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, 20 insertions, 25 deletions

diff --git a/src/backend/executor/nodeIndexscan.c b/src/backend/executor/nodeIndexscan.c
index b8b961add4c..01c9de88f4d 100644
--- a/src/backend/executor/nodeIndexscan.c
+++ b/src/backend/executor/nodeIndexscan.c
@@ -941,6 +941,26 @@ ExecInitIndexScan(IndexScan *node, EState *estate, int eflags)
 	ExecAssignExprContext(estate, &indexstate->ss.ps);
 
 	/*
+	 * open the base relation and acquire appropriate lock on it.
+	 */
+	currentRelation = ExecOpenScanRelation(estate, node->scan.scanrelid, eflags);
+
+	indexstate->ss.ss_currentRelation = currentRelation;
+	indexstate->ss.ss_currentScanDesc = NULL;	/* no heap scan here */
+
+	/*
+	 * get the scan type from the relation descriptor.
+	 */
+	ExecInitScanTupleSlot(estate, &indexstate->ss,
+						  RelationGetDescr(currentRelation));
+
+	/*
+	 * Initialize result slot, type and projection.
+	 */
+	ExecInitResultTupleSlotTL(estate, &indexstate->ss.ps);
+	ExecAssignScanProjectionInfo(&indexstate->ss);
+
+	/*
 	 * initialize child expressions
 	 *
 	 * Note: we don't initialize all of the indexqual expression, only the
@@ -958,31 +978,6 @@ ExecInitIndexScan(IndexScan *node, EState *estate, int eflags)
 		ExecInitExprList(node->indexorderbyorig, (PlanState *) indexstate);
 
 	/*
-	 * tuple table initialization
-	 */
-	ExecInitResultTupleSlot(estate, &indexstate->ss.ps);
-	ExecInitScanTupleSlot(estate, &indexstate->ss);
-
-	/*
-	 * open the base relation and acquire appropriate lock on it.
-	 */
-	currentRelation = ExecOpenScanRelation(estate, node->scan.scanrelid, eflags);
-
-	indexstate->ss.ss_currentRelation = currentRelation;
-	indexstate->ss.ss_currentScanDesc = NULL;	/* no heap scan here */
-
-	/*
-	 * get the scan type from the relation descriptor.
-	 */
-	ExecAssignScanType(&indexstate->ss, RelationGetDescr(currentRelation));
-
-	/*
-	 * Initialize result tuple type and projection info.
-	 */
-	ExecAssignResultTypeFromTL(&indexstate->ss.ps);
-	ExecAssignScanProjectionInfo(&indexstate->ss);
-
-	/*
 	 * If we are just doing EXPLAIN (ie, aren't going to run the plan), stop
 	 * here.  This allows an index-advisor plugin to EXPLAIN a plan containing
 	 * references to nonexistent indexes.