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, 9 deletions

diff --git a/src/backend/executor/nodeLimit.c b/src/backend/executor/nodeLimit.c
index 29d2deac23b..56d98b4490b 100644
--- a/src/backend/executor/nodeLimit.c
+++ b/src/backend/executor/nodeLimit.c
@@ -354,6 +354,12 @@ ExecInitLimit(Limit *node, EState *estate, int eflags)
 	ExecAssignExprContext(estate, &limitstate->ps);
 
 	/*
+	 * initialize outer plan
+	 */
+	outerPlan = outerPlan(node);
+	outerPlanState(limitstate) = ExecInitNode(outerPlan, estate, eflags);
+
+	/*
 	 * initialize child expressions
 	 */
 	limitstate->limitOffset = ExecInitExpr((Expr *) node->limitOffset,
@@ -362,21 +368,15 @@ ExecInitLimit(Limit *node, EState *estate, int eflags)
 										  (PlanState *) limitstate);
 
 	/*
-	 * Tuple table initialization (XXX not actually used...)
+	 * Initialize result slot and type. (XXX not actually used, but upper
+	 * nodes access it to get this node's result tupledesc...)
 	 */
-	ExecInitResultTupleSlot(estate, &limitstate->ps);
-
-	/*
-	 * then initialize outer plan
-	 */
-	outerPlan = outerPlan(node);
-	outerPlanState(limitstate) = ExecInitNode(outerPlan, estate, eflags);
+	ExecInitResultTupleSlotTL(estate, &limitstate->ps);
 
 	/*
 	 * limit nodes do no projections, so initialize projection info for this
 	 * node appropriately
 	 */
-	ExecAssignResultTypeFromTL(&limitstate->ps);
 	limitstate->ps.ps_ProjInfo = NULL;
 
 	return limitstate;