From: Rick James
Date: October 9 2012 5:44pm
Subject: RE: Query Cache Crashing
List-Archive: http://lists.mysql.com/mysql/228354
Message-Id: <2E7DD7ADE53B044C8C8BCD9C5829E1EB148CF92620@SP2-EX07VS01.ds.corp.yahoo.com>
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As for the crash, I don't know.  Instead, I recommend either shrinking the =
size (if you use a big QC) or turning it off.  This would make the issue go=
 away.

ANY modification to a particular table leads to ALL entries in the Query ca=
che being purged.  For that reason, we (Yahoo) almost never use the QC on a=
ny of our many servers.

Please provide
SHOW GLOBAL VARIABLES LIKE 'query%';
SHOW GLOBAL STATUS LIKE 'Qc%';

Because of inefficiencies in 'pruning', having a query_cache_size bigger th=
an 50M may actually degrade performance.

In you have a reproducible test case, submit to bugs.mysql.com .


> -----Original Message-----
> From: Ben Clewett [mailto:ben@stripped]
> Sent: Tuesday, October 09, 2012 4:47 AM
> To: mysql@stripped
> Subject: Query Cache Crashing
>=20
> Hi MySql,
>=20
> Since upgrading to 5.5.27 (5.5.27-ndb-7.2.8-cluster-gpl-log to be
> exact) I have experienced problems with the query cache.  I am
> wondering if I am the only one?
>=20
> Twice I have had a core-dump (show at end of mail) on two separate
> servers running this version.
>=20
> Now I had a complete lock, where 'SHOW PROCESSLIST' showed this for
> every connection:
>=20
> "Waiting for query cache lock"
>=20
> This resulted in connections building until the limit was hit.  I could
> only cure this with a 'kill -9' on the mysqld process.
>=20
> Are any other users experiencing this?  Do any users know of a fix?
>=20
> Thanks!
>=20
> Ben Clewett.
>=20
>=20
> Thread pointer: 0x7f6ea014cf90
> Attempting backtrace. You can use the following information to find out
> where mysqld died. If you see no messages after this, something went
> terribly wrong...
> stack_bottom =3D 410220e8 thread_stack 0x40000
> /usr/sbin/mysqld(my_print_stacktrace+0x35)[0x81c7f5]
> /usr/sbin/mysqld(handle_fatal_signal+0x403)[0x6e9383]
> /lib64/libpthread.so.0[0x7f6f491b2b30]
> /usr/sbin/mysqld(_ZN11Query_cache12unlink_tableEP23Query_cache_block_ta
> ble+0x1b)[0x5bd1ab]
>=20
> /usr/sbin/mysqld(_ZN11Query_cache19free_query_internalEP17Query_cache_b
> lock+0x7a)[0x5bdb5a]
>=20
> /usr/sbin/mysqld(_ZN11Query_cache27invalidate_query_block_listEP3THDP23
> Query_cache_block_table+0x7e)[0x5be8ee]
>=20
> /usr/sbin/mysqld(_ZN11Query_cache12insert_tableEjPcP23Query_cache_block
> _tablejhPFcP3THDS0_jPyEy+0x91)[0x5bf7e1]
>=20
> /usr/sbin/mysqld(_ZN11Query_cache25register_tables_from_listEP10TABLE_L
> ISTjP23Query_cache_block_table+0x176)[0x5bfa76]
>=20
> /usr/sbin/mysqld(_ZN11Query_cache19register_all_tablesEP17Query_cache_b
> lockP10TABLE_LISTj+0x15)[0x5bfbb5]
>=20
> /usr/sbin/mysqld(_ZN11Query_cache11store_queryEP3THDP10TABLE_LIST+0x39e
> )[0x5bff5e]
>=20
> /usr/sbin/mysqld[0x5eb02d]
> /usr/sbin/mysqld(_Z21mysql_execute_commandP3THD+0x269b)[0x5f0aeb]
> /usr/sbin/mysqld(_Z11mysql_parseP3THDPcjP12Parser_state+0x18a)[0x5f2cba
> ]
> /usr/sbin/mysqld(_Z16dispatch_command19enum_server_commandP3THDPcj+0x13
> 21)[0x5f4861]
>=20
> /usr/sbin/mysqld(_Z24do_handle_one_connectionP3THD+0x167)[0x68d807]
> /usr/sbin/mysqld(handle_one_connection+0x54)[0x68d874]
> /lib64/libpthread.so.0[0x7f6f491ab040]
> /lib64/libc.so.6(clone+0x6d)[0x7f6f4847c08d]
>=20
> --
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