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, 1 insertions, 1 deletions

diff --git a/src/backend/utils/adt/tid.c b/src/backend/utils/adt/tid.c
index 69e89b82c9e..b4ac9357fb4 100644
--- a/src/backend/utils/adt/tid.c
+++ b/src/backend/utils/adt/tid.c
@@ -306,7 +306,7 @@ currtid_for_view(Relation viewrel, ItemPointer tid)
 				Var		   *var = (Var *) tle->expr;
 				RangeTblEntry *rte;
 
-				if (var->varno > 0 && var->varno < INNER &&
+				if (!IS_SPECIAL_VARNO(var->varno) &&
 					var->varattno == SelfItemPointerAttributeNumber)
 				{
 					rte = rt_fetch(var->varno, query->rtable);