Fix improper repetition of previous results from a hashed aggregate.

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>

1 files changed, 2 insertions, 0 deletions

diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
index 3b9c6838295..fab1c3b820c 100644
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -631,6 +631,8 @@ typedef struct Agg
 	AttrNumber *grpColIdx;		/* their indexes in the target list */
 	Oid		   *grpOperators;	/* equality operators to compare with */
 	long		numGroups;		/* estimated number of groups in input */
+	Bitmapset  *aggParams;		/* IDs of Params used in Aggref inputs */
+	/* Note: planner provides numGroups & aggParams only in AGG_HASHED case */
 } Agg;
 
 /* ----------------