From: Ronan Dunklau <ronan.dunklau@aiven.io>
Date: Mon, 5 Jul 2021 12:45:26 +0200
Subject: [PATCH] Allow Sort nodes to use the fast "single datum" tuplesort.

The sorting code in nodeagg made use of this API, but not the regular
nodesort one. This is a POC seeing how it can be done.
---
 src/backend/executor/nodeSort.c | 62 +++++++++++++++++++++++++--------
 src/include/nodes/execnodes.h   |  1 +
 2 files changed, 48 insertions(+), 15 deletions(-)

diff --git a/src/backend/executor/nodeSort.c b/src/backend/executor/nodeSort.c
index b99027e0d7..03873b0d58 100644
--- a/src/backend/executor/nodeSort.c
+++ b/src/backend/executor/nodeSort.c
@@ -44,6 +44,7 @@ ExecSort(PlanState *pstate)
 	ScanDirection dir;
 	Tuplesortstate *tuplesortstate;
 	TupleTableSlot *slot;
+	Sort	   *plannode = (Sort *) node->ss.ps.plan;
 
 	CHECK_FOR_INTERRUPTS();
 
@@ -64,7 +65,6 @@ ExecSort(PlanState *pstate)
 
 	if (!node->sort_Done)
 	{
-		Sort	   *plannode = (Sort *) node->ss.ps.plan;
 		PlanState  *outerNode;
 		TupleDesc	tupDesc;
 
@@ -85,16 +85,29 @@ ExecSort(PlanState *pstate)
 
 		outerNode = outerPlanState(node);
 		tupDesc = ExecGetResultType(outerNode);
+		if ((tupDesc->natts == 1) &&
+			(TupleDescAttr(tupDesc, 0) ->attbyval) &&
+			!node->bounded)
+		{
 
-		tuplesortstate = tuplesort_begin_heap(tupDesc,
-											  plannode->numCols,
-											  plannode->sortColIdx,
-											  plannode->sortOperators,
-											  plannode->collations,
-											  plannode->nullsFirst,
-											  work_mem,
-											  NULL,
-											  node->randomAccess);
+			node->is_single_val = true;
+			tuplesortstate = tuplesort_begin_datum(TupleDescAttr(tupDesc, 0)->atttypid,
+												   plannode->sortOperators[0],
+												   plannode->collations[0],
+												   plannode->nullsFirst[0],
+												   work_mem,
+												   NULL,
+												   node->randomAccess);
+		} else
+			tuplesortstate = tuplesort_begin_heap(tupDesc,
+												  plannode->numCols,
+												  plannode->sortColIdx,
+												  plannode->sortOperators,
+												  plannode->collations,
+												  plannode->nullsFirst,
+												  work_mem,
+												  NULL,
+												  node->randomAccess);
 		if (node->bounded)
 			tuplesort_set_bound(tuplesortstate, node->bound);
 		node->tuplesortstate = (void *) tuplesortstate;
@@ -109,8 +122,15 @@ ExecSort(PlanState *pstate)
 
 			if (TupIsNull(slot))
 				break;
-
-			tuplesort_puttupleslot(tuplesortstate, slot);
+			if(node->is_single_val)
+			{
+				slot_getsomeattrs(slot, 1);
+				tuplesort_putdatum(tuplesortstate,
+								   slot->tts_values[0],
+								   slot->tts_isnull[0]);
+			} else {
+				tuplesort_puttupleslot(tuplesortstate, slot);
+			}
 		}
 
 		/*
@@ -150,9 +170,17 @@ ExecSort(PlanState *pstate)
 	 * next fetch from the tuplesort.
 	 */
 	slot = node->ss.ps.ps_ResultTupleSlot;
-	(void) tuplesort_gettupleslot(tuplesortstate,
-								  ScanDirectionIsForward(dir),
-								  false, slot, NULL);
+	if (node->is_single_val)
+	{
+		ExecClearTuple(slot);
+		if(tuplesort_getdatum(tuplesortstate, ScanDirectionIsForward(dir),
+						   &(slot->tts_values[0]), &(slot->tts_isnull[0]), NULL))
+			ExecStoreVirtualTuple(slot);
+	}
+	else
+		(void) tuplesort_gettupleslot(tuplesortstate,
+									  ScanDirectionIsForward(dir),
+									  false, slot, NULL);
 	return slot;
 }
 
@@ -167,6 +195,7 @@ SortState *
 ExecInitSort(Sort *node, EState *estate, int eflags)
 {
 	SortState  *sortstate;
+	TupleDesc out_tuple_desc;
 
 	SO1_printf("ExecInitSort: %s\n",
 			   "initializing sort node");
@@ -191,6 +220,7 @@ ExecInitSort(Sort *node, EState *estate, int eflags)
 	sortstate->bounded = false;
 	sortstate->sort_Done = false;
 	sortstate->tuplesortstate = NULL;
+	sortstate->is_single_val = false;
 
 	/*
 	 * Miscellaneous initialization
@@ -208,6 +238,8 @@ ExecInitSort(Sort *node, EState *estate, int eflags)
 	eflags &= ~(EXEC_FLAG_REWIND | EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK);
 
 	outerPlanState(sortstate) = ExecInitNode(outerPlan(node), estate, eflags);
+	out_tuple_desc = outerPlanState(sortstate)->ps_ResultTupleDesc;
+
 
 	/*
 	 * Initialize scan slot and type.
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 0ec5509e7e..643f416c54 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -2151,6 +2151,7 @@ typedef struct SortState
 	int64		bound_Done;		/* value of bound we did the sort with */
 	void	   *tuplesortstate; /* private state of tuplesort.c */
 	bool		am_worker;		/* are we a worker? */
+	bool		is_single_val;  /* are we using the single value optimization ? */
 	SharedSortInfo *shared_info;	/* one entry per worker */
 } SortState;
 
-- 
2.32.0


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