Fix index-only scan plans, take 2.

Commit 4ace45677 failed to fix the problem fully, because the
same issue of attempting to fetch a non-returnable index column
can occur when rechecking the indexqual after using a lossy index
operator.  Moreover, it broke EXPLAIN for such indexquals (which
indicates a gap in our test cases :-().

Revert the code changes of 4ace45677 in favor of adding a new field
to struct IndexOnlyScan, containing a version of the indexqual that
can be executed against the index-returned tuple without using any
non-returnable columns.  (The restrictions imposed by check_index_only
guarantee this is possible, although we may have to recompute indexed
expressions.)  Support construction of that during setrefs.c
processing by marking IndexOnlyScan.indextlist entries as resjunk
if they can't be returned, rather than removing them entirely.
(We could alternatively require setrefs.c to look up the IndexOptInfo
again, but abusing resjunk this way seems like a reasonably safe way
to avoid needing to do that.)

This solution isn't great from an API-stability standpoint: if there
are any extensions out there that build IndexOnlyScan structs directly,
they'll be broken in the next minor releases.  However, only a very
invasive extension would be likely to do such a thing.  There's no
change in the Path representation, so typical planner extensions
shouldn't have a problem.

As before, back-patch to all supported branches.

Discussion: https://postgr.es/m/3179992.1641150853@sss.pgh.pa.us
Discussion: https://postgr.es/m/17350-b5bdcf476e5badbb@postgresql.org

3 files changed, 55 insertions, 54 deletions

diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index ff2b14e8800..4b7347bc0e9 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -20,7 +20,6 @@
 #include <math.h>
 
 #include "access/sysattr.h"
-#include "catalog/pg_am.h"
 #include "catalog/pg_class.h"
 #include "foreign/fdwapi.h"
 #include "miscadmin.h"
@@ -189,10 +188,10 @@ static IndexScan *make_indexscan(List *qptlist, List *qpqual, Index scanrelid,
 								 ScanDirection indexscandir);
 static IndexOnlyScan *make_indexonlyscan(List *qptlist, List *qpqual,
 										 Index scanrelid, Oid indexid,
-										 List *indexqual, List *indexorderby,
+										 List *indexqual, List *recheckqual,
+										 List *indexorderby,
 										 List *indextlist,
 										 ScanDirection indexscandir);
-static List *make_indexonly_tlist(IndexOptInfo *indexinfo);
 static BitmapIndexScan *make_bitmap_indexscan(Index scanrelid, Oid indexid,
 											  List *indexqual,
 											  List *indexqualorig);
@@ -623,7 +622,7 @@ create_scan_plan(PlannerInfo *root, Path *best_path, int flags)
 		if (best_path->pathtype == T_IndexOnlyScan)
 		{
 			/* For index-only scan, the preferred tlist is the index's */
-			tlist = copyObject(make_indexonly_tlist(((IndexPath *) best_path)->indexinfo));
+			tlist = copyObject(((IndexPath *) best_path)->indexinfo->indextlist);
 
 			/*
 			 * Transfer sortgroupref data to the replacement tlist, if
@@ -2934,7 +2933,8 @@ create_indexscan_plan(PlannerInfo *root,
 	List	   *indexclauses = best_path->indexclauses;
 	List	   *indexorderbys = best_path->indexorderbys;
 	Index		baserelid = best_path->path.parent->relid;
-	Oid			indexoid = best_path->indexinfo->indexoid;
+	IndexOptInfo *indexinfo = best_path->indexinfo;
+	Oid			indexoid = indexinfo->indexoid;
 	List	   *qpqual;
 	List	   *stripped_indexquals;
 	List	   *fixed_indexquals;
@@ -3064,6 +3064,24 @@ create_indexscan_plan(PlannerInfo *root,
 		}
 	}
 
+	/*
+	 * For an index-only scan, we must mark indextlist entries as resjunk if
+	 * they are columns that the index AM can't return; this cues setrefs.c to
+	 * not generate references to those columns.
+	 */
+	if (indexonly)
+	{
+		int			i = 0;
+
+		foreach(l, indexinfo->indextlist)
+		{
+			TargetEntry *indextle = (TargetEntry *) lfirst(l);
+
+			indextle->resjunk = !indexinfo->canreturn[i];
+			i++;
+		}
+	}
+
 	/* Finally ready to build the plan node */
 	if (indexonly)
 		scan_plan = (Scan *) make_indexonlyscan(tlist,
@@ -3071,8 +3089,9 @@ create_indexscan_plan(PlannerInfo *root,
 												baserelid,
 												indexoid,
 												fixed_indexquals,
+												stripped_indexquals,
 												fixed_indexorderbys,
-												make_indexonly_tlist(best_path->indexinfo),
+												indexinfo->indextlist,
 												best_path->indexscandir);
 	else
 		scan_plan = (Scan *) make_indexscan(tlist,
@@ -5444,6 +5463,7 @@ make_indexonlyscan(List *qptlist,
 				   Index scanrelid,
 				   Oid indexid,
 				   List *indexqual,
+				   List *recheckqual,
 				   List *indexorderby,
 				   List *indextlist,
 				   ScanDirection indexscandir)
@@ -5458,6 +5478,7 @@ make_indexonlyscan(List *qptlist,
 	node->scan.scanrelid = scanrelid;
 	node->indexid = indexid;
 	node->indexqual = indexqual;
+	node->recheckqual = recheckqual;
 	node->indexorderby = indexorderby;
 	node->indextlist = indextlist;
 	node->indexorderdir = indexscandir;
@@ -5465,53 +5486,6 @@ make_indexonlyscan(List *qptlist,
 	return node;
 }
 
