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).

src/backend/commands/explain.c

@@ -79,6 +79,8 @@ static void show_instrumentation_count(const char *qlabel, int which,
 						   PlanState *planstate, ExplainState *es);
 static void show_foreignscan_info(ForeignScanState *fsstate, ExplainState *es);
 static const char *explain_get_index_name(Oid indexId);
+static void ExplainIndexScanDetails(Oid indexid, ScanDirection indexorderdir,
+						ExplainState *es);
 static void ExplainScanTarget(Scan *plan, ExplainState *es);
 static void ExplainModifyTarget(ModifyTable *plan, ExplainState *es);
 static void ExplainTargetRel(Plan *plan, Index rti, ExplainState *es);
@@ -656,10 +658,10 @@ ExplainNode(PlanState *planstate, List *ancestors,
 			pname = sname = "Seq Scan";
 			break;
 		case T_IndexScan:
-			if (((IndexScan *) plan)->indexonly)
-				pname = sname = "Index Only Scan";
-			else
-				pname = sname = "Index Scan";
+			pname = sname = "Index Scan";
+			break;
+		case T_IndexOnlyScan:
+			pname = sname = "Index Only Scan";
 			break;
 		case T_BitmapIndexScan:
 			pname = sname = "Bitmap Index Scan";
@@ -793,42 +795,6 @@ ExplainNode(PlanState *planstate, List *ancestors,
 
 	switch (nodeTag(plan))
 	{
-		case T_IndexScan:
-			{
-				IndexScan  *indexscan = (IndexScan *) plan;
-				const char *indexname =
-				explain_get_index_name(indexscan->indexid);
-
-				if (es->format == EXPLAIN_FORMAT_TEXT)
-				{
-					if (ScanDirectionIsBackward(indexscan->indexorderdir))
-						appendStringInfoString(es->str, " Backward");
-					appendStringInfo(es->str, " using %s", indexname);
-				}
-				else
-				{
-					const char *scandir;
-
-					switch (indexscan->indexorderdir)
-					{
-						case BackwardScanDirection:
-							scandir = "Backward";
-							break;
-						case NoMovementScanDirection:
-							scandir = "NoMovement";
-							break;
-						case ForwardScanDirection:
-							scandir = "Forward";
-							break;
-						default:
-							scandir = "???";
-							break;
-					}
-					ExplainPropertyText("Scan Direction", scandir, es);
-					ExplainPropertyText("Index Name", indexname, es);
-				}
-			}
-			/* FALL THRU */
 		case T_SeqScan:
 		case T_BitmapHeapScan:
 		case T_TidScan:
@@ -840,6 +806,26 @@ ExplainNode(PlanState *planstate, List *ancestors,
 		case T_ForeignScan:
 			ExplainScanTarget((Scan *) plan, es);
 			break;
+		case T_IndexScan:
+			{
+				IndexScan  *indexscan = (IndexScan *) plan;
+
+				ExplainIndexScanDetails(indexscan->indexid,
+										indexscan->indexorderdir,
+										es);
+				ExplainScanTarget((Scan *) indexscan, es);
+			}
+			break;
+		case T_IndexOnlyScan:
+			{
+				IndexOnlyScan *indexonlyscan = (IndexOnlyScan *) plan;
+
+				ExplainIndexScanDetails(indexonlyscan->indexid,
+										indexonlyscan->indexorderdir,
+										es);
+				ExplainScanTarget((Scan *) indexonlyscan, es);
+			}
+			break;
 		case T_BitmapIndexScan:
 			{
 				BitmapIndexScan *bitmapindexscan = (BitmapIndexScan *) plan;
@@ -1014,6 +1000,19 @@ ExplainNode(PlanState *planstate, List *ancestors,
 				show_instrumentation_count("Rows Removed by Filter", 1,
 										   planstate, es);
 			break;
+		case T_IndexOnlyScan:
+			show_scan_qual(((IndexOnlyScan *) plan)->indexqual,
+						   "Index Cond", planstate, ancestors, es);
+			if (((IndexOnlyScan *) plan)->indexqual)
+				show_instrumentation_count("Rows Removed by Index Recheck", 2,
+										   planstate, es);
+			show_scan_qual(((IndexOnlyScan *) plan)->indexorderby,
+						   "Order By", planstate, ancestors, es);
+			show_scan_qual(plan->qual, "Filter", planstate, ancestors, es);
+			if (plan->qual)
+				show_instrumentation_count("Rows Removed by Filter", 1,
+										   planstate, es);
+			break;
 		case T_BitmapIndexScan:
 			show_scan_qual(((BitmapIndexScan *) plan)->indexqualorig,
 						   "Index Cond", planstate, ancestors, es);
@@ -1626,6 +1625,45 @@ explain_get_index_name(Oid indexId)
 	return result;
 }
 
+/*
+ * Add some additional details about an IndexScan or IndexOnlyScan
+ */
+static void
+ExplainIndexScanDetails(Oid indexid, ScanDirection indexorderdir,
+						ExplainState *es)
+{
+	const char *indexname = explain_get_index_name(indexid);
+
+	if (es->format == EXPLAIN_FORMAT_TEXT)
+	{
+		if (ScanDirectionIsBackward(indexorderdir))
+			appendStringInfoString(es->str, " Backward");
+		appendStringInfo(es->str, " using %s", indexname);
+	}
+	else
+	{
+		const char *scandir;
+
+		switch (indexorderdir)
+		{
+			case BackwardScanDirection:
+				scandir = "Backward";
+				break;
+			case NoMovementScanDirection:
+				scandir = "NoMovement";
+				break;
+			case ForwardScanDirection:
+				scandir = "Forward";
+				break;
+			default:
+				scandir = "???";
+				break;
+		}
+		ExplainPropertyText("Scan Direction", scandir, es);
+		ExplainPropertyText("Index Name", indexname, es);
+	}
+}
+
 /*
  * Show the target of a Scan node
  */
@@ -1670,6 +1708,7 @@ ExplainTargetRel(Plan *plan, Index rti, ExplainState *es)
 	{
 		case T_SeqScan:
 		case T_IndexScan:
+		case T_IndexOnlyScan:
 		case T_BitmapHeapScan:
 		case T_TidScan:
 		case T_ForeignScan:

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;

src/backend/executor/Makefile

@@ -17,7 +17,8 @@ OBJS = execAmi.o execCurrent.o execGrouping.o execJunk.o execMain.o \
        execUtils.o functions.o instrument.o nodeAppend.o nodeAgg.o \
        nodeBitmapAnd.o nodeBitmapOr.o \
        nodeBitmapHeapscan.o nodeBitmapIndexscan.o nodeHash.o \
-       nodeHashjoin.o nodeIndexscan.o nodeLimit.o nodeLockRows.o \
+       nodeHashjoin.o nodeIndexscan.o nodeIndexonlyscan.o \
+       nodeLimit.o nodeLockRows.o \
        nodeMaterial.o nodeMergeAppend.o nodeMergejoin.o nodeModifyTable.o \
        nodeNestloop.o nodeFunctionscan.o nodeRecursiveunion.o nodeResult.o \
        nodeSeqscan.o nodeSetOp.o nodeSort.o nodeUnique.o \

src/backend/executor/execAmi.c

@@ -26,6 +26,7 @@
 #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"
@@ -155,6 +156,10 @@ ExecReScan(PlanState *node)
 			ExecReScanIndexScan((IndexScanState *) node);
 			break;
 
+		case T_IndexOnlyScanState:
+			ExecReScanIndexOnlyScan((IndexOnlyScanState *) node);
+			break;
+
 		case T_BitmapIndexScanState:
 			ExecReScanBitmapIndexScan((BitmapIndexScanState *) node);
 			break;
@@ -273,6 +278,10 @@ ExecMarkPos(PlanState *node)
 			ExecIndexMarkPos((IndexScanState *) node);
 			break;
 
+		case T_IndexOnlyScanState:
+			ExecIndexOnlyMarkPos((IndexOnlyScanState *) node);
+			break;
+
 		case T_TidScanState:
 			ExecTidMarkPos((TidScanState *) node);
 			break;
@@ -326,6 +335,10 @@ ExecRestrPos(PlanState *node)
 			ExecIndexRestrPos((IndexScanState *) node);
 			break;
 
