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MDEV-30143 Segfault on select query using index for group-by and filesort

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The problem was trying to access JOIN_TAB::select which is set to NULL
when using the filesort. The correct way is accessing either
JOIN_TAB::select or JOIN_TAB::filesort->select depending on whether
the filesort is used.
This commit introduces member function JOIN_TAB::get_sql_select()
encapsulating that check so the code duplication is eliminated.

The new condition (s->table->quick_keys.is_set(best_key->key))
was added to  best_access_path() to eliminate a Valgrind error.
The cause of that error was using TRASH_ALLOC(quick_key_parts)
instead of bzero(quick_key_parts); hence, accessing
s->table->quick_key_parts[best_key->key]) without prior checking
for quick_keys.is_set() might have caused reading "dirty" memory
This commit is contained in:
Oleg Smirnov
2023-01-29 19:39:14 +07:00
parent 131ef14a6e
commit 60f0765b58
4 changed files with 54 additions and 6 deletions
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23
mysql-test/main/group_min_max_innodb.test
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@ -251,7 +251,28 @@ insert into t2 values (1,repeat("a",1000)),(2,repeat("a",1000)),(3,repeat("b",10
SELECT GROUP_CONCAT(t1.language_id SEPARATOR ',') AS `translation_resources`, `d`.`serialized_c` FROM t2 AS `d` LEFT JOIN t1 ON `d`.`voter_id` = t1.`voter_id` GROUP BY `d`.`voter_id` ORDER BY 10-d.voter_id+RAND()*0;
drop table t1,t2;
--echo #
--echo # MDEV-30143: Segfault on select query using index for group-by and filesort
--echo #
CREATE TABLE t1 (a varchar(35), b varchar(4)) ENGINE=InnoDB;
INSERT INTO t1 VALUES
('Albania','AXA'),('Australia','AUS'),('American Samoa','AMSA'),('Bahamas','BS');
CREATE TABLE t2 (a varchar(4), b varchar(50), PRIMARY KEY (b,a), KEY (a)) ENGINE=InnoDB;
INSERT INTO t2 VALUES
('BERM','African Methodist Episcopal'),('AUS','Anglican'),('BERM','Anglican'),('BS','Anglican'),('BS','Baptist'),('BS','Methodist');
let query=
SELECT t1.a
FROM (SELECT a FROM t2 GROUP BY a ORDER BY COUNT(DISTINCT b) LIMIT 1) dt
JOIN t1 ON dt.a=t1.b;
--replace_column 9 #
eval EXPLAIN $query;
eval $query;
DROP TABLES t1, t2;
set global innodb_stats_persistent= @innodb_stats_persistent_save;
set global innodb_stats_persistent_sample_pages=
@innodb_stats_persistent_sample_pages_save;