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, 28 insertions, 1 deletions

diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index 5100642dd63..24ac5295f60 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/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;