+		case T_IndexOnlyScanState:
+			ExecIndexOnlyRestrPos((IndexOnlyScanState *) node);
+			break;
+
 		case T_TidScanState:
 			ExecTidRestrPos((TidScanState *) node);
 			break;
@@ -371,6 +384,7 @@ ExecSupportsMarkRestore(NodeTag plantype)
 	{
 		case T_SeqScan:
 		case T_IndexScan:
+		case T_IndexOnlyScan:
 		case T_TidScan:
 		case T_ValuesScan:
 		case T_Material:
@@ -442,6 +456,10 @@ ExecSupportsBackwardScan(Plan *node)
 			return IndexSupportsBackwardScan(((IndexScan *) node)->indexid) &&
 				TargetListSupportsBackwardScan(node->targetlist);
 
+		case T_IndexOnlyScan:
+			return IndexSupportsBackwardScan(((IndexOnlyScan *) node)->indexid) &&
+				TargetListSupportsBackwardScan(node->targetlist);
+
 		case T_SubqueryScan:
 			return ExecSupportsBackwardScan(((SubqueryScan *) node)->subplan) &&
 				TargetListSupportsBackwardScan(node->targetlist);
@@ -474,7 +492,8 @@ TargetListSupportsBackwardScan(List *targetlist)
 }
 
 /*
- * An IndexScan node supports backward scan only if the index's AM does.
+ * An IndexScan or IndexOnlyScan node supports backward scan only if the
+ * index's AM does.
  */
 static bool
 IndexSupportsBackwardScan(Oid indexid)

src/backend/executor/execCurrent.c

@@ -262,6 +262,7 @@ search_plan_tree(PlanState *node, Oid table_oid)
 			 */
 		case T_SeqScanState:
 		case T_IndexScanState:
+		case T_IndexOnlyScanState:
 		case T_BitmapHeapScanState:
 		case T_TidScanState:
 			{

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;

src/backend/executor/execQual.c

@@ -578,14 +578,16 @@ ExecEvalVar(ExprState *exprstate, ExprContext *econtext,
 	/* Get the input slot and attribute number we want */
 	switch (variable->varno)
 	{
-		case INNER:				/* get the tuple from the inner node */
+		case INNER_VAR:			/* get the tuple from the inner node */
 			slot = econtext->ecxt_innertuple;
 			break;
 
-		case OUTER:				/* get the tuple from the outer node */
+		case OUTER_VAR:			/* get the tuple from the outer node */
 			slot = econtext->ecxt_outertuple;
 			break;
 
+		/* INDEX_VAR is handled by default case */
+
 		default:				/* get the tuple from the relation being
 								 * scanned */
 			slot = econtext->ecxt_scantuple;
@@ -761,14 +763,16 @@ ExecEvalScalarVar(ExprState *exprstate, ExprContext *econtext,
 	/* Get the input slot and attribute number we want */
 	switch (variable->varno)
 	{
-		case INNER:				/* get the tuple from the inner node */
+		case INNER_VAR:			/* get the tuple from the inner node */
 			slot = econtext->ecxt_innertuple;
 			break;
 
-		case OUTER:				/* get the tuple from the outer node */
+		case OUTER_VAR:			/* get the tuple from the outer node */
 			slot = econtext->ecxt_outertuple;
 			break;
 
+		/* INDEX_VAR is handled by default case */
+
 		default:				/* get the tuple from the relation being
 								 * scanned */
 			slot = econtext->ecxt_scantuple;
@@ -804,14 +808,16 @@ ExecEvalWholeRowVar(ExprState *exprstate, ExprContext *econtext,
 	/* Get the input slot we want */
 	switch (variable->varno)
 	{
-		case INNER:				/* get the tuple from the inner node */
+		case INNER_VAR:			/* get the tuple from the inner node */
 			slot = econtext->ecxt_innertuple;
 			break;
 
-		case OUTER:				/* get the tuple from the outer node */
+		case OUTER_VAR:			/* get the tuple from the outer node */
 			slot = econtext->ecxt_outertuple;
 			break;
 
+		/* INDEX_VAR is handled by default case */
+
 		default:				/* get the tuple from the relation being
 								 * scanned */
 			slot = econtext->ecxt_scantuple;
@@ -873,14 +879,16 @@ ExecEvalWholeRowSlow(ExprState *exprstate, ExprContext *econtext,
 	/* Get the input slot we want */
 	switch (variable->varno)
 	{
-		case INNER:				/* get the tuple from the inner node */
+		case INNER_VAR:			/* get the tuple from the inner node */
 			slot = econtext->ecxt_innertuple;
 			break;
 
-		case OUTER:				/* get the tuple from the outer node */
+		case OUTER_VAR:			/* get the tuple from the outer node */
 			slot = econtext->ecxt_outertuple;
 			break;
 
+		/* INDEX_VAR is handled by default case */
+
 		default:				/* get the tuple from the relation being
 								 * scanned */
 			slot = econtext->ecxt_scantuple;

src/backend/executor/execScan.c

@@ -246,10 +246,17 @@ void
 ExecAssignScanProjectionInfo(ScanState *node)
 {
 	Scan	   *scan = (Scan *) node->ps.plan;
+	Index		varno;
+
+	/* Vars in an index-only scan's tlist should be INDEX_VAR */
+	if (IsA(scan, IndexOnlyScan))
+		varno = INDEX_VAR;
+	else
+		varno = scan->scanrelid;
 
 	if (tlist_matches_tupdesc(&node->ps,
 							  scan->plan.targetlist,
-							  scan->scanrelid,
+							  varno,
 							  node->ss_ScanTupleSlot->tts_tupleDescriptor))
 		node->ps.ps_ProjInfo = NULL;
 	else

src/backend/executor/execUtils.c

@@ -566,20 +566,22 @@ ExecBuildProjectionInfo(List *targetList,
 
 			switch (variable->varno)
 			{
-				case INNER:
+				case INNER_VAR:
 					varSlotOffsets[numSimpleVars] = offsetof(ExprContext,
 															 ecxt_innertuple);
 					if (projInfo->pi_lastInnerVar < attnum)
 						projInfo->pi_lastInnerVar = attnum;
 					break;
 
-				case OUTER:
+				case OUTER_VAR:
 					varSlotOffsets[numSimpleVars] = offsetof(ExprContext,
 															 ecxt_outertuple);
 					if (projInfo->pi_lastOuterVar < attnum)
 						projInfo->pi_lastOuterVar = attnum;
 					break;
 
+				/* INDEX_VAR is handled by default case */
+
 				default:
 					varSlotOffsets[numSimpleVars] = offsetof(ExprContext,
 															 ecxt_scantuple);
@@ -628,16 +630,18 @@ get_last_attnums(Node *node, ProjectionInfo *projInfo)
 
 		switch (variable->varno)
 		{
-			case INNER:
+			case INNER_VAR:
 				if (projInfo->pi_lastInnerVar < attnum)
 					projInfo->pi_lastInnerVar = attnum;
 				break;
 
-			case OUTER:
+			case OUTER_VAR:
 				if (projInfo->pi_lastOuterVar < attnum)
 					projInfo->pi_lastOuterVar = attnum;
 				break;
 
+			/* INDEX_VAR is handled by default case */
+
 			default:
 				if (projInfo->pi_lastScanVar < attnum)
 					projInfo->pi_lastScanVar = attnum;

src/backend/executor/nodeAgg.c

@@ -806,8 +806,8 @@ find_unaggregated_cols_walker(Node *node, Bitmapset **colnos)
 	{
 		Var		   *var = (Var *) node;
 
-		/* setrefs.c should have set the varno to OUTER */
-		Assert(var->varno == OUTER);
+		/* setrefs.c should have set the varno to OUTER_VAR */
+		Assert(var->varno == OUTER_VAR);
 		Assert(var->varlevelsup == 0);
 		*colnos = bms_add_member(*colnos, var->varattno);
 		return false;

src/backend/executor/nodeBitmapIndexscan.c

@@ -266,7 +266,6 @@ ExecInitBitmapIndexScan(BitmapIndexScan *node, EState *estate, int eflags)
 	 */
 	ExecIndexBuildScanKeys((PlanState *) indexstate,
 						   indexstate->biss_RelationDesc,
-						   node->scan.scanrelid,
 						   node->indexqual,
 						   false,
 						   &indexstate->biss_ScanKeys,

src/backend/executor/nodeHash.c

@@ -755,8 +755,8 @@ ExecHashTableInsert(HashJoinTable hashtable,
  *		Compute the hash value for a tuple
  *
  * The tuple to be tested must be in either econtext->ecxt_outertuple or
- * econtext->ecxt_innertuple.  Vars in the hashkeys expressions reference
- * either OUTER or INNER.
+ * econtext->ecxt_innertuple.  Vars in the hashkeys expressions should have
+ * varno either OUTER_VAR or INNER_VAR.
  *
  * A TRUE result means the tuple's hash value has been successfully computed
  * and stored at *hashvalue.  A FALSE result means the tuple cannot match

src/backend/executor/nodeIndexscan.c

@@ -14,8 +14,8 @@
  */
 /*
  * INTERFACE ROUTINES
- *		ExecIndexScan			scans a relation using indices
- *		ExecIndexNext			using index to retrieve next tuple
+ *		ExecIndexScan			scans a relation using an index
+ *		IndexNext				retrieve next tuple using index
  *		ExecInitIndexScan		creates and initializes state info.
  *		ExecReScanIndexScan		rescans the indexed relation.
  *		ExecEndIndexScan		releases all storage.
@@ -26,7 +26,6 @@
 
