Fix coredump seen when doing mergejoin between indexed tables,

for example in the regression test database, try
select * from tenk1 t1, tenk1 t2 where t1.unique1 = t2.unique2;
6.5 has this same bug ...

diff --git a/src/backend/optimizer/util/pathnode.c b/src/backend/optimizer/util/pathnode.c
index aa0aedb453055209ddd9a8db4749af00bff1fd7e..de5f2fda5b2d04e20064593299bf543aad072ee6 100644 (file)
--- a/src/backend/optimizer/util/pathnode.c
+++ b/src/backend/optimizer/util/pathnode.c
@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *       $Header: /cvsroot/pgsql/src/backend/optimizer/util/pathnode.c,v 1.49 1999/07/27 03:51:05 tgl Exp $
+ *       $Header: /cvsroot/pgsql/src/backend/optimizer/util/pathnode.c,v 1.50 1999/07/30 00:56:17 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -329,11 +329,16 @@ create_index_path(Query *root,
 
        /* Note that we are making a pathnode for a single-scan indexscan;
         * therefore, both indexid and indexqual should be single-element
-        * lists (unless indexqual is empty).
+        * lists.  We initialize indexqual to contain one empty sublist,
+        * representing a single index traversal with no index restriction
+        * conditions.  If we do have restriction conditions to use, they
+        * will get inserted below.
         */
+       Assert(length(index->relids) == 1);
        pathnode->indexid = index->relids;
+       pathnode->indexqual = lcons(NIL, NIL);
+
        pathnode->indexkeys = index->indexkeys;
-       pathnode->indexqual = NIL;
 
        /*
         * The index must have an ordering for the path to have (ordering)
@@ -358,14 +363,19 @@ create_index_path(Query *root,
 
        if (is_join_scan || restriction_clauses == NULL)
        {
-
                /*
                 * Indices used for joins or sorting result nodes don't restrict
                 * the result at all, they simply order it, so compute the scan
                 * cost accordingly -- use a selectivity of 1.0.
+                *
+                * is the statement above really true?  what about IndexScan as the
+                * inner of a join?
+                *
+                * I think it's OK --- this routine is only used to make index paths
+                * for mergejoins and sorts.  Index paths used as the inner side of
+                * a nestloop join do provide restriction, but they are not made
+                * with this code.  See index_innerjoin() in indxpath.c.
                 */
-/* is the statement above really true? what about IndexScan as the
-   inner of a join? */
                pathnode->path.path_cost = cost_index(lfirsti(index->relids),
                                                                                          index->pages,
                                                                                          1.0,
@@ -378,8 +388,8 @@ create_index_path(Query *root,
        else
        {
                /*
-                * Compute scan cost for the case when 'index' is used with a
-                * restriction clause.
+                * Compute scan cost for the case when 'index' is used with
+                * restriction clause(s).
                 */
                List       *indexquals;
                float           npages;
@@ -390,6 +400,11 @@ create_index_path(Query *root,
                /* expand special operators to indexquals the executor can handle */
                indexquals = expand_indexqual_conditions(indexquals);
 
+               /* Insert qual list into 1st sublist of pathnode->indexqual;
+                * we already made the cons cell above, no point in wasting it...
+                */
+               lfirst(pathnode->indexqual) = indexquals;
+
                index_selectivity(root,
                                                  lfirsti(rel->relids),
                                                  lfirsti(index->relids),
@@ -397,7 +412,6 @@ create_index_path(Query *root,
                                                  &npages,
                                                  &selec);
 
-               pathnode->indexqual = lcons(indexquals, NIL);
                pathnode->path.path_cost = cost_index(lfirsti(index->relids),
                                                                                          (int) npages,
                                                                                          selec,