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mk-slave-restart

NAME

mk-slave-restart - Watch and restart MySQL replication after errors.

SYNOPSIS

  mk-slave-restart --verbose
 
 

DESCRIPTION

mk-slave-restart watches one or more MySQL replication slaves and tries to skip statements that cause errors. It polls slaves intelligently with an exponentially varying sleep time. You can specify errors to skip and run the slaves until a certain binlog position.

Note: it has come to my attention that Yahoo! had or has an internal tool called fix_repl, described to me by a past Yahoo! employee and mentioned in the first edition of High Performance MySQL. Apparently this tool does the same thing. Make no mistake, though: this is not a way to ``fix replication.'' In fact I would not even encourage its use on a regular basis; I use it only when I have an error I know I just need to skip past.

Indiscriminate use of this tool can easily screw up a server you might have had a chance to truly fix. You have been warned.

DOWNLOADING

You can download Maatkit from Google Code at <http://code.google.com/p/maatkit/>, or you can get any of the tools easily with a command like the following:

    wget http://www.maatkit.org/get/toolname
    or
    wget http://www.maatkit.org/trunk/toolname
 
 

Where "toolname" can be replaced with the name (or fragment of a name) of any of the Maatkit tools. Once downloaded, they're ready to run; no installation is needed. The first URL gets the latest released version of the tool, and the second gets the latest trunk code from Subversion.

OPTIONS

--always

Start slaves even when no error.

Always (re)start the slave processes, even when there is no error. With this option enabled, "mk-slave-restart" will not let you stop the slave if you want to!

--askpass

Prompt for a password when connecting to MySQL.

--charset

short form: -A; type: string

Default character set.

Enables character set settings in Perl and MySQL. If the value is "utf8", sets Perl's binmode on STDOUT to utf8, passes the "mysql_enable_utf8" option to DBD::mysql, and runs "SET NAMES UTF8" after connecting to MySQL. Any other value sets binmode on STDOUT without the utf8 layer, and runs "SET NAMES" after connecting to MySQL.

--daemonize

Fork to background and detach (POSIX only).

This probably doesn't work on Microsoft Windows.

--database

short form: -D; type: string

Database to use.

--defaults-file

short form: -F; type: string

Only read mysql options from the given file.

--error-length

short form: -L; type: int

Max length of error message to print.

When ``--verbose'' is set high enough to print the error, this option will truncate the error text to the specified length. This can be useful to prevent wrapping on the terminal.

--error-numbers

short form: -e; type: int

Only restart this comma-separated list of errors.

Makes mk-slave-restart only try to restart if the error number is in this comma-separated list of errors. If it sees an error not in the list, it will exit.

The error number is in the "last_errno" column of "SHOW SLAVE STATUS".

--error-text

short form: -E; type: string

Only restart errors that match this pattern.

A Perl regular expression against which the error text, if any, is matched. If the error text exists and matches, mk-slave-restart will try to restart the slave. If it exists but doesn't match, mk-slave-restart will exit.

The error text is in the "last_error" column of "SHOW SLAVE STATUS".

--host

short form: -h; type: string

Connect to host.

--maxsleep

short form: -M; type: float; default: 64

Maximum sleep seconds.

The maximum time mk-slave-restart will sleep before polling the slave again. See ``SLEEP''.

--minsleep

short form: -m; type: float; default: 0.015625

The minimum time mk-slave-restart will sleep before polling the slave again. See ``SLEEP''.

--monitor

default: yes

Whether to monitor the slave.

Unless you specify --monitor explicitly, ``--stop'' will disable it.

--password

short form: -p; type: string

Password to use when connecting.

--pid

type: string

Create the given PID file when daemonized.

For example, '--daemonize --pid /tmp/mk-slave-restart.pid' would cause mk-slave-restart to create the PID file /tmp/mk-slave-restart.pid.

/var/run/ is usually not writable by non-root users, therefore /tmp/ is a more reliable alternative.

The PID file is removed when the daemonized instance of mk-slave-restart exits.

--port

short form: -P; type: int

Port number to use for connection.

--quiet

short form: -q

Suppresses normal output (disables ``--verbose'').

--recurse

short form: -r; type: int; default: 0

Number of levels to recurse.

This option specifies that instead of just watching the server specified on the command-line, "mk-slave-restart" should try to find its slaves and watch them too, up to the specified depth. The default depth of 0 means ``just watch the slave specified.''

This works if you have configured your slaves to show up in "SHOW SLAVE HOSTS". The minimal configuration for this is the "report_host" parameter, but there are other ``report'' parameters as well for the port, username, and password.

If "SHOW SLAVE HOSTS" doesn't return anything, "mk-slave-restart" examines "SHOW PROCESSLIST" and tries to determine which connections are from slaves, then connect to them. This is less likely to work than "SHOW SLAVE HOSTS", but it works sometimes when that doesn't.

Recursion works by finding all slaves when the program starts, then watching them. If there is more than one slave, "mk-slave-restart" uses "fork()" to monitor them.

