mk-slave-restart.1p man page

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


Usage: mk-slave-restart [OPTION...] [DSN]

mk-slave-restart watches one or more MySQL replication slaves for errors, and tries to restart replication if it stops.


The following section is included to inform users about the potential risks, whether known or unknown, of using this tool. The two main categories of risks are those created by the nature of the tool (e.g. read-only tools vs. read-write tools) and those created by bugs.

mk-slave-restart is a brute-force way to try to keep a slave server running when it is having problems with replication. Don't be too hasty to use it unless you need to. If you use this tool carelessly, you might miss the chance to really solve the slave server's problems.

At the time of this release there is a bug that causes an invalid "CHANGE MASTER TO" statement to be executed.

The authoritative source for updated information is always the online issue tracking system. Issues that affect this tool will be marked as such. You can see a list of such issues at the following URL: <http://www.maatkit.org/bugs/mk-slave-re…>.

See also "Bugs" for more information on filing bugs and getting help.


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.


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


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 "--min-sleep" and above by "--max-sleep".
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

An exit status of 0 (sometimes also called a return value or return code) indicates success. 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.


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.


This tool accepts additional command-line arguments. Refer to the "Synopsis" and usage information for details.

Start slaves even when there is no error. With this option enabled, mk-slave-restart will not let you stop the slave manually if you want to!
Prompt for a password when connecting to MySQL.
short form: -A; type: string

Default character set. 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.
default: yes

Check the last relay log file and position before checking for slave errors.

By default mk-slave-restart will not doing anything (it will just sleep) if neither the relay log file nor the relay log position have changed since the last check. This prevents infinite loops (i.e. restarting the same error in the same relay log file at the same relay log position).

For certain slave errors, however, this check needs to be disabled by specifying "--no-check-relay-log". Do not do this unless you know what you are doing!
type: Array

Read this comma-separated list of config files; if specified, this must be the first option on the command line.
Fork to the background and detach from the shell. POSIX operating systems only.
short form: -D; type: string

Database to use.
short form: -F; type: string

Only read mysql options from the given file. You must give an absolute pathname.
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.
type: hash

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".
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".
Show help and exit.
short form: -h; type: string

Connect to host.
type: string

Print all output to this file when daemonized.
type: float; default: 64

Maximum sleep seconds.

The maximum time mk-slave-restart will sleep before polling the slave again. This is also the time that mk-slave-restart will wait for all other running instances to quit if both "--stop" and "--monitor" are specified.

See "Sleep".
type: float; default: 0.015625

The minimum time mk-slave-restart will sleep before polling the slave again. See "Sleep".
Whether to monitor the slave (default). Unless you specify --monitor explicitly, "--stop" will disable it.
short form: -p; type: string

Password to use when connecting.
type: string

Create the given PID file when daemonized. The file contains the process ID of the daemonized instance. The PID file is removed when the daemonized instance exits. The program checks for the existence of the PID file when starting; if it exists and the process with the matching PID exists, the program exits.
short form: -P; type: int

Port number to use for connection.
short form: -q

Suppresses normal output (disables "--verbose").
type: int; default: 0

Watch slaves of the specified server, up to the specified number of servers deep in the hierarchy. The default depth of 0 means "just watch the slave specified."

mk-slave-restart examines "SHOW PROCESSLIST" and tries to determine which connections are from slaves, then connect to them. See "--recursion-method".

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.

This also 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.

type: string

Preferred recursion method used to find slaves.

Possible methods are:

===========  ================
hosts        SHOW SLAVE HOSTS

The processlist method is preferred because SHOW SLAVE HOSTS is not reliable. However, the hosts method is required if the server uses a non-standard port (not 3306). Usually mk-slave-restart does the right thing and finds the slaves, but you may give a preferred method and it will be used first. If it doesn't find any slaves, the other methods will be tried.

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

Exit if this file exists.
type: string; default: wait_timeout=10000

Set these MySQL variables. Immediately after connecting to MySQL, this string will be appended to SET and executed.
type: int; default: 1

Number of statements to skip when restarting the slave.
type: int; default: 1

Initial sleep seconds between checking the slave.

See "Sleep".
short form: -S; type: string

Socket file to use for connection.

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 "--max-sleep", 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".

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.
type: string

Run until this relay log file and position. Like "--until-master", but in the slave's relay logs instead. The coordinates are given by relay_log_file, relay_log_pos.
short form: -u; type: string

User for login if not current user.
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.
Show version and exit.

Dsn Options

These DSN options are used to create a DSN. Each option is given like "option=value". The options are case-sensitive, so P and p are not the same option. There cannot be whitespace before or after the "=" and if the value contains whitespace it must be quoted. DSN options are comma-separated. See the maatkit manpage for full details.


dsn: charset; copy: yes

Default character set.

dsn: database; copy: yes

Default database.

dsn: mysql_read_default_file; copy: yes

Only read default options from the given file

dsn: host; copy: yes

Connect to host.

dsn: password; copy: yes

Password to use when connecting.

dsn: port; copy: yes

Port number to use for connection.

dsn: mysql_socket; copy: yes

Socket file to use for connection.

dsn: user; copy: yes

User for login if not current user.


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
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.


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".

System Requirements

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


For a list of known bugs see <http://www.maatkit.org/bugs/mk-slave-re…>.

Please use Google Code Issues and Groups to report bugs or request support: <http://code.google.com/p/maatkit/>. You can also join #maatkit on Freenode to discuss 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.

Copyright, License and Warranty

This program is copyright 2007-2011 Baron Schwartz. Feedback and improvements are welcome.


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.

See Also

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


Baron Schwartz

About Maatkit

This tool is part of Maatkit, a toolkit for power users of MySQL. Maatkit was created by Baron Schwartz; Baron and Daniel Nichter are the primary code contributors. Both are employed by Percona. Financial support for Maatkit development is primarily provided by Percona and its clients.


This manual page documents Ver 1.0.22 Distrib 7540 $Revision: 7531 $.