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>

2 files changed, 95 insertions, 0 deletions

diff --git a/src/test/regress/expected/aggregates.out b/src/test/regress/expected/aggregates.out
index d35cc669f7e..99be5bb2355 100644
--- a/src/test/regress/expected/aggregates.out
+++ b/src/test/regress/expected/aggregates.out
@@ -305,6 +305,79 @@ from tenk1 o;
  9999
 (1 row)
 
+-- Test handling of Params within aggregate arguments in hashed aggregation.
+-- Per bug report from Jeevan Chalke.
+explain (verbose, costs off)
+select s1, s2, sm
+from generate_series(1, 3) s1,
+     lateral (select s2, sum(s1 + s2) sm
+              from generate_series(1, 3) s2 group by s2) ss
+order by 1, 2;
+                            QUERY PLAN                            
+------------------------------------------------------------------
+ Sort
+   Output: s1.s1, s2.s2, (sum((s1.s1 + s2.s2)))
+   Sort Key: s1.s1, s2.s2
+   ->  Nested Loop
+         Output: s1.s1, s2.s2, (sum((s1.s1 + s2.s2)))
+         ->  Function Scan on pg_catalog.generate_series s1
+               Output: s1.s1
+               Function Call: generate_series(1, 3)
+         ->  HashAggregate
+               Output: s2.s2, sum((s1.s1 + s2.s2))
+               ->  Function Scan on pg_catalog.generate_series s2
+                     Output: s2.s2
+                     Function Call: generate_series(1, 3)
+(13 rows)
+
+select s1, s2, sm
+from generate_series(1, 3) s1,
+     lateral (select s2, sum(s1 + s2) sm
+              from generate_series(1, 3) s2 group by s2) ss
+order by 1, 2;
+ s1 | s2 | sm 
+----+----+----
+  1 |  1 |  2
+  1 |  2 |  3
+  1 |  3 |  4
+  2 |  1 |  3
+  2 |  2 |  4
+  2 |  3 |  5
+  3 |  1 |  4
+  3 |  2 |  5
+  3 |  3 |  6
+(9 rows)
+
+explain (verbose, costs off)
+select array(select sum(x+y) s
+            from generate_series(1,3) y group by y order by s)
+  from generate_series(1,3) x;
+                            QUERY PLAN                             
+-------------------------------------------------------------------
+ Function Scan on pg_catalog.generate_series x
+   Output: (SubPlan 1)
+   Function Call: generate_series(1, 3)
+   SubPlan 1
+     ->  Sort
+           Output: (sum((x.x + y.y))), y.y
+           Sort Key: (sum((x.x + y.y)))
+           ->  HashAggregate
+                 Output: sum((x.x + y.y)), y.y
+                 ->  Function Scan on pg_catalog.generate_series y
+                       Output: y.y
+                       Function Call: generate_series(1, 3)
+(12 rows)
+
+select array(select sum(x+y) s
+            from generate_series(1,3) y group by y order by s)
+  from generate_series(1,3) x;
+  array  
+---------
+ {2,3,4}
+ {3,4,5}
+ {4,5,6}
+(3 rows)
+
 --
 -- test for bitwise integer aggregates
 --
diff --git a/src/test/regress/sql/aggregates.sql b/src/test/regress/sql/aggregates.sql
index fb47169c0fd..9bd5233f9c9 100644
--- a/src/test/regress/sql/aggregates.sql
+++ b/src/test/regress/sql/aggregates.sql
@@ -86,6 +86,28 @@ select
   (select max((select i.unique2 from tenk1 i where i.unique1 = o.unique1)))
 from tenk1 o;
 
+-- Test handling of Params within aggregate arguments in hashed aggregation.
+-- Per bug report from Jeevan Chalke.
+explain (verbose, costs off)
+select s1, s2, sm
+from generate_series(1, 3) s1,
+     lateral (select s2, sum(s1 + s2) sm
+              from generate_series(1, 3) s2 group by s2) ss
+order by 1, 2;
+select s1, s2, sm
+from generate_series(1, 3) s1,
+     lateral (select s2, sum(s1 + s2) sm
+              from generate_series(1, 3) s2 group by s2) ss
+order by 1, 2;
+
+explain (verbose, costs off)
+select array(select sum(x+y) s
+            from generate_series(1,3) y group by y order by s)
+  from generate_series(1,3) x;
+select array(select sum(x+y) s
+            from generate_series(1,3) y group by y order by s)
+  from generate_series(1,3) x;
+
 --
 -- test for bitwise integer aggregates
 --