From: Neil Conway <neilc@samurai.com>
Date: Wed, 8 Aug 2007 18:07:03 +0000 (+0000)
Subject: Fix a gradual memory leak in ExecReScanAgg(). Because the aggregation
X-Git-Tag: REL8_2_5~36
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=7dd8d4673f21ca63d754f2015f8b075e0dc79b91;p=postgresql

Fix a gradual memory leak in ExecReScanAgg(). Because the aggregation
hash table is allocated in a child context of the agg node's memory
context, MemoryContextReset() will reset but *not* delete the child
context. Since ExecReScanAgg() proceeds to build a new hash table
from scratch (in a new sub-context), this results in leaking the
header for the previous memory context. Therefore, use
MemoryContextResetAndDeleteChildren() instead.

Credit: My colleague Sailesh Krishnamurthy at Truviso for isolating
the cause of the leak.
---

diff --git a/src/backend/executor/nodeAgg.c b/src/backend/executor/nodeAgg.c
index 2c276b33c9..28e6d34917 100644
--- a/src/backend/executor/nodeAgg.c
+++ b/src/backend/executor/nodeAgg.c
@@ -61,7 +61,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/nodeAgg.c,v 1.146.2.1 2007/02/02 00:07:28 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/nodeAgg.c,v 1.146.2.2 2007/08/08 18:07:03 neilc Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1641,8 +1641,14 @@ ExecReScanAgg(AggState *node, ExprContext *exprCtxt)
 	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);
+	/*
+	 * Release all temp storage. Note that with AGG_HASHED, the hash table
+	 * is allocated in a sub-context of the aggcontext. We're going to
+	 * rebuild the hash table from scratch, so we need to use
+	 * MemoryContextResetAndDeleteChildren() to avoid leaking the old hash
+	 * table's memory context header.
+	 */
+	MemoryContextResetAndDeleteChildren(node->aggcontext);
 
 	if (((Agg *) node->ss.ps.plan)->aggstrategy == AGG_HASHED)
 	{