Fix index-only scan plans when not all index columns can be returned.

If an index has both returnable and non-returnable columns, and one of
the non-returnable columns is an expression using a Var that is in a
returnable column, then a query returning that expression could result
in an index-only scan plan that attempts to read the non-returnable
column, instead of recomputing the expression from the returnable
column as intended.

To fix, redefine the "indextlist" list of an IndexOnlyScan plan node
as containing null Consts in place of any non-returnable columns.
This solves the problem by preventing setrefs.c from falsely matching
to such entries.  The executor is happy since it only cares about the
exposed types of the entries, and ruleutils.c doesn't care because a
correct plan won't reference those entries.  I considered some other
ways to prevent setrefs.c from doing the wrong thing, but this way
seems good since (a) it allows a very localized fix, (b) it makes
the indextlist structure more compact in many cases, and (c) the
indextlist is now a more faithful representation of what the index AM
will actually produce, viz. nulls for any non-returnable columns.

This is easier to hit since we introduced included columns, but it's
possible to construct failing examples without that, as per the
added regression test.  Hence, back-patch to all supported branches.

Per bug #17350 from Louis Jachiet.

Discussion: https://postgr.es/m/17350-b5bdcf476e5badbb@postgresql.org

diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index f12660a2606fdbe97cdcf33f5479b75798489743..ff2b14e880065fb428dff6c8ddcc8d2600cdfac6 100644 (file)
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -20,6 +20,7 @@
 #include <math.h>
 
 #include "access/sysattr.h"
+#include "catalog/pg_am.h"
 #include "catalog/pg_class.h"
 #include "foreign/fdwapi.h"
 #include "miscadmin.h"
@@ -191,6 +192,7 @@ static IndexOnlyScan *make_indexonlyscan(List *qptlist, List *qpqual,
                                                                                 List *indexqual, 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);
@@ -621,7 +623,7 @@ 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(((IndexPath *) best_path)->indexinfo->indextlist);
+                       tlist = copyObject(make_indexonly_tlist(((IndexPath *) best_path)->indexinfo));
 
                        /*
                         * Transfer sortgroupref data to the replacement tlist, if
@@ -3070,7 +3072,7 @@ create_indexscan_plan(PlannerInfo *root,
                                                                                                indexoid,
                                                                                                fixed_indexquals,
                                                                                                fixed_indexorderbys,
-                                                                                               best_path->indexinfo->indextlist,
+                                                                                               make_indexonly_tlist(best_path->indexinfo),
                                                                                                best_path->indexscandir);
        else
                scan_plan = (Scan *) make_indexscan(tlist,
@@ -5463,6 +5465,53 @@ 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/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
index be3c30704ad19a3f74fa73027aff8ac7504dd284..13e07ead31a6f13ffd0abb13007968c02bc4661d 100644 (file)
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -427,7 +427,8 @@ typedef struct IndexScan
  * 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.
+ * contain such Vars.  Note however that index columns that the AM can't
+ * reconstruct are replaced by null Consts in indextlist.
  * ----------------
  */
 typedef struct IndexOnlyScan

diff --git a/src/test/regress/expected/gist.out b/src/test/regress/expected/gist.out
index 90edb4061d4d16ab9b42fb9462ca7001061a2d70..6c6ced91e9c3899ca963f23b80617d7066ac101c 100644 (file)
--- a/src/test/regress/expected/gist.out
+++ b/src/test/regress/expected/gist.out
@@ -312,6 +312,34 @@ and p <@ box(point(5,5), point(6, 6));
 (11 rows)
 
 drop index gist_tbl_multi_index;
+-- Test that we don't try to return the value of a non-returnable
+-- column in an index-only scan.  (This isn't GIST-specific, but
+-- it only applies to index AMs that can return some columns and not
+-- others, so GIST with appropriate opclasses is a convenient test case.)
+create index gist_tbl_multi_index on gist_tbl using gist (circle(p,1), p);
+explain (verbose, costs off)
+select circle(p,1) from gist_tbl
+where p <@ box(point(5, 5), point(5.3, 5.3));
+                          QUERY PLAN                           
+---------------------------------------------------------------
+ Index Only Scan using gist_tbl_multi_index on public.gist_tbl
+   Output: circle(p, '1'::double precision)
+   Index Cond: (gist_tbl.p <@ '(5.3,5.3),(5,5)'::box)
+(3 rows)
+
+select circle(p,1) from gist_tbl
+where p <@ box(point(5, 5), point(5.3, 5.3));
+     circle      
+-----------------
+ <(5,5),1>
+ <(5.05,5.05),1>
+ <(5.1,5.1),1>
+ <(5.15,5.15),1>
+ <(5.2,5.2),1>
+ <(5.25,5.25),1>
+ <(5.3,5.3),1>
+(7 rows)
+
 -- Clean up
 reset enable_seqscan;
 reset enable_bitmapscan;

diff --git a/src/test/regress/sql/gist.sql b/src/test/regress/sql/gist.sql
index b9d398ea9417aad24c9f074fb093c1fe9322ba49..c6bac320b162bd2ff094c63a1ca673349b80b4ab 100644 (file)
--- a/src/test/regress/sql/gist.sql
+++ b/src/test/regress/sql/gist.sql
@@ -142,6 +142,17 @@ and p <@ box(point(5,5), point(6, 6));
 
 drop index gist_tbl_multi_index;
 
+-- Test that we don't try to return the value of a non-returnable
+-- column in an index-only scan.  (This isn't GIST-specific, but
+-- it only applies to index AMs that can return some columns and not
+-- others, so GIST with appropriate opclasses is a convenient test case.)
+create index gist_tbl_multi_index on gist_tbl using gist (circle(p,1), p);
+explain (verbose, costs off)
+select circle(p,1) from gist_tbl
+where p <@ box(point(5, 5), point(5.3, 5.3));
+select circle(p,1) from gist_tbl
+where p <@ box(point(5, 5), point(5.3, 5.3));
+
 -- Clean up
 reset enable_seqscan;
 reset enable_bitmapscan;