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Fix query-lifespan memory leakage in repeatedly executed hash joins.

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ExecHashTableCreate allocated some memory that wasn't freed by
ExecHashTableDestroy, specifically the per-hash-key function information.
That's not a huge amount of data, but if one runs a query that repeats
a hash join enough times, it builds up.  Fix by arranging for the data
in question to be kept in the hashtable's hashCxt instead of leaving it
"loose" in the query-lifespan executor context.  (This ensures that we'll
also clean up anything that the hash functions allocate in fn_mcxt.)

Per report from Amit Khandekar.  It's been like this forever, so back-patch
to all supported branches.

Discussion: https://postgr.es/m/CAJ3gD9cFofAWGvcxLOxDHC=B0hjtW8yGmUsF2hdGh97CM38=7g@mail.gmail.com
This commit is contained in:
Tom Lane 2018-03-16 16:03:45 -04:00
parent 013c0baadd
commit 9e17bdb8a5
1 changed files with 18 additions and 17 deletions
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35
src/backend/executor/nodeHash.c
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@ -472,7 +472,8 @@ ExecHashTableCreate(HashState *state, List *hashOperators, bool keepNulls)
* Initialize the hash table control block.
*
* The hashtable control block is just palloc'd from the executor's
* per-query memory context.
* per-query memory context. Everything else should be kept inside the
* subsidiary hashCxt or batchCxt.
*/
hashtable = (HashJoinTable) palloc(sizeof(HashJoinTableData));
hashtable->nbuckets = nbuckets;
@ -514,6 +515,22 @@ ExecHashTableCreate(HashState *state, List *hashOperators, bool keepNulls)
hashtable, nbatch, nbuckets);
#endif
/*
* Create temporary memory contexts in which to keep the hashtable working
* storage. See notes in executor/hashjoin.h.
*/
hashtable->hashCxt = AllocSetContextCreate(CurrentMemoryContext,
"HashTableContext",
ALLOCSET_DEFAULT_SIZES);
hashtable->batchCxt = AllocSetContextCreate(hashtable->hashCxt,
"HashBatchContext",
ALLOCSET_DEFAULT_SIZES);
/* Allocate data that will live for the life of the hashjoin */
oldcxt = MemoryContextSwitchTo(hashtable->hashCxt);
/*
* Get info about the hash functions to be used for each hash key. Also
* remember whether the join operators are strict.
@ -540,22 +557,6 @@ ExecHashTableCreate(HashState *state, List *hashOperators, bool keepNulls)
i++;
}
/*
* Create temporary memory contexts in which to keep the hashtable working
* storage. See notes in executor/hashjoin.h.
*/
hashtable->hashCxt = AllocSetContextCreate(CurrentMemoryContext,
"HashTableContext",
ALLOCSET_DEFAULT_SIZES);
hashtable->batchCxt = AllocSetContextCreate(hashtable->hashCxt,
"HashBatchContext",
ALLOCSET_DEFAULT_SIZES);
/* Allocate data that will live for the life of the hashjoin */
oldcxt = MemoryContextSwitchTo(hashtable->hashCxt);
if (nbatch > 1 && hashtable->parallel_state == NULL)
{
/*