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Avoid memory leakage when a series of subtransactions invoke AFTER triggers

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that are fired at end-of-statement (as is the normal case for foreign keys,
for example).  In this situation the per-subxact deferred trigger context
is always empty when subtransaction exit is reached; so we could free it,
but were not doing so, leading to an intratransaction leak of 8K or more
per subtransaction.  Per off-list example from Viatcheslav Kalinin
subsequent to bug #3418 (his original bug report omitted a foreign key
constraint needed to cause this leak).

Back-patch to 8.2; prior versions were not using per-subxact contexts
for deferred triggers, so did not have this leak.
This commit is contained in:
Tom Lane 2007-07-01 17:45:42 +00:00
parent beba73763b
commit 8f55b9a8ba
1 changed files with 19 additions and 1 deletions
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20
src/backend/commands/trigger.c
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@ -7,7 +7,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/commands/trigger.c,v 1.214 2007/03/19 23:38:29 wieck Exp $
* $PostgreSQL: pgsql/src/backend/commands/trigger.c,v 1.215 2007/07/01 17:45:42 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -2814,6 +2814,24 @@ AfterTriggerEndSubXact(bool isCommit)
afterTriggers->state_stack[my_level] = NULL;
Assert(afterTriggers->query_depth ==
afterTriggers->depth_stack[my_level]);
/*
* It's entirely possible that the subxact created an event_cxt but
* there is not anything left in it (because all the triggers were
* fired at end-of-statement). If so, we should release the context
* to prevent memory leakage in a long sequence of subtransactions.
* We can detect whether there's anything of use in the context by
* seeing if anything was added to the global events list since
* subxact start. (This test doesn't catch every case where the
* context is deletable; for instance maybe the only additions were
* from a sub-sub-xact. But it handles the common case.)
*/
if (afterTriggers->cxt_stack[my_level] &&
afterTriggers->events.tail == afterTriggers->events_stack[my_level].tail)
{
MemoryContextDelete(afterTriggers->cxt_stack[my_level]);
/* avoid double delete if abort later */
afterTriggers->cxt_stack[my_level] = NULL;
}
}
else
{