 #include "access/nbtree.h"
 #include "access/relscan.h"
-#include "access/visibilitymap.h"
 #include "executor/execdebug.h"
 #include "executor/nodeIndexscan.h"
 #include "optimizer/clauses.h"
@@ -37,7 +36,6 @@
 
 
 static TupleTableSlot *IndexNext(IndexScanState *node);
-static void IndexStoreHeapTuple(TupleTableSlot *slot, IndexScanDesc scandesc);
 
 
 /* ----------------------------------------------------------------
@@ -56,7 +54,6 @@ IndexNext(IndexScanState *node)
 	IndexScanDesc scandesc;
 	HeapTuple	tuple;
 	TupleTableSlot *slot;
-	ItemPointer tid;
 
 	/*
 	 * extract necessary information from index scan node
@@ -76,67 +73,23 @@ IndexNext(IndexScanState *node)
 	slot = node->ss.ss_ScanTupleSlot;
 
 	/*
-	 * OK, now that we have what we need, fetch the next TID.
+	 * ok, now that we have what we need, fetch the next tuple.
 	 */
-	while ((tid = index_getnext_tid(scandesc, direction)) != NULL)
+	while ((tuple = index_getnext(scandesc, direction)) != NULL)
 	{
 		/*
-		 * Attempt index-only scan, if possible.  For this, we need to have
-		 * gotten an index tuple from the AM, and we need the TID to reference
-		 * a heap page on which all tuples are known visible to everybody.
-		 * If that's the case, we don't need to visit the heap page for tuple
-		 * visibility testing, and we don't need any column values that are
-		 * not available from the index.
-		 *
-		 * Note: in the index-only path, we are still holding pin on the
-		 * scan's xs_cbuf, ie, the previously visited heap page.  It's not
-		 * clear whether it'd be better to release that pin.
+		 * Store the scanned tuple in the scan tuple slot of the scan state.
+		 * Note: we pass 'false' because tuples returned by amgetnext are
+		 * pointers onto disk pages and must not be pfree()'d.
 		 */
-		if (scandesc->xs_want_itup &&
-			visibilitymap_test(scandesc->heapRelation,
-							   ItemPointerGetBlockNumber(tid),
-							   &node->iss_VMBuffer))
-		{
-			/*
-			 * Convert index tuple to look like a heap tuple, and store the
-			 * results in the scan tuple slot.
-			 */
-			IndexStoreHeapTuple(slot, scandesc);
-		}
-		else
-		{
-			/* Index-only approach not possible, so fetch heap tuple. */
-			tuple = index_fetch_heap(scandesc);
-
-			/* Tuple might not be visible. */
-			if (tuple == NULL)
-				continue;
-
-			/*
-			 * Only MVCC snapshots are supported here, so there should be no
-			 * need to keep following the HOT chain once a visible entry has
-			 * been found.  If we did want to allow that, we'd need to keep
-			 * more state to remember not to call index_getnext_tid next time.
-			 */
-			if (scandesc->xs_continue_hot)
-				elog(ERROR, "unsupported use of non-MVCC snapshot in executor");
-
-			/*
-			 * Store the scanned tuple in the scan tuple slot of the scan
-			 * state.
-			 *
-			 * Note: we pass 'false' because tuples returned by amgetnext are
-			 * pointers onto disk pages and must not be pfree()'d.
-			 */
-			ExecStoreTuple(tuple,	/* tuple to store */
-						   slot,	/* slot to store in */
-						   scandesc->xs_cbuf,	/* buffer containing tuple */
-						   false);	/* don't pfree */
-		}
+		ExecStoreTuple(tuple,	/* tuple to store */
+					   slot,	/* slot to store in */
+					   scandesc->xs_cbuf,		/* buffer containing tuple */
+					   false);	/* don't pfree */
 
 		/*
 		 * If the index was lossy, we have to recheck the index quals using
-		 * the real tuple.
+		 * the fetched tuple.
 		 */
 		if (scandesc->xs_recheck)
 		{
@@ -160,53 +113,6 @@ IndexNext(IndexScanState *node)
 	return ExecClearTuple(slot);
 }
 
-/*
- * IndexStoreHeapTuple
- *
- *		When performing an index-only scan, we build a faux heap tuple
- *		from the index tuple.  Columns not present in the index are set to
- *		NULL, which is OK because we know they won't be referenced.
- *
- *		The faux tuple is built as a virtual tuple that depends on the
- *		scandesc's xs_itup, so that must remain valid for as long as we
- *		need the slot contents.
- */
-static void
-IndexStoreHeapTuple(TupleTableSlot *slot, IndexScanDesc scandesc)
-{
-	Form_pg_index indexForm = scandesc->indexRelation->rd_index;
-	TupleDesc	indexDesc = RelationGetDescr(scandesc->indexRelation);
-	int			nindexatts = indexDesc->natts;
-	int			nheapatts = slot->tts_tupleDescriptor->natts;
-	Datum	   *values = slot->tts_values;
-	bool	   *isnull = slot->tts_isnull;
-	int			i;
-
-	/* We must first set the slot to empty, and mark all columns as null */
-	ExecClearTuple(slot);
-
-	memset(isnull, true, nheapatts * sizeof(bool));
-
-	/* Transpose index tuple into heap tuple. */
-	for (i = 0; i < nindexatts; i++)
-	{
-		int		indexatt = indexForm->indkey.values[i];
-
-		/* Ignore expression columns, as well as system attributes */
-		if (indexatt <= 0)
-			continue;
-
-		Assert(indexatt <= nheapatts);
-
-		values[indexatt - 1] = index_getattr(scandesc->xs_itup, i + 1,
-											 indexDesc,
-											 &isnull[indexatt - 1]);
-	}
-
-	/* And now we can mark the slot as holding a virtual tuple. */
-	ExecStoreVirtualTuple(slot);
-}
-
 /*
  * IndexRecheck -- access method routine to recheck a tuple in EvalPlanQual
  */
@@ -493,13 +399,6 @@ ExecEndIndexScan(IndexScanState *node)
 	indexScanDesc = node->iss_ScanDesc;
 	relation = node->ss.ss_currentRelation;
 
-	/* Release VM buffer pin, if any. */
-	if (node->iss_VMBuffer != InvalidBuffer)
-	{
-		ReleaseBuffer(node->iss_VMBuffer);
-		node->iss_VMBuffer = InvalidBuffer;
-	}
-
 	/*
 	 * Free the exprcontext(s) ... now dead code, see ExecFreeExprContext
 	 */
@@ -659,7 +558,6 @@ ExecInitIndexScan(IndexScan *node, EState *estate, int eflags)
 	 */
 	ExecIndexBuildScanKeys((PlanState *) indexstate,
 						   indexstate->iss_RelationDesc,
-						   node->scan.scanrelid,
 						   node->indexqual,
 						   false,
 						   &indexstate->iss_ScanKeys,
@@ -674,7 +572,6 @@ ExecInitIndexScan(IndexScan *node, EState *estate, int eflags)
 	 */
 	ExecIndexBuildScanKeys((PlanState *) indexstate,
 						   indexstate->iss_RelationDesc,
-						   node->scan.scanrelid,
 						   node->indexorderby,
 						   true,
 						   &indexstate->iss_OrderByKeys,
@@ -712,10 +609,6 @@ ExecInitIndexScan(IndexScan *node, EState *estate, int eflags)
 											   indexstate->iss_NumScanKeys,
 											 indexstate->iss_NumOrderByKeys);
 
