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MDEV-14526: MariaDB keeps crashing under load when query_cache_type is changed

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The problem was in such scenario:
T1 - starts registering query and locked QC
T2 - starts disabling QC and wait for UNLOCK
T1 - unlock QC
T2 - disable QC and destroy signals without waiting for query unlock
T1 a) - not yet unlocked query in qc and crash on attempt to unlock because
        QC signals are destroyed
   b) if above was done before destruction, it execute end_of results first
      time at exit on after try_lock which see QC disables and return TRUE.
      But it do not reset query_cache_tls->first_query_block which lead to
      second call of end_of_result when diagnostic arena has already
      inappropriate status (not is_eof()).

Fix is:
  1) wait for all queries unlocked before destroying them by locking and
     unlocking
  2) remove query_cache_tls->first_query_block if QC disabled
This commit is contained in:
Oleksandr Byelkin
2018-01-12 18:17:55 +01:00
parent b75d767689
commit 5fe1d7d076
3 changed files with 96 additions and 1 deletions
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52
mysql-test/t/query_cache_debug.test
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@ -319,3 +319,55 @@ RESET QUERY CACHE;
DROP TABLE t1;
SET GLOBAL query_cache_size= DEFAULT;
SET GLOBAL query_cache_type= DEFAULT;
--echo #
--echo # MDEV-14526: MariaDB keeps crashing under load when
--echo # query_cache_type is changed
--echo #
CREATE TABLE t1 (
`id` int(10) NOT NULL AUTO_INCREMENT,
`k` int(10) default '0',
PRIMARY KEY (`id`))
ENGINE=MyISAM;
INSERT IGNORE INTO t1 VALUES
(NULL,1),(NULL,8),(NULL,NULL),(NULL,NULL),(NULL,4),(NULL,9),(NULL,7),
(NULL,3),(NULL,NULL),(NULL,2),(NULL,3),(NULL,NULL),(NULL,2),(NULL,7),
(NULL,1),(NULL,2),(NULL,4),(NULL,NULL),(NULL,1),(NULL,1),(NULL,4);
SET GLOBAL query_cache_size= 1024*1024;
SET GLOBAL query_cache_type= 1;
--connect (con2,localhost,root,,test)
--connect (con1,localhost,root,,test)
set debug_sync="wait_in_query_cache_store_query SIGNAL parked WAIT_FOR go";
--send
SELECT DISTINCT id FROM t1 WHERE id BETWEEN 5603 AND 16218 ORDER BY k;
--connection default
set debug_sync="now WAIT_FOR parked";
--connection con2
--send
SET GLOBAL query_cache_type= 0;
--connection default
set debug_sync="now SIGNAL go";
--connection con1
--reap
--connection con2
--reap
# Cleanup
--disconnect con1
--disconnect con2
--connection default
set debug_sync= 'RESET';
DROP TABLE t1;
SEt GLOBAL query_cache_size= DEFAULT;
SEt GLOBAL query_cache_type= DEFAULT;
--echo # End of 5.5 tests