Take OUTER JOIN semantics into account when estimating the size of join

relations.  It's not very bright, but at least it now knows that
A LEFT JOIN B must produce at least as many rows as are in A ...

diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c
index cc9e49b9e221dfeaf59ad93cb2c199244de4e32d..8e88e46d571068c5f6318d7a1a8e349224701145 100644 (file)
--- a/src/backend/optimizer/path/costsize.c
+++ b/src/backend/optimizer/path/costsize.c
@@ -41,7 +41,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *       $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.67 2001/02/15 17:46:40 tgl Exp $
+ *       $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.68 2001/02/16 00:03:07 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -837,11 +837,12 @@ void
 set_joinrel_size_estimates(Query *root, RelOptInfo *rel,
                                                   RelOptInfo *outer_rel,
                                                   RelOptInfo *inner_rel,
+                                                  JoinType jointype,
                                                   List *restrictlist)
 {
        double          temp;
 
-       /* cartesian product */
+       /* Start with the Cartesian product */
        temp = outer_rel->rows * inner_rel->rows;
 
        /*
@@ -854,6 +855,35 @@ set_joinrel_size_estimates(Query *root, RelOptInfo *rel,
                                                                         restrictlist,
                                                                         0);
 
+       /*
+        * If we are doing an outer join, take that into account: the output
+        * must be at least as large as the non-nullable input.  (Is there any
+        * chance of being even smarter?)
+        */
+       switch (jointype)
+       {
+               case JOIN_INNER:
+                       break;
+               case JOIN_LEFT:
+                       if (temp < outer_rel->rows)
+                               temp = outer_rel->rows;
+                       break;
+               case JOIN_RIGHT:
+                       if (temp < inner_rel->rows)
+                               temp = inner_rel->rows;
+                       break;
+               case JOIN_FULL:
+                       if (temp < outer_rel->rows)
+                               temp = outer_rel->rows;
+                       if (temp < inner_rel->rows)
+                               temp = inner_rel->rows;
+                       break;
+               default:
+                       elog(ERROR, "set_joinrel_size_estimates: unsupported join type %d",
+                                (int) jointype);
+                       break;
+       }
+
        /*
         * Force estimate to be at least one row, to make explain output look
         * better and to avoid possible divide-by-zero when interpolating
@@ -861,6 +891,7 @@ set_joinrel_size_estimates(Query *root, RelOptInfo *rel,
         */
        if (temp < 1.0)
                temp = 1.0;
+
        rel->rows = temp;
 
        /*

diff --git a/src/backend/optimizer/path/joinrels.c b/src/backend/optimizer/path/joinrels.c
index 2a59ed43e48f360b0abb5ffb80a88f25b3c1e13a..2492f17ea9b5c2cb5a3de5a6b253e461d91fe9cb 100644 (file)
--- a/src/backend/optimizer/path/joinrels.c
+++ b/src/backend/optimizer/path/joinrels.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *       $Header: /cvsroot/pgsql/src/backend/optimizer/path/joinrels.c,v 1.50 2001/01/24 19:42:58 momjian Exp $
+ *       $Header: /cvsroot/pgsql/src/backend/optimizer/path/joinrels.c,v 1.51 2001/02/16 00:03:07 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -394,7 +394,7 @@ make_join_rel(Query *root, RelOptInfo *rel1, RelOptInfo *rel2,
         * Find or build the join RelOptInfo, and compute the restrictlist
         * that goes with this particular joining.
         */
-       joinrel = get_join_rel(root, rel1, rel2, &restrictlist);
+       joinrel = get_join_rel(root, rel1, rel2, jointype, &restrictlist);
 
        /*
         * Consider paths using each rel as both outer and inner.

diff --git a/src/backend/optimizer/util/relnode.c b/src/backend/optimizer/util/relnode.c
index 57827c813f38d43c2d76135b00b618635314591f..b4764ab6f8cd08295a6913ccf680c9d7c5cb9a47 100644 (file)
--- a/src/backend/optimizer/util/relnode.c
+++ b/src/backend/optimizer/util/relnode.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *       $Header: /cvsroot/pgsql/src/backend/optimizer/util/relnode.c,v 1.31 2001/01/24 19:43:00 momjian Exp $
+ *       $Header: /cvsroot/pgsql/src/backend/optimizer/util/relnode.c,v 1.32 2001/02/16 00:03:08 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -152,6 +152,7 @@ find_join_rel(Query *root, Relids relids)
  *
  * 'outer_rel' and 'inner_rel' are relation nodes for the relations to be
  *             joined
+ * 'jointype': type of join (inner/outer)
  * 'restrictlist_ptr': result variable.  If not NULL, *restrictlist_ptr
  *             receives the list of RestrictInfo nodes that apply to this
  *             particular pair of joinable relations.
@@ -163,6 +164,7 @@ RelOptInfo *
 get_join_rel(Query *root,
                         RelOptInfo *outer_rel,
                         RelOptInfo *inner_rel,
+                        JoinType jointype,
                         List **restrictlist_ptr)
 {
        List       *joinrelids;
@@ -252,7 +254,7 @@ get_join_rel(Query *root,
         * Set estimates of the joinrel's size.
         */
        set_joinrel_size_estimates(root, joinrel, outer_rel, inner_rel,
-                                                          restrictlist);
+                                                          jointype, restrictlist);
 
        /*
         * Add the joinrel to the query's joinrel list.

diff --git a/src/include/optimizer/cost.h b/src/include/optimizer/cost.h
index c6dfcac39c983028f6392f4c2eb4630310ff5b3c..5caa576f0c0be002c3e1bc88a7ff75746f5c45b4 100644 (file)
--- a/src/include/optimizer/cost.h
+++ b/src/include/optimizer/cost.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: cost.h,v 1.37 2001/01/24 19:43:26 momjian Exp $
+ * $Id: cost.h,v 1.38 2001/02/16 00:03:05 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -70,6 +70,7 @@ extern void set_baserel_size_estimates(Query *root, RelOptInfo *rel);
 extern void set_joinrel_size_estimates(Query *root, RelOptInfo *rel,
                                                   RelOptInfo *outer_rel,
                                                   RelOptInfo *inner_rel,
+                                                  JoinType jointype,
                                                   List *restrictlist);
 
 /*

diff --git a/src/include/optimizer/pathnode.h b/src/include/optimizer/pathnode.h
index b4e239aa8f712e79ca7786735dbba385fa9a91f9..7e000034761e03e467c4875aa535ddcbd929a05d 100644 (file)
--- a/src/include/optimizer/pathnode.h
+++ b/src/include/optimizer/pathnode.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: pathnode.h,v 1.33 2001/01/24 19:43:26 momjian Exp $
+ * $Id: pathnode.h,v 1.34 2001/02/16 00:03:06 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -66,8 +66,10 @@ extern HashPath *create_hashjoin_path(RelOptInfo *joinrel,
  */
 extern RelOptInfo *get_base_rel(Query *root, int relid);
 extern RelOptInfo *make_base_rel(Query *root, int relid);
-extern RelOptInfo *get_join_rel(Query *root, RelOptInfo *outer_rel,
-                        RelOptInfo *inner_rel,
-                        List **restrictlist_ptr);
+extern RelOptInfo *get_join_rel(Query *root,
+                                                               RelOptInfo *outer_rel,
+                                                               RelOptInfo *inner_rel,
+                                                               JoinType jointype,
+                                                               List **restrictlist_ptr);
 
 #endif  /* PATHNODE_H */