From 969f9d0b4ba574bb8df65683dbf7a09c030f3e67 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Sat, 11 Apr 2020 12:39:19 -0400 Subject: Make EXPLAIN report maximum hashtable usage across multiple rescans. Before discarding the old hash table in ExecReScanHashJoin, capture its statistics, ensuring that we report the maximum hashtable size across repeated rescans of the hash input relation. We can repurpose the existing code for reporting hashtable size in parallel workers to help with this, making the patch pretty small. This also ensures that if rescans happen within parallel workers, we get the correct maximums across all instances. Konstantin Knizhnik and Tom Lane, per diagnosis by Thomas Munro of a trouble report from Alvaro Herrera. Discussion: https://postgr.es/m/20200323165059.GA24950@alvherre.pgsql --- src/backend/executor/nodeHashjoin.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) (limited to 'src/backend/executor/nodeHashjoin.c') diff --git a/src/backend/executor/nodeHashjoin.c b/src/backend/executor/nodeHashjoin.c index 9e28ddd8951..cc8edacdd01 100644 --- a/src/backend/executor/nodeHashjoin.c +++ b/src/backend/executor/nodeHashjoin.c @@ -1338,8 +1338,16 @@ ExecReScanHashJoin(HashJoinState *node) /* must destroy and rebuild hash table */ HashState *hashNode = castNode(HashState, innerPlanState(node)); - /* for safety, be sure to clear child plan node's pointer too */ Assert(hashNode->hashtable == node->hj_HashTable); + /* accumulate stats from old hash table, if wanted */ + /* (this should match ExecShutdownHash) */ + if (hashNode->ps.instrument && !hashNode->hinstrument) + hashNode->hinstrument = (HashInstrumentation *) + palloc0(sizeof(HashInstrumentation)); + if (hashNode->hinstrument) + ExecHashAccumInstrumentation(hashNode->hinstrument, + hashNode->hashtable); + /* for safety, be sure to clear child plan node's pointer too */ hashNode->hashtable = NULL; ExecHashTableDestroy(node->hj_HashTable); -- cgit v1.2.3