mk-slave-delay(1) Make a MySQL slave server lag behind its master.


To hold slavehost one minute behind its master for ten minutes:

mk-slave-delay --delay 1m --interval 15s --run-time 10m slavehost


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-delay is generally very low-risk. It simply starts and stops the replication SQL thread. This might cause monitoring systems to think the slave is having trouble.

At the time of this release, mk-slave-delay does not reconnect to the server if the connection is lost.

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: <>.

See also ``BUGS'' for more information on filing bugs and getting help.


"mk-slave-delay" watches a slave and starts and stops its replication SQL thread as necessary to hold it at least as far behind the master as you request. In practice, it will typically cause the slave to lag between ``--delay'' and ``--delay''+``--interval'' behind the master.

It bases the delay on binlog positions in the slave's relay logs by default, so there is no need to connect to the master. This works well if the IO thread doesn't lag the master much, which is typical in most replication setups; the IO thread lag is usually milliseconds on a fast network. If your IO thread's lag is too large for your purposes, "mk-slave-delay" can also connect to the master for information about binlog positions.

If the slave's I/O thread reports that it is waiting for the SQL thread to free some relay log space, "mk-slave-delay" will automatically connect to the master to find binary log positions. If ``--ask-pass'' and ``--daemonize'' are given, it is possible that this could cause it to ask for a password while daemonized. In this case, it exits. Therefore, if you think your slave might encounter this condition, you should be sure to either specify ``--use-master'' explicitly when daemonizing, or don't specify ``--ask-pass''.

The SLAVE-HOST and optional MASTER-HOST are both DSNs. See ``DSN OPTIONS''. Missing MASTER-HOST values are filled in with values from SLAVE-HOST, so you don't need to specify them in both places. "mk-slave-delay" reads all normal MySQL option files, such as ~/.my.cnf, so you may not need to specify username, password and other common options at all.

"mk-slave-delay" tries to exit gracefully by trapping signals such as Ctrl-C. You cannot bypass ``--[no]continue'' with a trappable signal.


mk-slave-delay requires the following privileges: PROCESS, REPLICATION CLIENT, and SUPER.


If you specify ``--quiet'', there is no output. Otherwise, the normal output is a status message consisting of a timestamp and information about what "mk-slave-delay" is doing: starting the slave, stopping the slave, or just observing.


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.

type: Array

Read this comma-separated list of config files; if specified, this must be the first option on the command line.

default: yes

Continue replication normally on exit. After exiting, restart the slave's SQL thread with no UNTIL condition, so it will run as usual and catch up to the master. This is enabled by default and works even if you terminate "mk-slave-delay" with Control-C.

Fork to the background and detach from the shell. POSIX operating systems only.
short form: -F; type: string

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

type: time; default: 1h

How far the slave should lag its master.

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

Connect to host.

type: time; default: 1m

How frequently "mk-slave-delay" should check whether the slave needs to be started or stopped.

type: string

Print all output to this file when daemonized.

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

Don't print informational messages about operation. See OUTPUT for details.

type: time

How long "mk-slave-delay" should run before exiting. The default is to run forever.

type: string; default: wait_timeout=10000

Set these MySQL variables. Immediately after connecting to MySQL, this string will be appended to SET and executed.

short form: -S; type: string

Socket file to use for connection.

Get binlog positions from master, not slave. Don't trust the binlog positions in the slave's relay log. Connect to the master and get binlog positions instead. If you specify this option without giving a MASTER-HOST on the command line, "mk-slave-delay" examines the slave's SHOW SLAVE STATUS to determine the hostname and port for connecting to the master.

"mk-slave-delay" uses only the MASTER_HOST and MASTER_PORT values from SHOW SLAVE STATUS for the master connection. It does not use the MASTER_USER value. If you want to specify a different username for the master than the one you use to connect to the slave, you should specify the MASTER-HOST option explicitly on the command line.

short form: -u; type: string

User for login if not current user.

Show version and exit.


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.
  • A

    dsn: charset; copy: yes

    Default character set.

  • D

    dsn: database; copy: yes

    Default database.

  • F

    dsn: mysql_read_default_file; copy: yes

    Only read default options from the given file

  • h

    dsn: host; copy: yes

    Connect to host.

  • p

    dsn: password; copy: yes

    Password to use when connecting.

  • P

    dsn: port; copy: yes

    Port number to use for connection.

  • S

    dsn: mysql_socket; copy: yes

    Socket file to use for connection.

  • u

    dsn: user; copy: yes

    User for login if not current user.


You can download Maatkit from Google Code at <>, or you can get any of the tools easily with a command like the following:


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-....


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


For list of known bugs see <>.

Please use Google Code Issues and Groups to report bugs or request support: <>. 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.


This program is copyright 2007-2010 Sergey Zhuravlev and 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.


Sergey Zhuravlev, Baron Schwartz


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 1.0.21 Distrib 6652 $Revision: 6645 $.