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From:Rick James Date:October 9 2012 5:44pm
Subject:RE: Query Cache Crashing
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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 cache being
purged.  For that reason, we (Yahoo) almost never use the QC on any 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 than 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
> 
> Hi MySql,
> 
> 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?
> 
> Twice I have had a core-dump (show at end of mail) on two separate
> servers running this version.
> 
> Now I had a complete lock, where 'SHOW PROCESSLIST' showed this for
> every connection:
> 
> "Waiting for query cache lock"
> 
> This resulted in connections building until the limit was hit.  I could
> only cure this with a 'kill -9' on the mysqld process.
> 
> Are any other users experiencing this?  Do any users know of a fix?
> 
> Thanks!
> 
> Ben Clewett.
> 
> 
> 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 = 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]
> 
> /usr/sbin/mysqld(_ZN11Query_cache19free_query_internalEP17Query_cache_b
> lock+0x7a)[0x5bdb5a]
> 
> /usr/sbin/mysqld(_ZN11Query_cache27invalidate_query_block_listEP3THDP23
> Query_cache_block_table+0x7e)[0x5be8ee]
> 
> /usr/sbin/mysqld(_ZN11Query_cache12insert_tableEjPcP23Query_cache_block
> _tablejhPFcP3THDS0_jPyEy+0x91)[0x5bf7e1]
> 
> /usr/sbin/mysqld(_ZN11Query_cache25register_tables_from_listEP10TABLE_L
> ISTjP23Query_cache_block_table+0x176)[0x5bfa76]
> 
> /usr/sbin/mysqld(_ZN11Query_cache19register_all_tablesEP17Query_cache_b
> lockP10TABLE_LISTj+0x15)[0x5bfbb5]
> 
> /usr/sbin/mysqld(_ZN11Query_cache11store_queryEP3THDP10TABLE_LIST+0x39e
> )[0x5bff5e]
> 
> /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]
> 
> /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]
> 
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Thread
Query Cache CrashingBen Clewett9 Oct
  • RE: Query Cache CrashingRick James9 Oct
    • Re: Query Cache CrashingBen Clewett10 Oct