Allow tupleslots to have a fixed tupledesc, use in executor nodes.

The reason for doing so is that it will allow expression evaluation to
optimize based on the underlying tupledesc. In particular it will
allow to JIT tuple deforming together with the expression itself.

For that expression initialization needs to be moved after the
relevant slots are initialized - mostly unproblematic, except in the
case of nodeWorktablescan.c.

After doing so there's no need for ExecAssignResultType() and
ExecAssignResultTypeFromTL() anymore, as all former callers have been
converted to create a slot with a fixed descriptor.

When creating a slot with a fixed descriptor, tts_values/isnull can be
allocated together with the main slot, reducing allocation overhead
and increasing cache density a bit.

Author: Andres Freund
Discussion: https://postgr.es/m/20171206093717.vqdxe5icqttpxs3p@alap3.anarazel.de

1 files changed, 11 insertions, 20 deletions

diff --git a/src/backend/executor/nodeGather.c b/src/backend/executor/nodeGather.c
index 58eadd45b83..eaf7d2d5632 100644
--- a/src/backend/executor/nodeGather.c
+++ b/src/backend/executor/nodeGather.c
@@ -59,7 +59,6 @@ ExecInitGather(Gather *node, EState *estate, int eflags)
 {
 	GatherState *gatherstate;
 	Plan	   *outerNode;
-	bool		hasoid;
 	TupleDesc	tupDesc;
 
 	/* Gather node doesn't have innerPlan node. */
@@ -86,36 +85,28 @@ ExecInitGather(Gather *node, EState *estate, int eflags)
 	ExecAssignExprContext(estate, &gatherstate->ps);
 
 	/*
-	 * Gather doesn't support checking a qual (it's always more efficient to
-	 * do it in the child node).
-	 */
-	Assert(!node->plan.qual);
-
-	/*
-	 * tuple table initialization
-	 */
-	gatherstate->funnel_slot = ExecInitExtraTupleSlot(estate);
-	ExecInitResultTupleSlot(estate, &gatherstate->ps);
-
-	/*
 	 * now initialize outer plan
 	 */
 	outerNode = outerPlan(node);
 	outerPlanState(gatherstate) = ExecInitNode(outerNode, estate, eflags);
+	tupDesc = ExecGetResultType(outerPlanState(gatherstate));
+
+	/*
+	 * Initialize result slot, type and projection.
+	 */
+	ExecInitResultTupleSlotTL(estate, &gatherstate->ps);
+	ExecConditionalAssignProjectionInfo(&gatherstate->ps, tupDesc, OUTER_VAR);
 
 	/*
 	 * Initialize funnel slot to same tuple descriptor as outer plan.
 	 */
-	if (!ExecContextForcesOids(outerPlanState(gatherstate), &hasoid))
-		hasoid = false;
-	tupDesc = ExecTypeFromTL(outerNode->targetlist, hasoid);
-	ExecSetSlotDescriptor(gatherstate->funnel_slot, tupDesc);
+	gatherstate->funnel_slot = ExecInitExtraTupleSlot(estate, tupDesc);
 
 	/*
-	 * Initialize result tuple type and projection info.
+	 * Gather doesn't support checking a qual (it's always more efficient to
+	 * do it in the child node).
 	 */
-	ExecAssignResultTypeFromTL(&gatherstate->ps);
-	ExecConditionalAssignProjectionInfo(&gatherstate->ps, tupDesc, OUTER_VAR);
+	Assert(!node->plan.qual);
 
 	return gatherstate;
 }