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, 5 insertions, 14 deletions

diff --git a/src/backend/executor/nodeGatherMerge.c b/src/backend/executor/nodeGatherMerge.c
index 6858c91e8c2..83221cdbaee 100644
--- a/src/backend/executor/nodeGatherMerge.c
+++ b/src/backend/executor/nodeGatherMerge.c
@@ -73,7 +73,6 @@ ExecInitGatherMerge(GatherMerge *node, EState *estate, int eflags)
 {
 	GatherMergeState *gm_state;
 	Plan	   *outerNode;
-	bool		hasoid;
 	TupleDesc	tupDesc;
 
 	/* Gather merge node doesn't have innerPlan node. */
@@ -105,11 +104,6 @@ ExecInitGatherMerge(GatherMerge *node, EState *estate, int eflags)
 	Assert(!node->plan.qual);
 
 	/*
-	 * tuple table initialization
-	 */
-	ExecInitResultTupleSlot(estate, &gm_state->ps);
-
-	/*
 	 * now initialize outer plan
 	 */
 	outerNode = outerPlan(node);
@@ -119,15 +113,13 @@ ExecInitGatherMerge(GatherMerge *node, EState *estate, int eflags)
 	 * Store the tuple descriptor into gather merge state, so we can use it
 	 * while initializing the gather merge slots.
 	 */
-	if (!ExecContextForcesOids(outerPlanState(gm_state), &hasoid))
-		hasoid = false;
-	tupDesc = ExecTypeFromTL(outerNode->targetlist, hasoid);
+	tupDesc = ExecGetResultType(outerPlanState(gm_state));
 	gm_state->tupDesc = tupDesc;
 
 	/*
-	 * Initialize result tuple type and projection info.
+	 * Initialize result slot, type and projection.
 	 */
-	ExecAssignResultTypeFromTL(&gm_state->ps);
+	ExecInitResultTupleSlotTL(estate, &gm_state->ps);
 	ExecConditionalAssignProjectionInfo(&gm_state->ps, tupDesc, OUTER_VAR);
 
 	/*
@@ -410,9 +402,8 @@ gather_merge_setup(GatherMergeState *gm_state)
 			(HeapTuple *) palloc0(sizeof(HeapTuple) * MAX_TUPLE_STORE);
 
 		/* Initialize tuple slot for worker */
-		gm_state->gm_slots[i + 1] = ExecInitExtraTupleSlot(gm_state->ps.state);
-		ExecSetSlotDescriptor(gm_state->gm_slots[i + 1],
-							  gm_state->tupDesc);
+		gm_state->gm_slots[i + 1] =
+			ExecInitExtraTupleSlot(gm_state->ps.state, gm_state->tupDesc);
 	}
 
 	/* Allocate the resources for the merge */