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Fix improper repetition of previous results from a hashed aggregate.

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ExecReScanAgg's check for whether it could re-use a previously calculated
hashtable neglected the possibility that the Agg node might reference
PARAM_EXEC Params that are not referenced by its input plan node.  That's
okay if the Params are in upper tlist or qual expressions; but if one
appears in aggregate input expressions, then the hashtable contents need
to be recomputed when the Param's value changes.

To avoid unnecessary performance degradation in the case of a Param that
isn't within an aggregate input, add logic to the planner to determine
which Params are within aggregate inputs.  This requires a new field in
struct Agg, but fortunately we never write plans to disk, so this isn't
an initdb-forcing change.

Per report from Jeevan Chalke.  This has been broken since forever,
so back-patch to all supported branches.

Andrew Gierth, with minor adjustments by me

Report: <CAM2+6=VY8ykfLT5Q8vb9B6EbeBk-NGuLbT6seaQ+Fq4zXvrDcA@mail.gmail.com>
This commit is contained in:
Tom Lane
2016-08-24 14:37:50 -04:00
parent 5cd3864075
commit 2c00fad286
9 changed files with 156 additions and 6 deletions
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10
src/backend/executor/nodeAgg.c
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@ -3425,11 +3425,13 @@ ExecReScanAgg(AggState *node)
return;
/*
* If we do have the hash table and the subplan does not have any
* parameter changes, then we can just rescan the existing hash table;
* no need to build it again.
* If we do have the hash table, and the subplan does not have any
* parameter changes, and none of our own parameter changes affect
* input expressions of the aggregated functions, then we can just
* rescan the existing hash table; no need to build it again.
*/
if (outerPlan->chgParam == NULL)
if (outerPlan->chgParam == NULL &&
!bms_overlap(node->ss.ps.chgParam, aggnode->aggParams))
{
ResetTupleHashIterator(node->hashtable, &node->hashiter);
return;