-	/* Prepare for possible index-only scan */
-	indexstate->iss_ScanDesc->xs_want_itup = node->indexonly;
-	indexstate->iss_VMBuffer = InvalidBuffer;
-
 	/*
 	 * If no run-time keys to calculate, go ahead and pass the scankeys to the
 	 * index AM.
@@ -772,7 +665,6 @@ ExecInitIndexScan(IndexScan *node, EState *estate, int eflags)
  *
  * planstate: executor state node we are working for
  * index: the index we are building scan keys for
- * scanrelid: varno of the index's relation within current query
  * quals: indexquals (or indexorderbys) expressions
  * isorderby: true if processing ORDER BY exprs, false if processing quals
  * *runtimeKeys: ptr to pre-existing IndexRuntimeKeyInfos, or NULL if none
@@ -791,7 +683,7 @@ ExecInitIndexScan(IndexScan *node, EState *estate, int eflags)
  * ScalarArrayOpExpr quals are not supported.
  */
 void
-ExecIndexBuildScanKeys(PlanState *planstate, Relation index, Index scanrelid,
+ExecIndexBuildScanKeys(PlanState *planstate, Relation index,
 					   List *quals, bool isorderby,
 					   ScanKey *scanKeys, int *numScanKeys,
 					   IndexRuntimeKeyInfo **runtimeKeys, int *numRuntimeKeys,
@@ -865,7 +757,7 @@ ExecIndexBuildScanKeys(PlanState *planstate, Relation index, Index scanrelid,
 			Assert(leftop != NULL);
 
 			if (!(IsA(leftop, Var) &&
-				  ((Var *) leftop)->varno == scanrelid))
+				  ((Var *) leftop)->varno == INDEX_VAR))
 				elog(ERROR, "indexqual doesn't have key on left side");
 
 			varattno = ((Var *) leftop)->varattno;
@@ -979,7 +871,7 @@ ExecIndexBuildScanKeys(PlanState *planstate, Relation index, Index scanrelid,
 				Assert(leftop != NULL);
 
 				if (!(IsA(leftop, Var) &&
-					  ((Var *) leftop)->varno == scanrelid))
+					  ((Var *) leftop)->varno == INDEX_VAR))
 					elog(ERROR, "indexqual doesn't have key on left side");
 
 				varattno = ((Var *) leftop)->varattno;
@@ -1107,7 +999,7 @@ ExecIndexBuildScanKeys(PlanState *planstate, Relation index, Index scanrelid,
 			Assert(leftop != NULL);
 
 			if (!(IsA(leftop, Var) &&
-				  ((Var *) leftop)->varno == scanrelid))
+				  ((Var *) leftop)->varno == INDEX_VAR))
 				elog(ERROR, "indexqual doesn't have key on left side");
 
 			varattno = ((Var *) leftop)->varattno;
@@ -1172,7 +1064,7 @@ ExecIndexBuildScanKeys(PlanState *planstate, Relation index, Index scanrelid,
 			Assert(leftop != NULL);
 
 			if (!(IsA(leftop, Var) &&
-				  ((Var *) leftop)->varno == scanrelid))
+				  ((Var *) leftop)->varno == INDEX_VAR))
 				elog(ERROR, "NullTest indexqual has wrong key");
 
 			varattno = ((Var *) leftop)->varattno;

src/backend/executor/nodeNestloop.c

@@ -147,8 +147,8 @@ ExecNestLoop(NestLoopState *node)
 				ParamExecData *prm;
 
 				prm = &(econtext->ecxt_param_exec_vals[paramno]);
-				/* Param value should be an OUTER var */
-				Assert(nlp->paramval->varno == OUTER);
+				/* Param value should be an OUTER_VAR var */
+				Assert(nlp->paramval->varno == OUTER_VAR);
 				Assert(nlp->paramval->varattno > 0);
 				prm->value = slot_getattr(outerTupleSlot,
 										  nlp->paramval->varattno,

src/backend/nodes/copyfuncs.c

@@ -370,7 +370,31 @@ _copyIndexScan(IndexScan *from)
 	COPY_NODE_FIELD(indexorderby);
 	COPY_NODE_FIELD(indexorderbyorig);
 	COPY_SCALAR_FIELD(indexorderdir);
-	COPY_SCALAR_FIELD(indexonly);
+
+	return newnode;
+}
+
+/*
+ * _copyIndexOnlyScan
+ */
+static IndexOnlyScan *
+_copyIndexOnlyScan(IndexOnlyScan *from)
+{
+	IndexOnlyScan  *newnode = makeNode(IndexOnlyScan);
+
+	/*
+	 * copy node superclass fields
+	 */
+	CopyScanFields((Scan *) from, (Scan *) newnode);
+
+	/*
+	 * copy remainder of node
+	 */
+	COPY_SCALAR_FIELD(indexid);
+	COPY_NODE_FIELD(indexqual);
+	COPY_NODE_FIELD(indexorderby);
+	COPY_NODE_FIELD(indextlist);
+	COPY_SCALAR_FIELD(indexorderdir);
 
 	return newnode;
 }
@@ -3871,6 +3895,9 @@ copyObject(void *from)
 		case T_IndexScan:
 			retval = _copyIndexScan(from);
 			break;
+		case T_IndexOnlyScan:
+			retval = _copyIndexOnlyScan(from);
+			break;
 		case T_BitmapIndexScan:
 			retval = _copyBitmapIndexScan(from);
 			break;

src/backend/nodes/outfuncs.c

@@ -447,7 +447,20 @@ _outIndexScan(StringInfo str, IndexScan *node)
 	WRITE_NODE_FIELD(indexorderby);
 	WRITE_NODE_FIELD(indexorderbyorig);
 	WRITE_ENUM_FIELD(indexorderdir, ScanDirection);
-	WRITE_BOOL_FIELD(indexonly);
+}
+
+static void
+_outIndexOnlyScan(StringInfo str, IndexOnlyScan *node)
+{
+	WRITE_NODE_TYPE("INDEXONLYSCAN");
+
+	_outScanInfo(str, (Scan *) node);
+
+	WRITE_OID_FIELD(indexid);
+	WRITE_NODE_FIELD(indexqual);
+	WRITE_NODE_FIELD(indexorderby);
+	WRITE_NODE_FIELD(indextlist);
+	WRITE_ENUM_FIELD(indexorderdir, ScanDirection);
 }
 
 static void
@@ -1501,7 +1514,6 @@ _outIndexPath(StringInfo str, IndexPath *node)
 	WRITE_NODE_FIELD(indexorderbys);
 	WRITE_BOOL_FIELD(isjoininner);
 	WRITE_ENUM_FIELD(indexscandir, ScanDirection);
-	WRITE_BOOL_FIELD(indexonly);
 	WRITE_FLOAT_FIELD(indextotalcost, "%.2f");
 	WRITE_FLOAT_FIELD(indexselectivity, "%.4f");
 	WRITE_FLOAT_FIELD(rows, "%.0f");
@@ -1752,8 +1764,9 @@ _outIndexOptInfo(StringInfo str, IndexOptInfo *node)
 	WRITE_FLOAT_FIELD(tuples, "%.0f");
 	WRITE_INT_FIELD(ncolumns);
 	WRITE_OID_FIELD(relam);
-	WRITE_NODE_FIELD(indexprs);
+	/* indexprs is redundant since we print indextlist */
 	WRITE_NODE_FIELD(indpred);
+	WRITE_NODE_FIELD(indextlist);
 	WRITE_BOOL_FIELD(predOK);
 	WRITE_BOOL_FIELD(unique);
 	WRITE_BOOL_FIELD(hypothetical);
@@ -2707,6 +2720,9 @@ _outNode(StringInfo str, void *obj)
 			case T_IndexScan:
 				_outIndexScan(str, obj);
 				break;
+			case T_IndexOnlyScan:
+				_outIndexOnlyScan(str, obj);
+				break;
 			case T_BitmapIndexScan:
 				_outBitmapIndexScan(str, obj);
 				break;

src/backend/nodes/print.c

@@ -320,14 +320,18 @@ print_expr(Node *expr, List *rtable)
 
 		switch (var->varno)
 		{
-			case INNER:
+			case INNER_VAR:
 				relname = "INNER";
 				attname = "?";
 				break;
-			case OUTER:
+			case OUTER_VAR:
 				relname = "OUTER";
 				attname = "?";
 				break;
+			case INDEX_VAR:
+				relname = "INDEX";
+				attname = "?";
+				break;
 			default:
 				{
 					RangeTblEntry *rte;

src/backend/optimizer/path/indxpath.c

@@ -199,14 +199,15 @@ create_index_paths(PlannerInfo *root, RelOptInfo *rel)
 									 true, NULL, SAOP_FORBID, ST_ANYSCAN);
 
