- need not be shared, since
- * no fields change at runtime
- */
-typedef struct HTAB
-{
- HASHHDR *hctl; /* shared control information */
- HASHSEGMENT *dir; /* directory of segment starts */
- HashValueFunc hash; /* hash function */
- HashCompareFunc match; /* key comparison function */
- HashCopyFunc keycopy; /* key copying function */
- HashAllocFunc alloc; /* memory allocator */
- MemoryContext hcxt; /* memory context if default allocator used */
- char *tabname; /* table name (for error messages) */
- bool isshared; /* true if table is in shared memory */
-} HTAB;
+/* Hash table control struct is an opaque type known only within dynahash.c */
+typedef struct HTAB HTAB;
/* Parameter data structure for hash_create */
/* Only those fields indicated by hash_flags need be set */
typedef struct HASHCTL
{
- long ssize; /* Segment Size */
- long dsize; /* (initial) Directory Size */
- long max_dsize; /* limit to dsize if directory size is limited */
- long ffactor; /* Fill factor */
+ long num_partitions; /* # partitions (must be power of 2) */
+ long ssize; /* segment size */
+ long dsize; /* (initial) directory size */
+ long max_dsize; /* limit to dsize if dir size is limited */
+ long ffactor; /* fill factor */
Size keysize; /* hash key length in bytes */
Size entrysize; /* total user element size in bytes */
HashValueFunc hash; /* hash function */
HashCompareFunc match; /* key comparison function */
HashCopyFunc keycopy; /* key copying function */
HashAllocFunc alloc; /* memory allocator */
- HASHSEGMENT *dir; /* directory of segment starts */
- HASHHDR *hctl; /* location of header in shared mem */
MemoryContext hcxt; /* memory context to use for allocations */
+ HASHHDR *hctl; /* location of header in shared mem */
} HASHCTL;
/* Flags to indicate which parameters are supplied */
+#define HASH_PARTITION 0x001 /* Hashtable is used w/partitioned locking */
#define HASH_SEGMENT 0x002 /* Set segment size */
-#define HASH_DIRSIZE 0x004 /* Set directory size */
+#define HASH_DIRSIZE 0x004 /* Set directory size (initial and max) */
#define HASH_FFACTOR 0x008 /* Set fill factor */
#define HASH_FUNCTION 0x010 /* Set user defined hash function */
-#define HASH_ELEM 0x020 /* Set key/entry size */
+#define HASH_ELEM 0x020 /* Set keysize and entrysize */
#define HASH_SHARED_MEM 0x040 /* Hashtable is in shared memory */
#define HASH_ATTACH 0x080 /* Do not initialize hctl */
#define HASH_ALLOC 0x100 /* Set memory allocator */
-#define HASH_CONTEXT 0x200 /* Set explicit memory context */
+#define HASH_CONTEXT 0x200 /* Set memory allocation context */
#define HASH_COMPARE 0x400 /* Set user defined comparison function */
#define HASH_KEYCOPY 0x800 /* Set user defined key-copying function */
@@ -183,10 +123,16 @@ extern void hash_destroy(HTAB *hashp);
extern void hash_stats(const char *where, HTAB *hashp);
extern void *hash_search(HTAB *hashp, const void *keyPtr, HASHACTION action,
bool *foundPtr);
+extern uint32 get_hash_value(HTAB *hashp, const void *keyPtr);
+extern void *hash_search_with_hash_value(HTAB *hashp, const void *keyPtr,
+ uint32 hashvalue, HASHACTION action,
+ bool *foundPtr);
+extern long hash_get_num_entries(HTAB *hashp);
extern void hash_seq_init(HASH_SEQ_STATUS *status, HTAB *hashp);
extern void *hash_seq_search(HASH_SEQ_STATUS *status);
extern Size hash_estimate_size(long num_entries, Size entrysize);
extern long hash_select_dirsize(long num_entries);
+extern Size hash_get_shared_size(HASHCTL *info, int flags);
/*
* prototypes for functions in hashfn.c