Rearrange the implementation of index-only scans.

This commit changes index-only scans so that data is read directly from the
index tuple without first generating a faux heap tuple.  The only immediate
benefit is that indexes on system columns (such as OID) can be used in
index-only scans, but this is necessary infrastructure if we are ever to
support index-only scans on expression indexes.  The executor is now ready
for that, though the planner still needs substantial work to recognize
the possibility.

To do this, Vars in index-only plan nodes have to refer to index columns
not heap columns.  I introduced a new special varno, INDEX_VAR, to mark
such Vars to avoid confusion.  (In passing, this commit renames the two
existing special varnos to OUTER_VAR and INNER_VAR.)  This allows
ruleutils.c to handle them with logic similar to what we use for subplan
reference Vars.

Since index-only scans are now fundamentally different from regular
indexscans so far as their expression subtrees are concerned, I also chose
to change them to have their own plan node type (and hence, their own
executor source file).

1 files changed, 4 insertions, 4 deletions

diff --git a/src/backend/commands/trigger.c b/src/backend/commands/trigger.c
index 06d368e0773..9fb97548485 100644
--- a/src/backend/commands/trigger.c
+++ b/src/backend/commands/trigger.c
@@ -2734,9 +2734,9 @@ TriggerEnabled(EState *estate, ResultRelInfo *relinfo,
 
 			oldContext = MemoryContextSwitchTo(estate->es_query_cxt);
 			tgqual = stringToNode(trigger->tgqual);
-			/* Change references to OLD and NEW to INNER and OUTER */
-			ChangeVarNodes(tgqual, PRS2_OLD_VARNO, INNER, 0);
-			ChangeVarNodes(tgqual, PRS2_NEW_VARNO, OUTER, 0);
+			/* Change references to OLD and NEW to INNER_VAR and OUTER_VAR */
+			ChangeVarNodes(tgqual, PRS2_OLD_VARNO, INNER_VAR, 0);
+			ChangeVarNodes(tgqual, PRS2_NEW_VARNO, OUTER_VAR, 0);
 			/* ExecQual wants implicit-AND form */
 			tgqual = (Node *) make_ands_implicit((Expr *) tgqual);
 			*predicate = (List *) ExecPrepareExpr((Expr *) tgqual, estate);
@@ -2783,7 +2783,7 @@ TriggerEnabled(EState *estate, ResultRelInfo *relinfo,
 
 		/*
 		 * Finally evaluate the expression, making the old and/or new tuples
-		 * available as INNER/OUTER respectively.
+		 * available as INNER_VAR/OUTER_VAR respectively.
 		 */
 		econtext->ecxt_innertuple = oldslot;
 		econtext->ecxt_outertuple = newslot;