From 862927f4433bc759b0e8ccd57e778b1259c20b81 Mon Sep 17 00:00:00 2001
From: Bruce Momjian <bruce@momjian.us>
Date: Tue, 27 Jan 1998 03:00:43 +0000
Subject: [PATCH] Real deadlock detection.
---
src/backend/storage/lmgr/lock.c | 92 +++++++++++++++++++++++++++++----
src/backend/storage/lmgr/proc.c | 67 +++++++++++++-----------
src/include/config.h.in | 16 +++---
src/include/storage/lock.h | 4 +-
4 files changed, 130 insertions(+), 49 deletions(-)
diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c
index efc4c991ff4..286824e27f6 100644
--- a/src/backend/storage/lmgr/lock.c
+++ b/src/backend/storage/lmgr/lock.c
@@ -7,7 +7,7 @@
*
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/storage/lmgr/lock.c,v 1.21 1998/01/25 05:14:02 momjian Exp $
+ * $Header: /cvsroot/pgsql/src/backend/storage/lmgr/lock.c,v 1.22 1998/01/27 03:00:28 momjian Exp $
*
* NOTES
* Outside modules can create a lock table and acquire/release
@@ -1201,7 +1201,7 @@ LockReleaseAll(LockTableId tableId, SHM_QUEUE *lockQueue)
done = (xidLook->queue.next == end);
lock = (LOCK *) MAKE_PTR(xidLook->tag.lock);
- LOCK_PRINT("ReleaseAll", (&lock->tag), 0);
+ LOCK_PRINT("LockReleaseAll", (&lock->tag), 0);
#ifdef USER_LOCKS
@@ -1307,11 +1307,7 @@ LockReleaseAll(LockTableId tableId, SHM_QUEUE *lockQueue)
|| !found)
{
SpinRelease(masterLock);
-#ifdef USER_LOCKS
elog(NOTICE, "LockReleaseAll: xid table corrupted");
-#else
- elog(NOTICE, "LockReplace: xid table corrupted");
-#endif
return (FALSE);
}
@@ -1329,11 +1325,7 @@ LockReleaseAll(LockTableId tableId, SHM_QUEUE *lockQueue)
if ((!lock) || (!found))
{
SpinRelease(masterLock);
-#ifdef USER_LOCKS
elog(NOTICE, "LockReleaseAll: cannot remove lock from HTAB");
-#else
- elog(NOTICE, "LockReplace: cannot remove lock from HTAB");
-#endif
return (FALSE);
}
}
@@ -1415,6 +1407,86 @@ LockingDisabled()
return LockingIsDisabled;
}
+/*
+ * DeadlockCheck -- Checks for deadlocks for a given process
+ *
+ * We can't block on user locks, so no sense testing for deadlock
+ * because there is no blocking, and no timer for the block.
+ *
+ * This code takes a list of locks a process holds, and the lock that
+ * the process is sleeping on, and tries to find if any of the processes
+ * waiting on its locks hold the lock it is waiting for.
+ *
+ * We have already locked the master lock before being called.
+ */
+bool
+DeadLockCheck(SHM_QUEUE *lockQueue, LOCK *findlock, bool skip_check)
+{
+ int done;
+ XIDLookupEnt *xidLook = NULL;
+ XIDLookupEnt *tmp = NULL;
+ SHMEM_OFFSET end = MAKE_OFFSET(lockQueue);
+ LOCK *lock;
+
+ if (SHMQueueEmpty(lockQueue))
+ return false;
+
+ SHMQueueFirst(lockQueue, (Pointer *) &xidLook, &xidLook->queue);
+
+ XID_PRINT("DeadLockCheck", xidLook);
+
+ for (;;)
+ {
+ /* ---------------------------
+ * XXX Here we assume the shared memory queue is circular and
+ * that we know its internal structure. Should have some sort of
+ * macros to allow one to walk it. mer 20 July 1991
+ * ---------------------------
+ */
+ done = (xidLook->queue.next == end);
+ lock = (LOCK *) MAKE_PTR(xidLook->tag.lock);
+
+ LOCK_PRINT("DeadLockCheck", (&lock->tag), 0);
+
+ /*
+ * This is our only check to see if we found the lock we want.
+ *
+ * The lock we are waiting for is already in MyProc->lockQueue
+ * so we need to skip it here. We are trying to find it in
+ * someone else's lockQueue.