 	/*
-	 * Submit all the ones that can form plain IndexScan plans to add_path. (A
-	 * plain IndexPath always represents a plain IndexScan plan; however some
-	 * of the indexes might support only bitmap scans, and those we mustn't
-	 * submit to add_path here.)  Also, pick out the ones that might be useful
-	 * as bitmap scans.  For that, we must discard indexes that don't support
-	 * bitmap scans, and we also are only interested in paths that have some
-	 * selectivity; we should discard anything that was generated solely for
-	 * ordering purposes.
+	 * Submit all the ones that can form plain IndexScan plans to add_path.
+	 * (A plain IndexPath might represent either a plain IndexScan or an
+	 * IndexOnlyScan, but for our purposes here the distinction does not
+	 * matter.  However, some of the indexes might support only bitmap scans,
+	 * and those we mustn't submit to add_path here.)  Also, pick out the ones
+	 * that might be useful as bitmap scans.  For that, we must discard
+	 * indexes that don't support bitmap scans, and we also are only
+	 * interested in paths that have some selectivity; we should discard
+	 * anything that was generated solely for ordering purposes.
 	 */
 	bitindexpaths = NIL;
 	foreach(l, indexpaths)
@@ -1107,11 +1108,9 @@ check_index_only(RelOptInfo *rel, IndexOptInfo *index)
 
 		/*
 		 * For the moment, we just ignore index expressions.  It might be nice
-		 * to do something with them, later.  We also ignore index columns
-		 * that are system columns (such as OID), because the virtual-tuple
-		 * coding used by IndexStoreHeapTuple() can't deal with them.
+		 * to do something with them, later.
 		 */
-		if (attno <= 0)
+		if (attno == 0)
 			continue;
 
 		index_attrs =

src/backend/optimizer/path/pathkeys.c

@@ -25,7 +25,6 @@
 #include "optimizer/pathnode.h"
 #include "optimizer/paths.h"
 #include "optimizer/tlist.h"
-#include "parser/parsetree.h"
 #include "utils/lsyscache.h"
 
 
@@ -35,8 +34,6 @@ static PathKey *make_canonical_pathkey(PlannerInfo *root,
 					   EquivalenceClass *eclass, Oid opfamily,
 					   int strategy, bool nulls_first);
 static bool pathkey_is_redundant(PathKey *new_pathkey, List *pathkeys);
-static Var *find_indexkey_var(PlannerInfo *root, RelOptInfo *rel,
-				  AttrNumber varattno);
 static bool right_merge_direction(PlannerInfo *root, PathKey *pathkey);
 
 
@@ -504,21 +501,24 @@ build_index_pathkeys(PlannerInfo *root,
 					 ScanDirection scandir)
 {
 	List	   *retval = NIL;
-	ListCell   *indexprs_item;
+	ListCell   *lc;
 	int			i;
 
 	if (index->sortopfamily == NULL)
 		return NIL;				/* non-orderable index */
 
-	indexprs_item = list_head(index->indexprs);
-	for (i = 0; i < index->ncolumns; i++)
+	i = 0;
+	foreach(lc, index->indextlist)
 	{
+		TargetEntry *indextle = (TargetEntry *) lfirst(lc);
+		Expr	   *indexkey;
 		bool		reverse_sort;
 		bool		nulls_first;
-		int			ikey;
-		Expr	   *indexkey;
 		PathKey    *cpathkey;
 
+		/* We assume we don't need to make a copy of the tlist item */
+		indexkey = indextle->expr;
+
 		if (ScanDirectionIsBackward(scandir))
 		{
 			reverse_sort = !index->reverse_sort[i];
@@ -530,21 +530,6 @@ build_index_pathkeys(PlannerInfo *root,
 			nulls_first = index->nulls_first[i];
 		}
 
-		ikey = index->indexkeys[i];
-		if (ikey != 0)
-		{
-			/* simple index column */
-			indexkey = (Expr *) find_indexkey_var(root, index->rel, ikey);
-		}
-		else
-		{
-			/* expression --- assume we need not copy it */
-			if (indexprs_item == NULL)
-				elog(ERROR, "wrong number of index expressions");
-			indexkey = (Expr *) lfirst(indexprs_item);
-			indexprs_item = lnext(indexprs_item);
-		}
-
 		/* OK, try to make a canonical pathkey for this sort key */
 		cpathkey = make_pathkey_from_sortinfo(root,
 											  indexkey,
@@ -568,44 +553,11 @@ build_index_pathkeys(PlannerInfo *root,
 		/* Add to list unless redundant */
 		if (!pathkey_is_redundant(cpathkey, retval))
 			retval = lappend(retval, cpathkey);
-	}
 
-	return retval;
-}
-
-/*
- * Find or make a Var node for the specified attribute of the rel.
- *
- * We first look for the var in the rel's target list, because that's
- * easy and fast.  But the var might not be there (this should normally
- * only happen for vars that are used in WHERE restriction clauses,
- * but not in join clauses or in the SELECT target list).  In that case,
- * gin up a Var node the hard way.
- */
-static Var *
-find_indexkey_var(PlannerInfo *root, RelOptInfo *rel, AttrNumber varattno)
-{
-	ListCell   *temp;
-	Index		relid;
-	Oid			reloid,
-				vartypeid,
-				varcollid;
-	int32		type_mod;
-
-	foreach(temp, rel->reltargetlist)
-	{
-		Var		   *var = (Var *) lfirst(temp);
-
-		if (IsA(var, Var) &&
-			var->varattno == varattno)
-			return var;
+		i++;
 	}
 
-	relid = rel->relid;
-	reloid = getrelid(relid, root->parse->rtable);
-	get_atttypetypmodcoll(reloid, varattno, &vartypeid, &type_mod, &varcollid);
-
-	return makeVar(relid, varattno, vartypeid, type_mod, varcollid, 0);
+	return retval;
 }
 
 /*

src/backend/optimizer/plan/createplan.c

@@ -53,8 +53,8 @@ static Material *create_material_plan(PlannerInfo *root, MaterialPath *best_path
 static Plan *create_unique_plan(PlannerInfo *root, UniquePath *best_path);
 static SeqScan *create_seqscan_plan(PlannerInfo *root, Path *best_path,
 					List *tlist, List *scan_clauses);
-static IndexScan *create_indexscan_plan(PlannerInfo *root, IndexPath *best_path,
-					  List *tlist, List *scan_clauses);
+static Scan *create_indexscan_plan(PlannerInfo *root, IndexPath *best_path,
+					  List *tlist, List *scan_clauses, bool indexonly);
 static BitmapHeapScan *create_bitmap_scan_plan(PlannerInfo *root,
 						BitmapHeapPath *best_path,
 						List *tlist, List *scan_clauses);
@@ -95,7 +95,12 @@ static SeqScan *make_seqscan(List *qptlist, List *qpqual, Index scanrelid);
 static IndexScan *make_indexscan(List *qptlist, List *qpqual, Index scanrelid,
 			   Oid indexid, List *indexqual, List *indexqualorig,
 			   List *indexorderby, List *indexorderbyorig,
-			   ScanDirection indexscandir, bool indexonly);
+			   ScanDirection indexscandir);
+static IndexOnlyScan *make_indexonlyscan(List *qptlist, List *qpqual,
+				   Index scanrelid, Oid indexid,
+				   List *indexqual, List *indexorderby,
+				   List *indextlist,
+				   ScanDirection indexscandir);
 static BitmapIndexScan *make_bitmap_indexscan(Index scanrelid, Oid indexid,
 					  List *indexqual,
 					  List *indexqualorig);
@@ -206,6 +211,7 @@ create_plan_recurse(PlannerInfo *root, Path *best_path)
 	{
 		case T_SeqScan:
 		case T_IndexScan:
+		case T_IndexOnlyScan:
 		case T_BitmapHeapScan:
 		case T_TidScan:
 		case T_SubqueryScan:
@@ -274,10 +280,18 @@ create_scan_plan(PlannerInfo *root, Path *best_path)
 	 */
 	if (use_physical_tlist(root, rel))
 	{
-		tlist = build_physical_tlist(root, rel);
-		/* if fail because of dropped cols, use regular method */
-		if (tlist == NIL)
-			tlist = build_relation_tlist(rel);
+		if (best_path->pathtype == T_IndexOnlyScan)
+		{
+			/* For index-only scan, the preferred tlist is the index's */
+			tlist = copyObject(((IndexPath *) best_path)->indexinfo->indextlist);
+		}
+		else
+		{
+			tlist = build_physical_tlist(root, rel);
+			/* if fail because of dropped cols, use regular method */
+			if (tlist == NIL)
+				tlist = build_relation_tlist(rel);
+		}
 	}
 	else
 		tlist = build_relation_tlist(rel);
@@ -302,7 +316,16 @@ create_scan_plan(PlannerInfo *root, Path *best_path)
 			plan = (Plan *) create_indexscan_plan(root,
 												  (IndexPath *) best_path,
 												  tlist,
-												  scan_clauses);
+												  scan_clauses,
+												  false);
+			break;
+
+		case T_IndexOnlyScan:
+			plan = (Plan *) create_indexscan_plan(root,
+												  (IndexPath *) best_path,
+												  tlist,
+												  scan_clauses,
+												  true);
 			break;
 
