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Commit6f90690

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Fix WaitOnLock() to ensure that the process's "waiting" flag is reset after
erroring out of a wait. We can use a PG_TRY block for this, but add a commentexplaining why it'd be a bad idea to use it for any other state cleanup.Back-patch to 8.2. Prior releases had the same issue, but only with respectto the process title, which is likely to get reset almost immediately anywayafter the transaction aborts, so it seems not worth changing them. In 8.2and HEAD, the pg_stat_activity "waiting" flag could remain set incorrectlyfor a long time.Per report from Gurjeet Singh.
1 parent9e647a1 commit6f90690

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1 file changed

+47
-22
lines changed
  • src/backend/storage/lmgr

1 file changed

+47
-22
lines changed

‎src/backend/storage/lmgr/lock.c‎

Lines changed: 47 additions & 22 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/backend/storage/lmgr/lock.c,v 1.180 2008/01/01 19:45:52 momjian Exp $
11+
* $PostgreSQL: pgsql/src/backend/storage/lmgr/lock.c,v 1.181 2008/02/02 22:26:17 tgl Exp $
1212
*
1313
* NOTES
1414
* A lock table is a shared memory hash table. When
@@ -1102,16 +1102,17 @@ WaitOnLock(LOCALLOCK *locallock, ResourceOwner owner)
11021102
{
11031103
LOCKMETHODIDlockmethodid=LOCALLOCK_LOCKMETHOD(*locallock);
11041104
LockMethodlockMethodTable=LockMethods[lockmethodid];
1105-
constchar*old_status;
1106-
char*new_status=NULL;
1107-
intlen;
1105+
char*volatilenew_status=NULL;
11081106

11091107
LOCK_PRINT("WaitOnLock: sleeping on lock",
11101108
locallock->lock,locallock->tag.mode);
11111109

11121110
/* Report change to waiting status */
11131111
if (update_process_title)
11141112
{
1113+
constchar*old_status;
1114+
intlen;
1115+
11151116
old_status=get_ps_display(&len);
11161117
new_status= (char*)palloc(len+8+1);
11171118
memcpy(new_status,old_status,len);
@@ -1132,38 +1133,62 @@ WaitOnLock(LOCALLOCK *locallock, ResourceOwner owner)
11321133
* that a cancel/die interrupt will interrupt ProcSleep after someone else
11331134
* grants us the lock, but before we've noticed it. Hence, after granting,
11341135
* the locktable state must fully reflect the fact that we own the lock;
1135-
* we can't do additional work on return. Contrariwise, if we fail, any
1136-
* cleanup must happen in xact abort processing, not here, to ensure it
1137-
* will also happen in the cancel/die case.
1136+
* we can't do additional work on return.
1137+
*
1138+
* We can and do use a PG_TRY block to try to clean up after failure,
1139+
* but this still has a major limitation: elog(FATAL) can occur while
1140+
* waiting (eg, a "die" interrupt), and then control won't come back here.
1141+
* So all cleanup of essential state should happen in LockWaitCancel,
1142+
* not here. We can use PG_TRY to clear the "waiting" status flags,
1143+
* since doing that is unimportant if the process exits.
11381144
*/
1145+
PG_TRY();
1146+
{
1147+
if (ProcSleep(locallock,lockMethodTable)!=STATUS_OK)
1148+
{
1149+
/*
1150+
* We failed as a result of a deadlock, see CheckDeadLock().
1151+
* Quit now.
1152+
*/
1153+
awaitedLock=NULL;
1154+
LOCK_PRINT("WaitOnLock: aborting on lock",
1155+
locallock->lock,locallock->tag.mode);
1156+
LWLockRelease(LockHashPartitionLock(locallock->hashcode));
11391157

1140-
if (ProcSleep(locallock,lockMethodTable)!=STATUS_OK)
1158+
/*
1159+
* Now that we aren't holding the partition lock, we can give an
1160+
* error report including details about the detected deadlock.
1161+
*/
1162+
DeadLockReport();
1163+
/* not reached */
1164+
}
1165+
}
1166+
PG_CATCH();
11411167
{
1142-
/*
1143-
* We failed as a result of a deadlock, see CheckDeadLock(). Quit now.
1144-
*/
1145-
awaitedLock=NULL;
1146-
LOCK_PRINT("WaitOnLock: aborting on lock",
1147-
locallock->lock,locallock->tag.mode);
1148-
LWLockRelease(LockHashPartitionLock(locallock->hashcode));
1168+
/* In this path, awaitedLock remains set until LockWaitCancel */
11491169

1150-
/*
1151-
* Now that we aren't holding the partition lock, we can give an error
1152-
* report including details about the detected deadlock.
1153-
*/
1154-
DeadLockReport();
1155-
/* not reached */
1170+
/* Report change to non-waiting status */
1171+
pgstat_report_waiting(false);
1172+
if (update_process_title)
1173+
{
1174+
set_ps_display(new_status, false);
1175+
pfree(new_status);
1176+
}
1177+
1178+
/* and propagate the error */
1179+
PG_RE_THROW();
11561180
}
1181+
PG_END_TRY();
11571182

11581183
awaitedLock=NULL;
11591184

11601185
/* Report change to non-waiting status */
1186+
pgstat_report_waiting(false);
11611187
if (update_process_title)
11621188
{
11631189
set_ps_display(new_status, false);
11641190
pfree(new_status);
11651191
}
1166-
pgstat_report_waiting(false);
11671192

11681193
LOCK_PRINT("WaitOnLock: wakeup on lock",
11691194
locallock->lock,locallock->tag.mode);

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