3 files changed, 21 insertions, 0 deletions
diff --git a/src/backend/executor/nodeAgg.c b/src/backend/executor/nodeAgg.c
index 08088ea3c0c..8079d977643 100644
--- a/src/backend/executor/nodeAgg.c
+++ b/src/backend/executor/nodeAgg.c
@@ -363,6 +363,10 @@ initialize_aggregates(AggState *aggstate,
 			 * We use a plain Datum sorter when there's a single input column;
 			 * otherwise sort the full tuple.  (See comments for
 			 * process_ordered_aggregate_single.)
+			 *
+			 * In the future, we should consider forcing the
+			 * tuplesort_begin_heap() case when the abbreviated key
+			 * optimization can thereby be used, even when numInputs is 1.
 			 */
 			peraggstate->sortstate =
 				(peraggstate->numInputs == 1) ?
diff --git a/src/backend/executor/nodeMergeAppend.c b/src/backend/executor/nodeMergeAppend.c
index 4e200a8e346..0c814f0e72d 100644
--- a/src/backend/executor/nodeMergeAppend.c
+++ b/src/backend/executor/nodeMergeAppend.c
@@ -137,6 +137,15 @@ ExecInitMergeAppend(MergeAppend *node, EState *estate, int eflags)
 		sortKey->ssup_nulls_first = node->nullsFirst[i];
 		sortKey->ssup_attno = node->sortColIdx[i];
 
+		/*
+		 * It isn't feasible to perform abbreviated key conversion, since
+		 * tuples are pulled into mergestate's binary heap as needed.  It would
+		 * likely be counter-productive to convert tuples into an abbreviated
+		 * representation as they're pulled up, so opt out of that additional
+		 * optimization entirely.
+		 */
+		sortKey->abbreviate = false;
+
 		PrepareSortSupportFromOrderingOp(node->sortOperators[i], sortKey);
 	}
 
diff --git a/src/backend/executor/nodeMergejoin.c b/src/backend/executor/nodeMergejoin.c
index 2a5a7acf945..15742c574ad 100644
--- a/src/backend/executor/nodeMergejoin.c
+++ b/src/backend/executor/nodeMergejoin.c
@@ -229,6 +229,14 @@ MJExamineQuals(List *mergeclauses,
 			elog(ERROR, "cannot merge using non-equality operator %u",
 				 qual->opno);
 
+		/*
+		 * sortsupport routine must know if abbreviation optimization is
+		 * applicable in principle.  It is never applicable for merge joins
+		 * because there is no convenient opportunity to convert to alternative
+		 * representation.
+		 */
+		clause->ssup.abbreviate = false;
+
 		/* And get the matching support or comparison function */
 		Assert(clause->ssup.comparator == NULL);
 		sortfunc = get_opfamily_proc(opfamily,