 		case T_BitmapHeapScan:
@@ -476,6 +499,7 @@ disuse_physical_tlist(Plan *plan, Path *path)
 	{
 		case T_SeqScan:
 		case T_IndexScan:
+		case T_IndexOnlyScan:
 		case T_BitmapHeapScan:
 		case T_TidScan:
 		case T_SubqueryScan:
@@ -1044,16 +1068,23 @@ create_seqscan_plan(PlannerInfo *root, Path *best_path,
  *	  Returns an indexscan plan for the base relation scanned by 'best_path'
  *	  with restriction clauses 'scan_clauses' and targetlist 'tlist'.
  *
+ * We use this for both plain IndexScans and IndexOnlyScans, because the
+ * qual preprocessing work is the same for both.  Note that the caller tells
+ * us which to build --- we don't look at best_path->path.pathtype, because
+ * create_bitmap_subplan needs to be able to override the prior decision.
+ *
  * The indexquals list of the path contains implicitly-ANDed qual conditions.
  * The list can be empty --- then no index restrictions will be applied during
  * the scan.
  */
-static IndexScan *
+static Scan *
 create_indexscan_plan(PlannerInfo *root,
 					  IndexPath *best_path,
 					  List *tlist,
-					  List *scan_clauses)
+					  List *scan_clauses,
+					  bool indexonly)
 {
+	Scan	   *scan_plan;
 	List	   *indexquals = best_path->indexquals;
 	List	   *indexorderbys = best_path->indexorderbys;
 	Index		baserelid = best_path->path.parent->relid;
@@ -1063,7 +1094,6 @@ create_indexscan_plan(PlannerInfo *root,
 	List	   *fixed_indexquals;
 	List	   *fixed_indexorderbys;
 	ListCell   *l;
-	IndexScan  *scan_plan;
 
 	/* it should be a base rel... */
 	Assert(baserelid > 0);
@@ -1077,7 +1107,7 @@ create_indexscan_plan(PlannerInfo *root,
 
 	/*
 	 * The executor needs a copy with the indexkey on the left of each clause
-	 * and with index attr numbers substituted for table ones.
+	 * and with index Vars substituted for table ones.
 	 */
 	fixed_indexquals = fix_indexqual_references(root, best_path, indexquals);
 
@@ -1175,20 +1205,29 @@ create_indexscan_plan(PlannerInfo *root,
 	}
 
 	/* Finally ready to build the plan node */
-	scan_plan = make_indexscan(tlist,
-							   qpqual,
-							   baserelid,
-							   indexoid,
-							   fixed_indexquals,
-							   stripped_indexquals,
-							   fixed_indexorderbys,
-							   indexorderbys,
-							   best_path->indexscandir,
-							   best_path->indexonly);
-
-	copy_path_costsize(&scan_plan->scan.plan, &best_path->path);
+	if (indexonly)
+		scan_plan = (Scan *) make_indexonlyscan(tlist,
+												qpqual,
+												baserelid,
+												indexoid,
+												fixed_indexquals,
+												fixed_indexorderbys,
+												best_path->indexinfo->indextlist,
+												best_path->indexscandir);
+	else
+		scan_plan = (Scan *) make_indexscan(tlist,
+											qpqual,
+											baserelid,
+											indexoid,
+											fixed_indexquals,
+											stripped_indexquals,
+											fixed_indexorderbys,
+											indexorderbys,
+											best_path->indexscandir);
+
+	copy_path_costsize(&scan_plan->plan, &best_path->path);
 	/* use the indexscan-specific rows estimate, not the parent rel's */
-	scan_plan->scan.plan.plan_rows = best_path->rows;
+	scan_plan->plan.plan_rows = best_path->rows;
 
 	return scan_plan;
 }
@@ -1440,7 +1479,9 @@ create_bitmap_subplan(PlannerInfo *root, Path *bitmapqual,
 		ListCell   *l;
 
 		/* Use the regular indexscan plan build machinery... */
-		iscan = create_indexscan_plan(root, ipath, NIL, NIL);
+		iscan = (IndexScan *) create_indexscan_plan(root, ipath,
+													NIL, NIL, false);
+		Assert(IsA(iscan, IndexScan));
 		/* then convert to a bitmap indexscan */
 		plan = (Plan *) make_bitmap_indexscan(iscan->scan.scanrelid,
 											  iscan->indexid,
@@ -2549,17 +2590,13 @@ fix_indexorderby_references(PlannerInfo *root, IndexPath *index_path,
 /*
  * fix_indexqual_operand
  *	  Convert an indexqual expression to a Var referencing the index column.
+ *
+ * We represent index keys by Var nodes having varno == INDEX_VAR and varattno
+ * equal to the index's attribute number (index column position).
  */
 static Node *
 fix_indexqual_operand(Node *node, IndexOptInfo *index)
 {
-	/*
-	 * We represent index keys by Var nodes having the varno of the base table
-	 * but varattno equal to the index's attribute number (index column
-	 * position).  This is a bit hokey ... would be cleaner to use a
-	 * special-purpose node type that could not be mistaken for a regular Var.
-	 * But it will do for now.
-	 */
 	Var		   *result;
 	int			pos;
 	ListCell   *indexpr_item;
@@ -2583,6 +2620,7 @@ fix_indexqual_operand(Node *node, IndexOptInfo *index)
 				if (index->indexkeys[pos] == varatt)
 				{
 					result = (Var *) copyObject(node);
+					result->varno = INDEX_VAR;
 					result->varattno = pos + 1;
 					return (Node *) result;
 				}
@@ -2606,7 +2644,7 @@ fix_indexqual_operand(Node *node, IndexOptInfo *index)
 			if (equal(node, indexkey))
 			{
 				/* Found a match */
-				result = makeVar(index->rel->relid, pos + 1,
+				result = makeVar(INDEX_VAR, pos + 1,
 								 exprType(lfirst(indexpr_item)), -1,
 								 exprCollation(lfirst(indexpr_item)),
 								 0);
@@ -2842,8 +2880,7 @@ make_indexscan(List *qptlist,
 			   List *indexqualorig,
 			   List *indexorderby,
 			   List *indexorderbyorig,
-			   ScanDirection indexscandir,
-			   bool indexonly)
+			   ScanDirection indexscandir)
 {
 	IndexScan  *node = makeNode(IndexScan);
 	Plan	   *plan = &node->scan.plan;
@@ -2860,7 +2897,34 @@ make_indexscan(List *qptlist,
 	node->indexorderby = indexorderby;
 	node->indexorderbyorig = indexorderbyorig;
 	node->indexorderdir = indexscandir;
-	node->indexonly = indexonly;
+
+	return node;
+}
+
+static IndexOnlyScan *
+make_indexonlyscan(List *qptlist,
+				   List *qpqual,
+				   Index scanrelid,
+				   Oid indexid,
+				   List *indexqual,
+				   List *indexorderby,
+				   List *indextlist,
+				   ScanDirection indexscandir)
+{
+	IndexOnlyScan *node = makeNode(IndexOnlyScan);
+	Plan	   *plan = &node->scan.plan;
+
+	/* cost should be inserted by caller */
+	plan->targetlist = qptlist;
+	plan->qual = qpqual;
+	plan->lefttree = NULL;
+	plan->righttree = NULL;
+	node->scan.scanrelid = scanrelid;
+	node->indexid = indexid;
+	node->indexqual = indexqual;
+	node->indexorderby = indexorderby;
+	node->indextlist = indextlist;
+	node->indexorderdir = indexscandir;
 
 	return node;
 }

src/backend/optimizer/plan/subselect.c

@@ -1974,6 +1974,18 @@ finalize_plan(PlannerInfo *root, Plan *plan, Bitmapset *valid_params,
 			context.paramids = bms_add_members(context.paramids, scan_params);
 			break;
 
