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 8023f268f4a6908d1a0983f205ff9af2418d87ab..a61c885b9e008cc96810bb51f3b402b1c3fbd97f 100644 (file)
--- a/src/backend/executor/nodeAgg.c
+++ b/src/backend/executor/nodeAgg.c
@@ -1509,8 +1509,14 @@ 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)
        {