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, 16 deletions

diff --git a/src/backend/executor/nodeValuesscan.c b/src/backend/executor/nodeValuesscan.c
index c3d78b6295e..63b7e7ef5b8 100644
--- a/src/backend/executor/nodeValuesscan.c
+++ b/src/backend/executor/nodeValuesscan.c
@@ -248,23 +248,22 @@ ExecInitValuesScan(ValuesScan *node, EState *estate, int eflags)
 	ExecAssignExprContext(estate, planstate);
 
 	/*
-	 * tuple table initialization
+	 * Get info about values list, initialize scan slot with it.
 	 */
-	ExecInitResultTupleSlot(estate, &scanstate->ss.ps);
-	ExecInitScanTupleSlot(estate, &scanstate->ss);
+	tupdesc = ExecTypeFromExprList((List *) linitial(node->values_lists));
+	ExecInitScanTupleSlot(estate, &scanstate->ss, tupdesc);
 
 	/*
-	 * initialize child expressions
+	 * Initialize result slot, type and projection.
 	 */
-	scanstate->ss.ps.qual =
-		ExecInitQual(node->scan.plan.qual, (PlanState *) scanstate);
+	ExecInitResultTupleSlotTL(estate, &scanstate->ss.ps);
+	ExecAssignScanProjectionInfo(&scanstate->ss);
 
 	/*
-	 * get info about values list
+	 * initialize child expressions
 	 */
-	tupdesc = ExecTypeFromExprList((List *) linitial(node->values_lists));
-
-	ExecAssignScanType(&scanstate->ss, tupdesc);
+	scanstate->ss.ps.qual =
+		ExecInitQual(node->scan.plan.qual, (PlanState *) scanstate);
 
 	/*
 	 * Other node-specific setup
@@ -281,12 +280,6 @@ ExecInitValuesScan(ValuesScan *node, EState *estate, int eflags)
 		scanstate->exprlists[i++] = (List *) lfirst(vtl);
 	}
 
-	/*
-	 * Initialize result tuple type and projection info.
-	 */
-	ExecAssignResultTypeFromTL(&scanstate->ss.ps);
-	ExecAssignScanProjectionInfo(&scanstate->ss);
-
 	return scanstate;
 }