Debugging mysqld crashes

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Author: Michal Marek <mmarek@suse.cz>

Last modified: 2014-11-21

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Contents

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1) Query log

2) Coredumps and Backtraces

3) Trace files

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In case your MySQL server crashes, here are some hints on what to

include in a bugreport at https://bugzilla.novell.com/ . Please report

there only bugs in the MySQL packages packaged by Novell/SUSE, bugs in

binaries / source provided by MySQL AB should be reported at

http://bugs.mysql.com/ .

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1) Query log

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  Note: Skip this chapter if you already have an exact query that

  crashes the server

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To find out which query possibly crashed the server, add the following

line to your /etc/my.cnf into section [mysqld]:

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    log=/var/lib/mysql/mysqld-query.log

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Mysqld then will, at some performance cost, log all queries into this

file. After a server crash, you can examine the queries from the time it

crashed and try to reproduce the crash with single queries (this might

not allways work, eg. if the crash is caused by some race condition).

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Note that this log file may become extremly large, so if you decide to

attach it whole to the bugzilla, don't forget to

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    xz -k9 /var/lib/mysql/mysqld-query.log

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and attach the xzipped file instead.

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2) Coredumps and Backtraces

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Another valuable information for the developers is the backtrace. The

easies way to get one is to let mysqld produce a coredump. Add the

following line to your /etc/my.cnf into section [mysqld]:

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    core-file

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The core file will be written to the /var/lib/mysql/ directory. I

suggest setting the kernel variable kernel.core_uses_pid to 1

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    sysctl -w kernel.core_uses_pid=1

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so that the coredumps don't overwrite each other if you experience

multiple crashes.

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After you got the core file, install the gdb and mysql-debuginfo

packages and run

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    gdb /usr/sbin/mysqld /var/lib/mysql/<core>

    (gdb) bt

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Replace the <core> with the actual name of the coredump.

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3) Trace files

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The trace file will contain various debug information and function

calls/returns and will become _extremly_ huge after a while, so don't

attach it to bugzilla unless requested.

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Add the following line to your /etc/my.cnf into section [mysqld]:

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    stack-trace

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The trace file will be then written to /var/lib/mysql directory.

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