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).

2 files changed, 31 insertions, 2 deletions

diff --git a/src/include/executor/nodeIndexonlyscan.h b/src/include/executor/nodeIndexonlyscan.h
new file mode 100644
index 00000000000..1c59cee5a73
--- /dev/null
+++ b/src/include/executor/nodeIndexonlyscan.h
@@ -0,0 +1,26 @@
+/*-------------------------------------------------------------------------
+ *
+ * nodeIndexonlyscan.h
+ *
+ *
+ *
+ * Portions Copyright (c) 1996-2011, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/executor/nodeIndexonlyscan.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef NODEINDEXONLYSCAN_H
+#define NODEINDEXONLYSCAN_H
+
+#include "nodes/execnodes.h"
+
+extern IndexOnlyScanState *ExecInitIndexOnlyScan(IndexOnlyScan *node, EState *estate, int eflags);
+extern TupleTableSlot *ExecIndexOnlyScan(IndexOnlyScanState *node);
+extern void ExecEndIndexOnlyScan(IndexOnlyScanState *node);
+extern void ExecIndexOnlyMarkPos(IndexOnlyScanState *node);
+extern void ExecIndexOnlyRestrPos(IndexOnlyScanState *node);
+extern void ExecReScanIndexOnlyScan(IndexOnlyScanState *node);
+
+#endif   /* NODEINDEXONLYSCAN_H */
diff --git a/src/include/executor/nodeIndexscan.h b/src/include/executor/nodeIndexscan.h
index 481a7df70fe..4094031c185 100644
--- a/src/include/executor/nodeIndexscan.h
+++ b/src/include/executor/nodeIndexscan.h
@@ -23,9 +23,12 @@ extern void ExecIndexMarkPos(IndexScanState *node);
 extern void ExecIndexRestrPos(IndexScanState *node);
 extern void ExecReScanIndexScan(IndexScanState *node);
 
-/* routines exported to share code with nodeBitmapIndexscan.c */
+/*
+ * These routines are exported to share code with nodeIndexonlyscan.c and
+ * nodeBitmapIndexscan.c
+ */
 extern void ExecIndexBuildScanKeys(PlanState *planstate, Relation index,
-					   Index scanrelid, List *quals, bool isorderby,
+					   List *quals, bool isorderby,
 					   ScanKey *scanKeys, int *numScanKeys,
 					   IndexRuntimeKeyInfo **runtimeKeys, int *numRuntimeKeys,
 					   IndexArrayKeyInfo **arrayKeys, int *numArrayKeys);