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Commit57f5939

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Delay build of Memoize hash table until executor run
Previously this hash table was built during executor startup. Thiscould cause long delays in EXPLAIN (without ANALYZE) when the planneropts to use a large Memoize hash table.No backpatch for now due to lack of complaints.Author: David RowleyDiscussion:https://postgr.es/m/CAApHDvoJktJ5XL=Kjh2a2TFr64R-7eQZV-+jcJrUwoES2GLiWg@mail.gmail.com
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‎src/backend/executor/nodeMemoize.c

Lines changed: 20 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -278,11 +278,14 @@ MemoizeHash_equal(struct memoize_hash *tb, const MemoizeKey *key1,
278278
}
279279

280280
/*
281-
* Initialize the hash table to empty.
281+
* Initialize the hash table to empty. The MemoizeState's hashtable field
282+
* must point to NULL.
282283
*/
283284
staticvoid
284285
build_hash_table(MemoizeState*mstate,uint32size)
285286
{
287+
Assert(mstate->hashtable==NULL);
288+
286289
/* Make a guess at a good size when we're not given a valid size. */
287290
if (size==0)
288291
size=1024;
@@ -400,8 +403,10 @@ remove_cache_entry(MemoizeState *mstate, MemoizeEntry *entry)
400403
staticvoid
401404
cache_purge_all(MemoizeState*mstate)
402405
{
403-
uint64evictions=mstate->hashtable->members;
404-
PlanState*pstate= (PlanState*)mstate;
406+
uint64evictions=0;
407+
408+
if (mstate->hashtable!=NULL)
409+
evictions=mstate->hashtable->members;
405410

406411
/*
407412
* Likely the most efficient way to remove all items is to just reset the
@@ -410,8 +415,8 @@ cache_purge_all(MemoizeState *mstate)
410415
*/
411416
MemoryContextReset(mstate->tableContext);
412417

413-
/*Make the hash table thesame size astheoriginal size */
414-
build_hash_table(mstate, ((Memoize*)pstate->plan)->est_entries);
418+
/*NULLify so we recreate thetable onthenext call */
419+
mstate->hashtable=NULL;
415420

416421
/* reset the LRU list */
417422
dlist_init(&mstate->lru_list);
@@ -707,6 +712,10 @@ ExecMemoize(PlanState *pstate)
707712

708713
Assert(node->entry==NULL);
709714

715+
/* first call? we'll need a hash table. */
716+
if (unlikely(node->hashtable==NULL))
717+
build_hash_table(node, ((Memoize*)pstate->plan)->est_entries);
718+
710719
/*
711720
* We're only ever in this state for the first call of the
712721
* scan. Here we have a look to see if we've already seen the
@@ -1051,8 +1060,11 @@ ExecInitMemoize(Memoize *node, EState *estate, int eflags)
10511060
/* Zero the statistics counters */
10521061
memset(&mstate->stats,0,sizeof(MemoizeInstrumentation));
10531062

1054-
/* Allocate and set up the actual cache */
1055-
build_hash_table(mstate,node->est_entries);
1063+
/*
1064+
* Because it may require a large allocation, we delay building of the
1065+
* hash table until executor run.
1066+
*/
1067+
mstate->hashtable=NULL;
10561068

10571069
returnmstate;
10581070
}
@@ -1062,6 +1074,7 @@ ExecEndMemoize(MemoizeState *node)
10621074
{
10631075
#ifdefUSE_ASSERT_CHECKING
10641076
/* Validate the memory accounting code is correct in assert builds. */
1077+
if (node->hashtable!=NULL)
10651078
{
10661079
intcount;
10671080
uint64mem=0;

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