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>

src/backend/executor/nodeAgg.c

@@ -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;

src/backend/nodes/copyfuncs.c

@@ -877,6 +877,7 @@ _copyAgg(const Agg *from)
 		COPY_POINTER_FIELD(grpOperators, from->numCols * sizeof(Oid));
 	}
 	COPY_SCALAR_FIELD(numGroups);
+	COPY_BITMAPSET_FIELD(aggParams);
 	COPY_NODE_FIELD(groupingSets);
 	COPY_NODE_FIELD(chain);
 

src/backend/nodes/outfuncs.c

@@ -716,6 +716,7 @@ _outAgg(StringInfo str, const Agg *node)
 		appendStringInfo(str, " %u", node->grpOperators[i]);
 
 	WRITE_LONG_FIELD(numGroups);
+	WRITE_BITMAPSET_FIELD(aggParams);
 	WRITE_NODE_FIELD(groupingSets);
 	WRITE_NODE_FIELD(chain);
 }

src/backend/nodes/readfuncs.c

@@ -2007,6 +2007,7 @@ _readAgg(void)
 	READ_ATTRNUMBER_ARRAY(grpColIdx, local_node->numCols);
 	READ_OID_ARRAY(grpOperators, local_node->numCols);
 	READ_LONG_FIELD(numGroups);
+	READ_BITMAPSET_FIELD(aggParams);
 	READ_NODE_FIELD(groupingSets);
 	READ_NODE_FIELD(chain);
 

src/backend/optimizer/plan/createplan.c

@@ -5664,6 +5664,7 @@ make_agg(List *tlist, List *qual,
 	node->grpColIdx = grpColIdx;
 	node->grpOperators = grpOperators;
 	node->numGroups = numGroups;
+	node->aggParams = NULL;		/* SS_finalize_plan() will fill this */
 	node->groupingSets = groupingSets;
 	node->chain = chain;
 

src/backend/optimizer/plan/subselect.c

@@ -82,6 +82,7 @@ static Bitmapset *finalize_plan(PlannerInfo *root,
 			  Bitmapset *valid_params,
 			  Bitmapset *scan_params);
 static bool finalize_primnode(Node *node, finalize_primnode_context *context);
+static bool finalize_agg_primnode(Node *node, finalize_primnode_context *context);
 
 
 /*
@@ -2652,6 +2653,29 @@ finalize_plan(PlannerInfo *root, Plan *plan, Bitmapset *valid_params,
 										 locally_added_param);
 			break;
 
+		case T_Agg:
+			{
+				Agg		   *agg = (Agg *) plan;
+
+				/*
+				 * AGG_HASHED plans need to know which Params are referenced
+				 * in aggregate calls.  Do a separate scan to identify them.
+				 */
+				if (agg->aggstrategy == AGG_HASHED)
+				{
+					finalize_primnode_context aggcontext;
+
+					aggcontext.root = root;
+					aggcontext.paramids = NULL;
+					finalize_agg_primnode((Node *) agg->plan.targetlist,
+										  &aggcontext);
+					finalize_agg_primnode((Node *) agg->plan.qual,
+										  &aggcontext);
+					agg->aggParams = aggcontext.paramids;
+				}
+			}
+			break;
+
 		case T_WindowAgg:
 			finalize_primnode(((WindowAgg *) plan)->startOffset,
 							  &context);
@@ -2660,7 +2684,6 @@ finalize_plan(PlannerInfo *root, Plan *plan, Bitmapset *valid_params,
 			break;
 
 		case T_Hash:
-		case T_Agg:
 		case T_Material:
 		case T_Sort:
 		case T_Unique:
@@ -2811,6 +2834,29 @@ finalize_primnode(Node *node, finalize_primnode_context *context)
 								  (void *) context);
 }
 
+/*
+ * finalize_agg_primnode: find all Aggref nodes in the given expression tree,
+ * and add IDs of all PARAM_EXEC params appearing within their aggregated
+ * arguments to the result set.
+ */
+static bool
+finalize_agg_primnode(Node *node, finalize_primnode_context *context)
+{
+	if (node == NULL)
+		return false;
+	if (IsA(node, Aggref))
+	{
+		Aggref	   *agg = (Aggref *) node;
+
+		/* we should not consider the direct arguments, if any */
+		finalize_primnode((Node *) agg->args, context);
+		finalize_primnode((Node *) agg->aggfilter, context);
+		return false;			/* there can't be any Aggrefs below here */
+	}
+	return expression_tree_walker(node, finalize_agg_primnode,
+								  (void *) context);
+}
+
 /*
  * SS_make_initplan_output_param - make a Param for an initPlan's output
  *

src/include/nodes/plannodes.h

@@ -715,7 +715,8 @@ 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 */
-	/* Note: the planner only provides numGroups in AGG_HASHED case */
+	Bitmapset  *aggParams;		/* IDs of Params used in Aggref inputs */
+	/* Note: planner provides numGroups & aggParams only in AGG_HASHED case */
 	List	   *groupingSets;	/* grouping sets to use */
 	List	   *chain;			/* chained Agg/Sort nodes */
 } Agg;

src/test/regress/expected/aggregates.out

@@ -366,6 +366,81 @@ 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))
+               Group Key: s2.s2
+               ->  Function Scan on pg_catalog.generate_series s2
+                     Output: s2.s2
+                     Function Call: generate_series(1, 3)
+(14 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
+                 Group Key: y.y
+                 ->  Function Scan on pg_catalog.generate_series y
+                       Output: y.y
+                       Function Call: generate_series(1, 3)
+(13 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
 --

src/test/regress/sql/aggregates.sql

@@ -98,6 +98,28 @@ 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
 --