From d5a4b69c3a0d2668fa6098c73be7b6f0036bb642 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sat, 12 Sep 2009 00:04:59 +0000
Subject: [PATCH] Fix assertion failure when a SELECT DISTINCT ON expression is
volatile. In this case we generate two PathKey references to the expression
(one for DISTINCT and one for ORDER BY) and they really need to refer to the
same EquivalenceClass. However get_eclass_for_sort_expr was being overly
paranoid and creating two different EC's. Correct behavior is to use the
SortGroupRef index to decide whether two references to volatile expressions
that are equal() (ie textually equivalent) should be considered the same.
Backpatch to 8.4. Possibly this should be changed in 8.3 as well, but
I'll refrain in the absence of evidence of a visible failure in that branch.
Per bug #5049.
---
src/backend/optimizer/path/equivclass.c | 16 ++++++++++++----
src/backend/optimizer/path/pathkeys.c | 11 ++++++++++-
src/test/regress/expected/select_distinct_on.out | 7 +++++++
src/test/regress/sql/select_distinct_on.sql | 3 +++
4 files changed, 32 insertions(+), 5 deletions(-)
diff --git a/src/backend/optimizer/path/equivclass.c b/src/backend/optimizer/path/equivclass.c
index 17d24e400f8..ff3af5ee102 100644
--- a/src/backend/optimizer/path/equivclass.c
+++ b/src/backend/optimizer/path/equivclass.c
@@ -10,7 +10,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/optimizer/path/equivclass.c,v 1.19 2009/06/11 14:48:58 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/optimizer/path/equivclass.c,v 1.20 2009/09/12 00:04:58 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -357,7 +357,7 @@ add_eq_member(EquivalenceClass *ec, Expr *expr, Relids relids,
* EquivalenceClass for it.
*
* sortref is the SortGroupRef of the originating SortGroupClause, if any,
- * or zero if not.
+ * or zero if not. (It should never be zero if the expression is volatile!)
*
* This can be used safely both before and after EquivalenceClass merging;
* since it never causes merging it does not invalidate any existing ECs
@@ -388,8 +388,12 @@ get_eclass_for_sort_expr(PlannerInfo *root,
EquivalenceClass *cur_ec = (EquivalenceClass *) lfirst(lc1);
ListCell *lc2;
- /* Never match to a volatile EC */
- if (cur_ec->ec_has_volatile)
+ /*
+ * Never match to a volatile EC, except when we are looking at another
+ * reference to the same volatile SortGroupClause.
+ */
+ if (cur_ec->ec_has_volatile &&
+ (sortref == 0 || sortref != cur_ec->ec_sortref))
continue;
if (!equal(opfamilies, cur_ec->ec_opfamilies))
@@ -433,6 +437,10 @@ get_eclass_for_sort_expr(PlannerInfo *root,
newec->ec_broken = false;
newec->ec_sortref = sortref;
newec->ec_merged = NULL;
+
+ if (newec->ec_has_volatile && sortref == 0) /* should not happen */
+ elog(ERROR, "volatile EquivalenceClass has no sortref");
+
newem = add_eq_member(newec, expr, pull_varnos((Node *) expr),
false, expr_datatype);
diff --git a/src/backend/optimizer/path/pathkeys.c b/src/backend/optimizer/path/pathkeys.c
index 2693cc154d5..aae3fc95045 100644
--- a/src/backend/optimizer/path/pathkeys.c
+++ b/src/backend/optimizer/path/pathkeys.c
@@ -11,7 +11,7 @@
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/optimizer/path/pathkeys.c,v 1.98 2009/07/17 23:19:34 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/optimizer/path/pathkeys.c,v 1.99 2009/09/12 00:04:59 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -635,6 +635,15 @@ convert_subquery_pathkeys(PlannerInfo *root, RelOptInfo *rel,
exprType((Node *) tle->expr),
exprTypmod((Node *) tle->expr),
0);
+
+ /*
+ * Note: it might look funny to be setting sortref = 0 for
+ * a reference to a volatile sub_eclass. However, the
+ * expression is *not* volatile in the outer query: it's
+ * just a Var referencing whatever the subquery emitted.
+ * (IOW, the outer query isn't going to re-execute the
+ * volatile expression itself.) So this is okay.
+ */
outer_ec =
get_eclass_for_sort_expr(root,
outer_expr,
diff --git a/src/test/regress/expected/select_distinct_on.out b/src/test/regress/expected/select_distinct_on.out
index fc6dda7477f..b787b307f69 100644
--- a/src/test/regress/expected/select_distinct_on.out
+++ b/src/test/regress/expected/select_distinct_on.out
@@ -66,3 +66,10 @@ SELECT DISTINCT ON (string4, ten) string4, ten, two
VVVVxx | 0 | 0
(40 rows)
+-- bug #5049: early 8.4.x chokes on volatile DISTINCT ON clauses
+select distinct on (1) floor(random()) as r, f1 from int4_tbl order by 1,2;
+ r | f1
+---+-------------
+ 0 | -2147483647
+(1 row)
+
diff --git a/src/test/regress/sql/select_distinct_on.sql b/src/test/regress/sql/select_distinct_on.sql
index 54d98ca6979..d18733d274c 100644
--- a/src/test/regress/sql/select_distinct_on.sql
+++ b/src/test/regress/sql/select_distinct_on.sql
@@ -14,3 +14,6 @@ SELECT DISTINCT ON (string4, ten) string4, two, ten
SELECT DISTINCT ON (string4, ten) string4, ten, two
FROM tmp
ORDER BY string4 using <, ten using >, two using <;
+
+-- bug #5049: early 8.4.x chokes on volatile DISTINCT ON clauses
+select distinct on (1) floor(random()) as r, f1 from int4_tbl order by 1,2;
--
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