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, 14 insertions, 0 deletions

diff --git a/src/backend/executor/execProcnode.c b/src/backend/executor/execProcnode.c
index 284fc6a63b7..8ab9892c850 100644
--- a/src/backend/executor/execProcnode.c
+++ b/src/backend/executor/execProcnode.c
@@ -89,6 +89,7 @@
 #include "executor/nodeGroup.h"
 #include "executor/nodeHash.h"
 #include "executor/nodeHashjoin.h"
+#include "executor/nodeIndexonlyscan.h"
 #include "executor/nodeIndexscan.h"
 #include "executor/nodeLimit.h"
 #include "executor/nodeLockRows.h"
@@ -192,6 +193,11 @@ ExecInitNode(Plan *node, EState *estate, int eflags)
 													 estate, eflags);
 			break;
 
+		case T_IndexOnlyScan:
+			result = (PlanState *) ExecInitIndexOnlyScan((IndexOnlyScan *) node,
+														 estate, eflags);
+			break;
+
 		case T_BitmapIndexScan:
 			result = (PlanState *) ExecInitBitmapIndexScan((BitmapIndexScan *) node,
 														   estate, eflags);
@@ -397,6 +403,10 @@ ExecProcNode(PlanState *node)
 			result = ExecIndexScan((IndexScanState *) node);
 			break;
 
+		case T_IndexOnlyScanState:
+			result = ExecIndexOnlyScan((IndexOnlyScanState *) node);
+			break;
+
 			/* BitmapIndexScanState does not yield tuples */
 
 		case T_BitmapHeapScanState:
@@ -627,6 +637,10 @@ ExecEndNode(PlanState *node)
 			ExecEndIndexScan((IndexScanState *) node);
 			break;
 
+		case T_IndexOnlyScanState:
+			ExecEndIndexOnlyScan((IndexOnlyScanState *) node);
+			break;
+
 		case T_BitmapIndexScanState:
 			ExecEndBitmapIndexScan((BitmapIndexScanState *) node);
 			break;