+		case T_IndexOnlyScan:
+			finalize_primnode((Node *) ((IndexOnlyScan *) plan)->indexqual,
+							  &context);
+			finalize_primnode((Node *) ((IndexOnlyScan *) plan)->indexorderby,
+							  &context);
+
+			/*
+			 * we need not look at indextlist, since it cannot contain Params.
+			 */
+			context.paramids = bms_add_members(context.paramids, scan_params);
+			break;
+
 		case T_BitmapIndexScan:
 			finalize_primnode((Node *) ((BitmapIndexScan *) plan)->indexqual,
 							  &context);

src/backend/optimizer/util/pathnode.c

@@ -452,7 +452,7 @@ create_index_path(PlannerInfo *root,
 		indexscandir = NoMovementScanDirection;
 	}
 
-	pathnode->path.pathtype = T_IndexScan;
+	pathnode->path.pathtype = indexonly ? T_IndexOnlyScan : T_IndexScan;
 	pathnode->path.parent = rel;
 	pathnode->path.pathkeys = pathkeys;
 
@@ -470,7 +470,6 @@ create_index_path(PlannerInfo *root,
 
 	pathnode->isjoininner = (outer_rel != NULL);
 	pathnode->indexscandir = indexscandir;
-	pathnode->indexonly = indexonly;
 
 	if (outer_rel != NULL)
 	{

src/backend/optimizer/util/plancat.c

@@ -22,6 +22,7 @@
 #include "access/sysattr.h"
 #include "access/transam.h"
 #include "catalog/catalog.h"
+#include "catalog/heap.h"
 #include "miscadmin.h"
 #include "nodes/makefuncs.h"
 #include "optimizer/clauses.h"
@@ -49,6 +50,8 @@ static int32 get_rel_data_width(Relation rel, int32 *attr_widths);
 static List *get_relation_constraints(PlannerInfo *root,
 						 Oid relationObjectId, RelOptInfo *rel,
 						 bool include_notnull);
+static List *build_index_tlist(PlannerInfo *root, IndexOptInfo *index,
+				  Relation heapRelation);
 
 
 /*
@@ -314,6 +317,10 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
 				ChangeVarNodes((Node *) info->indexprs, 1, varno, 0);
 			if (info->indpred && varno != 1)
 				ChangeVarNodes((Node *) info->indpred, 1, varno, 0);
+
+			/* Build targetlist using the completed indexprs data */
+			info->indextlist = build_index_tlist(root, info, relation);
+
 			info->predOK = false;		/* set later in indxpath.c */
 			info->unique = index->indisunique;
 			info->hypothetical = false;
@@ -900,6 +907,70 @@ build_physical_tlist(PlannerInfo *root, RelOptInfo *rel)
 	return tlist;
 }
 
+/*
+ * build_index_tlist
+ *
+ * Build a targetlist representing the columns of the specified index.
+ * Each column is represented by a Var for the corresponding base-relation
+ * column, or an expression in base-relation Vars, as appropriate.
+ *
+ * There are never any dropped columns in indexes, so unlike
+ * build_physical_tlist, we need no failure case.
+ */
+static List *
+build_index_tlist(PlannerInfo *root, IndexOptInfo *index,
+				  Relation heapRelation)
+{
+	List	   *tlist = NIL;
+	Index		varno = index->rel->relid;
+	ListCell   *indexpr_item;
+	int			i;
+
+	indexpr_item = list_head(index->indexprs);
+	for (i = 0; i < index->ncolumns; i++)
+	{
+		int			indexkey = index->indexkeys[i];
+		Expr	   *indexvar;
+
+		if (indexkey != 0)
+		{
+			/* simple column */
+			Form_pg_attribute att_tup;
+
+			if (indexkey < 0)
+				att_tup = SystemAttributeDefinition(indexkey,
+											heapRelation->rd_rel->relhasoids);
+			else
+				att_tup = heapRelation->rd_att->attrs[indexkey - 1];
+
+			indexvar = (Expr *) makeVar(varno,
+										indexkey,
+										att_tup->atttypid,
+										att_tup->atttypmod,
+										att_tup->attcollation,
+										0);
+		}
+		else
+		{
+			/* expression column */
+			if (indexpr_item == NULL)
+				elog(ERROR, "wrong number of index expressions");
+			indexvar = (Expr *) lfirst(indexpr_item);
+			indexpr_item = lnext(indexpr_item);
+		}
+
+		tlist = lappend(tlist,
+						makeTargetEntry(indexvar,
+										i + 1,
+										NULL,
+										false));
+	}
+	if (indexpr_item != NULL)
+		elog(ERROR, "wrong number of index expressions");
+
+	return tlist;
+}
+
 /*
  * restriction_selectivity
  *

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);

src/include/executor/nodeIndexonlyscan.h

+/*-------------------------------------------------------------------------
+ *
+ * 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 */

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);

src/include/nodes/execnodes.h

@@ -1226,7 +1226,6 @@ typedef struct
  *		RuntimeContext	   expr context for evaling runtime Skeys
  *		RelationDesc	   index relation descriptor
  *		ScanDesc		   index scan descriptor
- *		VMBuffer		   buffer in use for visibility map testing, if any
  * ----------------
  */
 typedef struct IndexScanState
@@ -1243,9 +1242,42 @@ typedef struct IndexScanState
 	ExprContext *iss_RuntimeContext;
 	Relation	iss_RelationDesc;
 	IndexScanDesc iss_ScanDesc;
-	Buffer		iss_VMBuffer;
 } IndexScanState;
 
+/* ----------------
+ *	 IndexOnlyScanState information
+ *
+ *		indexqual		   execution state for indexqual expressions
+ *		ScanKeys		   Skey structures for index quals
+ *		NumScanKeys		   number of ScanKeys
+ *		OrderByKeys		   Skey structures for index ordering operators
+ *		NumOrderByKeys	   number of OrderByKeys
+ *		RuntimeKeys		   info about Skeys that must be evaluated at runtime
+ *		NumRuntimeKeys	   number of RuntimeKeys
+ *		RuntimeKeysReady   true if runtime Skeys have been computed
+ *		RuntimeContext	   expr context for evaling runtime Skeys
+ *		RelationDesc	   index relation descriptor
+ *		ScanDesc		   index scan descriptor
+ *		VMBuffer		   buffer in use for visibility map testing, if any
+ * ----------------
+ */
+typedef struct IndexOnlyScanState
+{
+	ScanState	ss;				/* its first field is NodeTag */
+	List	   *indexqual;
+	ScanKey		ioss_ScanKeys;
+	int			ioss_NumScanKeys;
+	ScanKey		ioss_OrderByKeys;
+	int			ioss_NumOrderByKeys;
+	IndexRuntimeKeyInfo *ioss_RuntimeKeys;
+	int			ioss_NumRuntimeKeys;
+	bool		ioss_RuntimeKeysReady;
+	ExprContext *ioss_RuntimeContext;
+	Relation	ioss_RelationDesc;
+	IndexScanDesc ioss_ScanDesc;
+	Buffer		ioss_VMBuffer;
+} IndexOnlyScanState;
+
 /* ----------------
  *	 BitmapIndexScanState information
  *

src/include/nodes/nodes.h

@@ -52,6 +52,7 @@ typedef enum NodeTag
 	T_Scan,
 	T_SeqScan,
 	T_IndexScan,
+	T_IndexOnlyScan,
 	T_BitmapIndexScan,
 	T_BitmapHeapScan,
 	T_TidScan,
@@ -97,6 +98,7 @@ typedef enum NodeTag
 	T_ScanState,
 	T_SeqScanState,
 	T_IndexScanState,
+	T_IndexOnlyScanState,
 	T_BitmapIndexScanState,
 	T_BitmapHeapScanState,
 	T_TidScanState,