-/*
- * make_indexonly_tlist
- *
- * Construct the indextlist for an IndexOnlyScan plan node.
- * We must replace any column that can't be returned by the index AM
- * with a null Const of the appropriate datatype.  This is necessary
- * to prevent setrefs.c from trying to use the value of such a column,
- * and anyway it makes the indextlist a better representative of what
- * the indexscan will really return.  (We do this here, not where the
- * IndexOptInfo is originally constructed, because earlier planner
- * steps need to know what is in such columns.)
- */
-static List *
-make_indexonly_tlist(IndexOptInfo *indexinfo)
-{
-	List	   *result;
-	int			i;
-	ListCell   *lc;
-
-	/* We needn't work hard for the common case of btrees. */
-	if (indexinfo->relam == BTREE_AM_OID)
-		return indexinfo->indextlist;
-
-	result = NIL;
-	i = 0;
-	foreach(lc, indexinfo->indextlist)
-	{
-		TargetEntry *indextle = (TargetEntry *) lfirst(lc);
-
-		if (indexinfo->canreturn[i])
-			result = lappend(result, indextle);
-		else
-		{
-			TargetEntry *newtle = makeNode(TargetEntry);
-			Node	   *texpr = (Node *) indextle->expr;
-
-			memcpy(newtle, indextle, sizeof(TargetEntry));
-			newtle->expr = (Expr *) makeNullConst(exprType(texpr),
-												  exprTypmod(texpr),
-												  exprCollation(texpr));
-			result = lappend(result, newtle);
-		}
-		i++;
-	}
-	return result;
-}
-
 static BitmapIndexScan *
 make_bitmap_indexscan(Index scanrelid,
 					  Oid indexid,
diff --git a/src/backend/optimizer/plan/setrefs.c b/src/backend/optimizer/plan/setrefs.c
index 6ccec759bd2..9c2aba45a63 100644
--- a/src/backend/optimizer/plan/setrefs.c
+++ b/src/backend/optimizer/plan/setrefs.c
@@ -1142,8 +1142,26 @@ set_indexonlyscan_references(PlannerInfo *root,
 							 int rtoffset)
 {
 	indexed_tlist *index_itlist;
+	List	   *stripped_indextlist;
+	ListCell   *lc;
+
+	/*
+	 * Vars in the plan node's targetlist, qual, and recheckqual must only
+	 * reference columns that the index AM can actually return.  To ensure
+	 * this, remove non-returnable columns (which are marked as resjunk) from
+	 * the indexed tlist.  We can just drop them because the indexed_tlist
+	 * machinery pays attention to TLE resnos, not physical list position.
+	 */
+	stripped_indextlist = NIL;
+	foreach(lc, plan->indextlist)
+	{
+		TargetEntry *indextle = (TargetEntry *) lfirst(lc);
+
+		if (!indextle->resjunk)
+			stripped_indextlist = lappend(stripped_indextlist, indextle);
+	}
 
-	index_itlist = build_tlist_index(plan->indextlist);
+	index_itlist = build_tlist_index(stripped_indextlist);
 
 	plan->scan.scanrelid += rtoffset;
 	plan->scan.plan.targetlist = (List *)
@@ -1160,6 +1178,13 @@ set_indexonlyscan_references(PlannerInfo *root,
 					   INDEX_VAR,
 					   rtoffset,
 					   NUM_EXEC_QUAL((Plan *) plan));
+	plan->recheckqual = (List *)
+		fix_upper_expr(root,
+					   (Node *) plan->recheckqual,
+					   index_itlist,
+					   INDEX_VAR,
+					   rtoffset,
+					   NUM_EXEC_QUAL((Plan *) plan));
 	/* indexqual is already transformed to reference index columns */
 	plan->indexqual = fix_scan_list(root, plan->indexqual,
 									rtoffset, 1);
diff --git a/src/backend/optimizer/plan/subselect.c b/src/backend/optimizer/plan/subselect.c
index c9f7a09d102..aee52951833 100644
--- a/src/backend/optimizer/plan/subselect.c
+++ b/src/backend/optimizer/plan/subselect.c
@@ -2336,6 +2336,8 @@ finalize_plan(PlannerInfo *root, Plan *plan,
 		case T_IndexOnlyScan:
 			finalize_primnode((Node *) ((IndexOnlyScan *) plan)->indexqual,
 							  &context);
+			finalize_primnode((Node *) ((IndexOnlyScan *) plan)->recheckqual,
+							  &context);
 			finalize_primnode((Node *) ((IndexOnlyScan *) plan)->indexorderby,
 							  &context);