--sentinel

type: string; default: /tmp/mk-slave-restart-sentinel

Exit if this file exists.

--setvars

type: string; default: wait_timeout=10000

Set these MySQL variables.

Specify any variables you want to be set immediately after connecting to MySQL. These will be included in a "SET" command.

--skipcount

short form: -k; type: int; default: 1

Number of statements to skip when restarting the slave.

--sleep

short form: -s; type: int; default: 1

Initial sleep seconds between checking the slave.

See ``SLEEP''.

--socket

short form: -S; type: string

Socket file to use for connection.

--stop

Stop running instances by creating the sentinel file.

Causes "mk-slave-restart" to create the sentinel file specified by ``--sentinel''. This should have the effect of stopping all running instances which are watching the same sentinel file. If ``--monitor'' isn't specified, "mk-slave-restart" will exit after creating the file. If it is specified, "mk-slave-restart" will wait the interval given by ``--maxsleep'', then remove the file and continue working.

You might find this handy to stop cron jobs gracefully if necessary, or to replace one running instance with another. For example, if you want to stop and restart "mk-slave-restart" every hour (just to make sure that it is restarted every hour, in case of a server crash or some other problem), you could use a "crontab" line like this:

  0 * * * * mk-slave-restart --monitor --stop --sentinel /tmp/mk-slave-restartup
 
 

The non-default ``--sentinel'' will make sure the hourly "cron" job stops only instances previously started with the same options (that is, from the same "cron" job).

See also ``--sentinel''.

--time

short form: -t; type: time

Time to run before exiting.

Causes "mk-slave-restart" to stop after the specified time has elapsed. Optional suffix: s=seconds, m=minutes, h=hours, d=days; if no suffix, s is used.

--untilmaster

type: string

Run until this master log file and position.

Start the slave, and retry if it fails, until it reaches the given replication coordinates. The coordinates are the logfile and position on the master, given by relay_master_log_file, exec_master_log_pos. The argument must be in the format ``file,pos''. Separate the filename and position with a single comma and no space.

This will also cause an UNTIL clause to be given to START SLAVE.

After reaching this point, the slave should be stopped and mk-slave-restart will exit.

--untilrelay

type: string

Run until this relay log file and position.

Like ``--untilmaster'', but in the slave's relay logs instead. The coordinates are given by relay_log_file, relay_log_pos.

--user

short form: -u; type: string

User for login if not current user.

--verbose

short form: -v; cumulative: yes; default: 1

Be verbose; can specify multiple times.

Verbosity 1 outputs connection information, a timestamp, relay_log_file, relay_log_pos, and last_errno.

Verbosity 2 adds last_error. See also ``--error-length''.

Verbosity 3 prints the current sleep time each time mk-slave-restart sleeps.

SYSTEM REQUIREMENTS

You need Perl, DBI, DBD::mysql, and some core packages that ought to be installed in any reasonably new version of Perl.

OUTPUT

If you specify --verbose, mk-slave-restart prints a line every time it sees the slave has an error. See ``--verbose'' for details.

SLEEP

mk-slave-restart sleeps intelligently between polling the slave. The current sleep time varies.

•

The initial sleep time is given by ``--sleep''.

•

If it checks and finds an error, it halves the previous sleep time.

•

If it finds no error, it doubles the previous sleep time.

•

The sleep time is bounded below by ``--minsleep'' and above by ``--maxsleep''.

•

Immediately after finding an error, mk-slave-restart assumes another error is very likely to happen next, so it sleeps the current sleep time or the initial sleep time, whichever is less.

EXIT STATUS

Successful exit status is 0. Any other value represents the exit status of the Perl process itself, or of the last forked process that exited if there were multiple servers to monitor.

COMPATIBILITY

mk-slave-restart should work on many versions of MySQL. Lettercase of many output columns from SHOW SLAVE STATUS has changed over time, so it treats them all as lowercase.

ENVIRONMENT

The environment variable "MKDEBUG" enables verbose debugging output in all of the Maatkit tools:

    MKDEBUG=1 mk-....
 
 

When ``--daemonize'' is given and this variable is set, output is directed to a debug file in "/tmp".

BUGS

Please use Google Code Issues and Groups to report bugs or request support: <http://code.google.com/p/maatkit/>.

Please include the complete command-line used to reproduce the problem you are seeing, the version of all MySQL servers involved, the complete output of the tool when run with ``--version'', and if possible, debugging output produced by running with the "MKDEBUG=1" environment variable.

SEE ALSO

See also mk-table-checksum, mk-table-sync, mk-slave-delay.

COPYRIGHT, LICENSE AND WARRANTY

This program is copyright 2007-2008 Baron Schwartz. Feedback and improvements are welcome.

THIS PROGRAM IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2; OR the Perl Artistic License. On UNIX and similar systems, you can issue `man perlgpl' or `man perlartistic' to read these licenses.

You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.

AUTHOR

Baron Schwartz

VERSION

This manual page documents Ver 1.0.10 Distrib 2725 $Revision: 2311 $.