src/include/nodes/plannodes.h

@@ -285,11 +285,8 @@ typedef Scan SeqScan;
  *
  * indexqual has the same form, but the expressions have been commuted if
  * necessary to put the indexkeys on the left, and the indexkeys are replaced
- * by Var nodes identifying the index columns (varattno is the index column
- * position, not the base table's column, even though varno is for the base
- * table).	This is a bit hokey ... would be cleaner to use a special-purpose
- * node type that could not be mistaken for a regular Var.	But it will do
- * for now.
+ * by Var nodes identifying the index columns (their varno is INDEX_VAR and
+ * their varattno is the index column number).
  *
  * indexorderbyorig is similarly the original form of any ORDER BY expressions
  * that are being implemented by the index, while indexorderby is modified to
@@ -302,8 +299,7 @@ typedef Scan SeqScan;
  * (Note these fields are used for amcanorderbyop cases, not amcanorder cases.)
  *
  * indexorderdir specifies the scan ordering, for indexscans on amcanorder
- * indexes (for other indexes it should be "don't care").  indexonly specifies
- * an index-only scan, for indexscans on amcanreturn indexes.
+ * indexes (for other indexes it should be "don't care").
  * ----------------
  */
 typedef struct IndexScan
@@ -315,9 +311,35 @@ typedef struct IndexScan
 	List	   *indexorderby;	/* list of index ORDER BY exprs */
 	List	   *indexorderbyorig;		/* the same in original form */
 	ScanDirection indexorderdir;	/* forward or backward or don't care */
-	bool		indexonly;		/* attempt to skip heap fetches? */
 } IndexScan;
 
+/* ----------------
+ *		index-only scan node
+ *
+ * IndexOnlyScan is very similar to IndexScan, but it specifies an
+ * index-only scan, in which the data comes from the index not the heap.
+ * Because of this, *all* Vars in the plan node's targetlist, qual, and
+ * index expressions reference index columns and have varno = INDEX_VAR.
+ * Hence we do not need separate indexqualorig and indexorderbyorig lists,
+ * since their contents would be equivalent to indexqual and indexorderby.
+ *
+ * To help EXPLAIN interpret the index Vars for display, we provide
+ * indextlist, which represents the contents of the index as a targetlist
+ * with one TLE per index column.  Vars appearing in this list reference
+ * the base table, and this is the only field in the plan node that may
+ * contain such Vars.
+ * ----------------
+ */
+typedef struct IndexOnlyScan
+{
+	Scan		scan;
+	Oid			indexid;		/* OID of index to scan */
+	List	   *indexqual;		/* list of index quals (usually OpExprs) */
+	List	   *indexorderby;	/* list of index ORDER BY exprs */
+	List	   *indextlist;		/* TargetEntry list describing index's cols */
+	ScanDirection indexorderdir;	/* forward or backward or don't care */
+} IndexOnlyScan;
+
 /* ----------------
  *		bitmap index scan node
  *

src/include/nodes/primnodes.h

@@ -118,15 +118,19 @@ typedef struct Expr
  * Note: during parsing/planning, varnoold/varoattno are always just copies
  * of varno/varattno.  At the tail end of planning, Var nodes appearing in
  * upper-level plan nodes are reassigned to point to the outputs of their
- * subplans; for example, in a join node varno becomes INNER or OUTER and
- * varattno becomes the index of the proper element of that subplan's target
- * list.  But varnoold/varoattno continue to hold the original values.
+ * subplans; for example, in a join node varno becomes INNER_VAR or OUTER_VAR
+ * and varattno becomes the index of the proper element of that subplan's
+ * target list.  But varnoold/varoattno continue to hold the original values.
  * The code doesn't really need varnoold/varoattno, but they are very useful
  * for debugging and interpreting completed plans, so we keep them around.
  */
-#define    INNER		65000
-#define    OUTER		65001
+#define    INNER_VAR		65000			/* reference to inner subplan */
+#define    OUTER_VAR		65001			/* reference to outer subplan */
+#define    INDEX_VAR		65002			/* reference to index column */
 
+#define IS_SPECIAL_VARNO(varno)		((varno) >= INNER_VAR)
+
+/* Symbols for the indexes of the special RTE entries in rules */
 #define    PRS2_OLD_VARNO			1
 #define    PRS2_NEW_VARNO			2
 
@@ -134,7 +138,7 @@ typedef struct Var
 {
 	Expr		xpr;
 	Index		varno;			/* index of this var's relation in the range
-								 * table (could also be INNER or OUTER) */
+								 * table, or INNER_VAR/OUTER_VAR/INDEX_VAR */
 	AttrNumber	varattno;		/* attribute number of this var, or zero for
 								 * all */
 	Oid			vartype;		/* pg_type OID for the type of this var */

src/include/nodes/relation.h

@@ -449,6 +449,10 @@ typedef struct RelOptInfo
  *		The indexprs and indpred expressions have been run through
  *		prepqual.c and eval_const_expressions() for ease of matching to
  *		WHERE clauses. indpred is in implicit-AND form.
+ *
+ *		indextlist is a TargetEntry list representing the index columns.
+ *		It provides an equivalent base-relation Var for each simple column,
+ *		and links to the matching indexprs element for each expression column.
  */
 typedef struct IndexOptInfo
 {
@@ -478,6 +482,8 @@ typedef struct IndexOptInfo
 	List	   *indexprs;		/* expressions for non-simple index columns */
 	List	   *indpred;		/* predicate if a partial index, else NIL */
 
+	List	   *indextlist;		/* targetlist representing index columns */
+
 	bool		predOK;			/* true if predicate matches query */
 	bool		unique;			/* true if a unique index */
 	bool		hypothetical;	/* true if index doesn't really exist */
@@ -640,6 +646,9 @@ typedef struct Path
 /*----------
  * IndexPath represents an index scan over a single index.
  *
+ * This struct is used for both regular indexscans and index-only scans;
+ * path.pathtype is T_IndexScan or T_IndexOnlyScan to show which is meant.
+ *
  * 'indexinfo' is the index to be scanned.
  *
  * 'indexclauses' is a list of index qualification clauses, with implicit
@@ -673,14 +682,10 @@ typedef struct Path
  * NoMovementScanDirection for an indexscan, but the planner wants to
  * distinguish ordered from unordered indexes for building pathkeys.)
  *
- * 'indexonly' is TRUE for an index-only scan, that is, the index's access
- * method has amcanreturn = TRUE and we only need columns available from the
- * index.
- *
  * 'indextotalcost' and 'indexselectivity' are saved in the IndexPath so that
  * we need not recompute them when considering using the same index in a
  * bitmap index/heap scan (see BitmapHeapPath).  The costs of the IndexPath
- * itself represent the costs of an IndexScan plan type.
+ * itself represent the costs of an IndexScan or IndexOnlyScan plan type.
  *
  * 'rows' is the estimated result tuple count for the indexscan.  This
  * is the same as path.parent->rows for a simple indexscan, but it is
@@ -698,7 +703,6 @@ typedef struct IndexPath
 	List	   *indexorderbys;
 	bool		isjoininner;
 	ScanDirection indexscandir;
-	bool		indexonly;
 	Cost		indextotalcost;
 	Selectivity indexselectivity;
 	double		rows;			/* estimated number of result tuples */
@@ -714,11 +718,12 @@ typedef struct IndexPath
  * The individual indexscans are represented by IndexPath nodes, and any
  * logic on top of them is represented by a tree of BitmapAndPath and
  * BitmapOrPath nodes.	Notice that we can use the same IndexPath node both
- * to represent a regular IndexScan plan, and as the child of a BitmapHeapPath
- * that represents scanning the same index using a BitmapIndexScan.  The
- * startup_cost and total_cost figures of an IndexPath always represent the
- * costs to use it as a regular IndexScan.	The costs of a BitmapIndexScan
- * can be computed using the IndexPath's indextotalcost and indexselectivity.
+ * to represent a regular (or index-only) index scan plan, and as the child
+ * of a BitmapHeapPath that represents scanning the same index using a
+ * BitmapIndexScan.  The startup_cost and total_cost figures of an IndexPath
+ * always represent the costs to use it as a regular (or index-only)
+ * IndexScan.  The costs of a BitmapIndexScan can be computed using the
+ * IndexPath's indextotalcost and indexselectivity.
  *
  * BitmapHeapPaths can be nestloop inner indexscans.  The isjoininner and
  * rows fields serve the same purpose as for plain IndexPaths.