[MDEV-3746] LP:694443 - Wrong result with hash join and join_cache_level=6 Created: 2010-12-26  Updated: 2015-02-02  Resolved: 2012-10-04

Status: Closed
Project: MariaDB Server
Component/s: None
Affects Version/s: None
Fix Version/s: None

Type: Bug Priority: Critical
Reporter: Philip Stoev (Inactive) Assignee: Igor Babaev
Resolution: Fixed Votes: 0
Labels: Launchpad

Attachments: XML File LPexportBug694443.xml    

 Description   

In maria-5.3 , the following query:

SELECT STRAIGHT_JOIN t1.f2 FROM t1 JOIN t2 ON t1.f4 = t2.f5 WHERE ( t2.f1 OR t2.f2 ) AND t2.f3 IS NULL ;

returns no rows even though 1 row matches the WHERE predicate and is returned by all other plans.

explain:

id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 2
1 SIMPLE t2 ref f3 f3 5 const 1 Using where; Using join buffer (flat, BNLH join)

test case:

CREATE TABLE t1 (f2 int(11), f4 varchar(10)) ;
INSERT IGNORE INTO t1 VALUES ('19','time'),('24','juabngoyrt');

CREATE TABLE t2 (f5 varchar(10), f2 int(11), f1 int(11), f3 int(11), KEY (f3)) ;
INSERT IGNORE INTO t2 VALUES ('time','4',NULL,NULL);

SET SESSION join_cache_level=6;
SET SESSION optimizer_switch='join_cache_bka=off';
SELECT STRAIGHT_JOIN t1.f2 FROM t1 JOIN t2 ON t1.f4 = t2.f5 WHERE ( t2.f1 OR t2.f2 ) AND t2.f3 IS NULL ;
EXPLAIN SELECT STRAIGHT_JOIN t1.f2 FROM t1 JOIN t2 ON t1.f4 = t2.f5 WHERE ( t2.f1 OR t2.f2 ) AND t2.f3 IS NULL ;

SET SESSION join_cache_level=0;
SET SESSION optimizer_switch='index_condition_pushdown=off';
SELECT STRAIGHT_JOIN t1.f2 FROM t1 JOIN t2 ON t1.f4 = t2.f5 WHERE ( t2.f1 OR t2.f2 ) AND t2.f3 IS NULL ;

Even though this particular test case includes join_cache_bka=off, the problematic query plan was also observed without having to force it.

 Comments   
Comment by Philip Stoev (Inactive) [ 2010-12-26 ]

Re: Wrong result with hash join and join_cache_level=6
bzr version-info:

revision-id: igor@askmonty.org-20101226025414-1opbueutu602o8eu
date: 2010-12-25 18:54:14 -0800
build-date: 2010-12-26 12:03:40 +0200
revno: 2871
branch-nick: maria-5.3

Comment by Igor Babaev [ 2010-12-26 ]

Re: Wrong result with hash join and join_cache_level=6
The bug can be reproduced with join_cache_level=4, without STRAIGHT_JOIN and
with tables of a simpler structure:

MariaDB [test]> CREATE TABLE t1 (a int PRIMARY KEY);
Query OK, 0 rows affected (0.02 sec)

MariaDB [test]> INSERT INTO t1 VALUES
-> (7), (4), (9), (1), (3), (8), (2);
Query OK, 7 rows affected (0.01 sec)
Records: 7 Duplicates: 0 Warnings: 0

MariaDB [test]> CREATE TABLE t2 (a int, b int, INDEX idx (a));
Query OK, 0 rows affected (0.00 sec)

MariaDB [test]> INSERT INTO t2 VALUES
-> (NULL,10), (4,80), (7,70), (6,11), (7,90), (NULL,40),
-> (4,77), (4,50), (NULL,41), (7,99), (7,88), (8,12),
-> (1,21), (4,90), (7,91), (8,22), (6,92), (NULL,42),
-> (2,78), (2,51), (1,43), (5,97), (5,89);
Query OK, 23 rows affected (0.00 sec)
Records: 23 Duplicates: 0 Warnings: 0

MariaDB [test]>
MariaDB [test]> SET SESSION join_cache_level = 1;
Query OK, 0 rows affected (0.00 sec)

MariaDB [test]> EXPLAIN
-> SELECT * FROM t1,t2 WHERE t1.a < 3 and t2.a IS NULL;
-------------------------------------------------------------------------------------+

id select_type table type possible_keys key key_len ref rows Extra

-------------------------------------------------------------------------------------+

1 SIMPLE t1 range PRIMARY PRIMARY 4 NULL 3 Using where; Using index
1 SIMPLE t2 ref idx idx 5 const 4 Using index condition

-------------------------------------------------------------------------------------+
2 rows in set (0.00 sec)

MariaDB [test]> SELECT * FROM t1,t2 WHERE t1.a < 3 and t2.a IS NULL;
-----------

a a b

-----------

1 NULL 10
1 NULL 40
1 NULL 41
1 NULL 42
2 NULL 10
2 NULL 40
2 NULL 41
2 NULL 42

-----------
8 rows in set (0.00 sec)

MariaDB [test]> SET SESSION join_cache_level = 4;
Query OK, 0 rows affected (0.00 sec)

MariaDB [test]> EXPLAIN
-> SELECT * FROM t1,t2 WHERE t1.a < 3 and t2.a IS NULL;
-------------------------------------------------------------------------------------------------------------+

id select_type table type possible_keys key key_len ref rows Extra

-------------------------------------------------------------------------------------------------------------+

1 SIMPLE t1 range PRIMARY PRIMARY 4 NULL 3 Using where; Using index
1 SIMPLE t2 ref idx idx 5 const 4 Using where; Using join buffer (flat, BNLH join)

-------------------------------------------------------------------------------------------------------------+
2 rows in set (0.00 sec)

MariaDB [test]> SELECT * FROM t1,t2 WHERE t1.a < 3 and t2.a IS NULL;
Empty set (0.00 sec)

Comment by Rasmus Johansson (Inactive) [ 2011-12-13 ]

Launchpad bug id: 694443

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