+ */
+ if (lock == findlock && !skip_check)
+ return true;
+ else if (lock != findlock || !skip_check)
+ {
+ PROC_QUEUE *waitQueue = &(lock->waitProcs);
+ PROC *proc;
+ int i;
+
+ proc = (PROC *) MAKE_PTR(waitQueue->links.prev);
+ for (i = 0; i < waitQueue->size; i++)
+ {
+ /* prevent endless loops */
+ if (proc != MyProc && skip_check)
+ {
+ /* If we found a deadlock, we can stop right now */
+ if (DeadLockCheck(&(proc->lockQueue), findlock, false))
+ return true;
+ }
+ proc = (PROC *) MAKE_PTR(proc->links.prev);
+ }
+ }
+
+ if (done)
+ break;
+ SHMQueueFirst(&xidLook->queue, (Pointer *) &tmp, &tmp->queue);
+ xidLook = tmp;
+ }
+
+ /* if we got here, no deadlock */
+ return false;
+}
+
#ifdef DEADLOCK_DEBUG
/*
* Dump all locks. Must have already acquired the masterLock.
diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c
index deca35c8d42..893ea41833d 100644
--- a/src/backend/storage/lmgr/proc.c
+++ b/src/backend/storage/lmgr/proc.c
@@ -7,7 +7,7 @@
*
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/storage/lmgr/proc.c,v 1.28 1998/01/25 05:14:09 momjian Exp $
+ * $Header: /cvsroot/pgsql/src/backend/storage/lmgr/proc.c,v 1.29 1998/01/27 03:00:29 momjian Exp $
*
*-------------------------------------------------------------------------
*/
@@ -46,7 +46,7 @@
* This is so that we can support more backends. (system-wide semaphore
* sets run out pretty fast.) -ay 4/95
*
- * $Header: /cvsroot/pgsql/src/backend/storage/lmgr/proc.c,v 1.28 1998/01/25 05:14:09 momjian Exp $
+ * $Header: /cvsroot/pgsql/src/backend/storage/lmgr/proc.c,v 1.29 1998/01/27 03:00:29 momjian Exp $
*/
#include <sys/time.h>
#include <unistd.h>
@@ -442,7 +442,7 @@ ProcQueueInit(PROC_QUEUE *queue)
* NOTES: The process queue is now a priority queue for locking.
*/
int
-ProcSleep(PROC_QUEUE *queue,
+ProcSleep(PROC_QUEUE *waitQueue,
SPINLOCK spinlock,
int token,
int prio,
@@ -453,8 +453,8 @@ ProcSleep(PROC_QUEUE *queue,
struct itimerval timeval,
dummy;
- proc = (PROC *) MAKE_PTR(queue->links.prev);
- for (i = 0; i < queue->size; i++)
+ proc = (PROC *) MAKE_PTR(waitQueue->links.prev);
+ for (i = 0; i < waitQueue->size; i++)
{
if (proc->prio >= prio)
proc = (PROC *) MAKE_PTR(proc->links.prev);
@@ -478,36 +478,38 @@ ProcSleep(PROC_QUEUE *queue,
* -------------------
*/
SHMQueueInsertTL(&(proc->links), &(MyProc->links));
- queue->size++;
+ waitQueue->size++;
SpinRelease(spinlock);
/* --------------
- * Postgres does not have any deadlock detection code and for this
- * reason we must set a timer to wake up the process in the event of
- * a deadlock. For now the timer is set for 1 minute and we assume that
- * any process which sleeps for this amount of time is deadlocked and will
- * receive a SIGALRM signal. The handler should release the processes
- * semaphore and abort the current transaction.
+ * We set this so we can wake up periodically and check for a deadlock.
+ * If a deadlock is detected, the handler releases the processes
+ * semaphore and aborts the current transaction.
*
* Need to zero out struct to set the interval and the micro seconds fields
* to 0.
* --------------
*/
MemSet(&timeval, 0, sizeof(struct itimerval));
- timeval.it_value.tv_sec = DEADLOCK_TIMEOUT;
+ timeval.it_value.tv_sec = DEADLOCK_CHECK_TIMER;
- if (setitimer(ITIMER_REAL, &timeval, &dummy))
- elog(FATAL, "ProcSleep: Unable to set timer for process wakeup");
+ do
+ {
+ MyProc->errType = NO_ERROR; /* reset flag after deadlock check */
- /* --------------
- * if someone wakes us between SpinRelease and IpcSemaphoreLock,
- * IpcSemaphoreLock will not block. The wakeup is "saved" by
- * the semaphore implementation.
