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, 26 insertions, 0 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 */