Attached is a patch that fixes a gradual memory leak in ExecReScanAgg(),
when the AGG_HASHED strategy is used:
* the aggregation hash table is allocated in a newly-created
sub-context of the agg's aggcontext
* MemoryContextReset() resets the memory allocated in child
contexts, but not the child contexts themselves
* ExecReScanAgg() builds a brand-new hash table, which allocates
a brand-new sub-context, thus leaking the header for the
previous hashtable sub-context
The patch fixes this by using MemoryContextDeleteAndResetChildren(). (I
briefly looked at other call-sites of hash_create() to see if this
problem exists elsewhere, but I didn't see anything obvious.)
We run into the leak quite easily at Truviso; with a sufficiently
long-lived query in vanilla Postgres, you should be able to reproduce
the same problem.
Credit: Sailesh Krishnamurthy at Truviso for diagnosing the cause of the
leak.
-Neil
Index: src/backend/executor/nodeAgg.c
===================================================================
RCS file: /home/neilc/postgres/cvs_root/pgsql/src/backend/executor/nodeAgg.c,v
retrieving revision 1.152
diff -p -c -r1.152 nodeAgg.c
*** src/backend/executor/nodeAgg.c 2 Apr 2007 03:49:38 -0000 1.152
--- src/backend/executor/nodeAgg.c 6 Aug 2007 19:29:11 -0000
*************** ExecReScanAgg(AggState *node, ExprContex
*** 1646,1653 ****
MemSet(econtext->ecxt_aggvalues, 0, sizeof(Datum) * node->numaggs);
MemSet(econtext->ecxt_aggnulls, 0, sizeof(bool) * node->numaggs);
! /* Release all temp storage */
! MemoryContextReset(node->aggcontext);
if (((Agg *) node->ss.ps.plan)->aggstrategy == AGG_HASHED)
{
--- 1646,1657 ----
MemSet(econtext->ecxt_aggvalues, 0, sizeof(Datum) * node->numaggs);
MemSet(econtext->ecxt_aggnulls, 0, sizeof(bool) * node->numaggs);
! /*
! * Release all temp storage. Note that in the AGG_HASHED case the agg
! * hash table is allocated in a sub-context, so we need to use
! * MemoryContextResetAndDeleteChildren() to reclaim that storage.
! */
! MemoryContextResetAndDeleteChildren(node->aggcontext);
if (((Agg *) node->ss.ps.plan)->aggstrategy == AGG_HASHED)
{
---------------------------(end of broadcast)---------------------------
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