- * --------------
- */
- IpcSemaphoreLock(MyProc->sem.semId, MyProc->sem.semNum, IpcExclusiveLock);
+ if (setitimer(ITIMER_REAL, &timeval, &dummy))
+ elog(FATAL, "ProcSleep: Unable to set timer for process wakeup");
+ /* --------------
+ * if someone wakes us between SpinRelease and IpcSemaphoreLock,
+ * IpcSemaphoreLock will not block. The wakeup is "saved" by
+ * the semaphore implementation.
+ * --------------
+ */
+ IpcSemaphoreLock(MyProc->sem.semId, MyProc->sem.semNum, IpcExclusiveLock);
+ } while (MyProc->errType == STATUS_NOT_FOUND); /* sleep after deadlock check */
+
/* ---------------
* We were awoken before a timeout - now disable the timer
* ---------------
@@ -615,10 +617,9 @@ ProcAddLock(SHM_QUEUE *elem)
}
/* --------------------
- * We only get to this routine if we got SIGALRM after DEADLOCK_TIMEOUT
- * while waiting for a lock to be released by some other process. After
- * the one minute deadline we assume we have a deadlock and must abort
- * this transaction. We must also indicate that I'm no longer waiting
+ * We only get to this routine if we got SIGALRM after DEADLOCK_CHECK_TIMER
+ * while waiting for a lock to be released by some other process. If we have
+ * a real deadlock, we must also indicate that I'm no longer waiting
* on a lock so that other processes don't try to wake me up and screw
* up my semaphore.
* --------------------
@@ -665,12 +666,19 @@ HandleDeadLock(int sig)
return;
}
- mywaitlock = MyProc->waitLock;
-
#ifdef DEADLOCK_DEBUG
DumpLocks();
#endif
+ if (!DeadLockCheck(&(MyProc->lockQueue), MyProc->waitLock, true))
+ {
+ UnlockLockTable();
+ MyProc->errType = STATUS_NOT_FOUND;
+ return;
+ }
+
+ mywaitlock = MyProc->waitLock;
+
/* ------------------------
* Get this process off the lock's wait queue
* ------------------------
@@ -701,8 +709,7 @@ HandleDeadLock(int sig)
*/
UnlockLockTable();
- elog(NOTICE, "Timeout interval reached -- possible deadlock.");
- elog(NOTICE, "See the lock(l) manual page for a possible cause.");
+ elog(NOTICE, "Deadlock detected -- See the lock(l) manual page for a possible cause.");
return;
}
diff --git a/src/include/config.h.in b/src/include/config.h.in
index 74f84894db7..9c0b1829c1f 100644
--- a/src/include/config.h.in
+++ b/src/include/config.h.in
@@ -210,14 +210,16 @@ extern void srandom(int seed);
code seems broken without it, Bruce Momjian */
/* #define LOARRAY */
-/* This is the time, in seconds, at which a given backend server
- * will wait on a lock before deciding to abort the transaction
- * (this is what we do in lieu of deadlock detection).
- *
- * Low numbers are not recommended as they will tend to cause
- * false aborts if many transactions are long-lived.
+/*
+ * As soon as the backend blocks on a lock, it waits this number of seconds
+ * before checking for a deadlock. If not, it keeps checking every this
+ * number of seconds.
+ * We don't check for deadlocks just before sleeping because a deadlock is
+ * a rare event, and checking is an expensive operation.
+ * We only detect deadlocks between two processes, not three or more, but
+ * these are the most common.
*/
-#define DEADLOCK_TIMEOUT 60
+#define DEADLOCK_CHECK_TIMER 60
/*
* This flag enables the use of idexes in plans generated for function
diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h
index e2a45e91203..98804eb1f08 100644
--- a/src/include/storage/lock.h
+++ b/src/include/storage/lock.h
@@ -6,7 +6,7 @@
*
* Copyright (c) 1994, Regents of the University of California
*
- * $Id: lock.h,v 1.9 1998/01/24 22:50:11 momjian Exp $
+ * $Id: lock.h,v 1.10 1998/01/27 03:00:43 momjian Exp $
*
*-------------------------------------------------------------------------
*/
@@ -214,7 +214,7 @@ extern void GrantLock(LOCK *lock, LOCKT lockt);
extern bool LockReleaseAll(LockTableId tableId, SHM_QUEUE *lockQueue);
extern int LockShmemSize(void);
extern bool LockingDisabled(void);
-
+extern bool DeadLockCheck(SHM_QUEUE *lockQueue, LOCK *findlock, bool skip_check);
#ifdef DEADLOCK_DEBUG
extern void DumpLocks(void);
--
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