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, 9 insertions, 14 deletions

diff --git a/src/backend/executor/nodeHash.c b/src/backend/executor/nodeHash.c
index b10f8474527..06bb44b1631 100644
--- a/src/backend/executor/nodeHash.c
+++ b/src/backend/executor/nodeHash.c
@@ -374,28 +374,23 @@ ExecInitHash(Hash *node, EState *estate, int eflags)
 	ExecAssignExprContext(estate, &hashstate->ps);
 
 	/*
-	 * initialize our result slot
-	 */
-	ExecInitResultTupleSlot(estate, &hashstate->ps);
-
-	/*
-	 * initialize child expressions
-	 */
-	hashstate->ps.qual =
-		ExecInitQual(node->plan.qual, (PlanState *) hashstate);
-
-	/*
 	 * initialize child nodes
 	 */
 	outerPlanState(hashstate) = ExecInitNode(outerPlan(node), estate, eflags);
 
 	/*
-	 * initialize tuple type. no need to initialize projection info because
-	 * this node doesn't do projections
+	 * initialize our result slot and type. No need to build projection
+	 * because this node doesn't do projections.
 	 */
-	ExecAssignResultTypeFromTL(&hashstate->ps);
+	ExecInitResultTupleSlotTL(estate, &hashstate->ps);
 	hashstate->ps.ps_ProjInfo = NULL;
 
+	/*
+	 * initialize child expressions
+	 */
+	hashstate->ps.qual =
+		ExecInitQual(node->plan.qual, (PlanState *) hashstate);
+
 	return hashstate;
 }