MK-SLAVE-DELAY(1)

NAME
mk-slave-delay - Make a MySQL slave server lag behind its master.

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

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

DESCRIPTION
"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".

Note that since "mk-slave-delay" starts and stops the SQL thread, monitoring systems may think the slave is having trouble when it's just being held back intentionally.

The slave host can be specified using one of two methods. The first method is to use at least one of the standard connection-related command line options: "--defaults-file", "--password", "--host", "--port", "--socket" or "--user". These options only apply to the slave host. To connect to a slave host using this method while also specifying an optional master host on the command line requires that the master host be specified using the next method, a DSN.

The second method to specifiy the slave host, or an optional master host, is a DSN. A DSN is a special syntax that can be either just a hostname (like "server.domain.com" or 1.2.3.4), or a "key=value,key=value" string. Keys are a single letter:

   KEY MEANING
   === =======
   h   Connect to host
   P   Port number to use for connection
   S   Socket file to use for connection
   u   User for login if not current user
   p   Password to use when connecting
   F   Only read default options from the given file

If you omit any values in a MASTER-HOST DSN, they are filled in with defaults 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.

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

--ask-pass
    Prompt for a password when connecting to MySQL.

--charset
    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.

--config
    type: Array

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

--[no]continue
    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.

--daemonize
    Fork to the background and detach from the shell. POSIX operating systems only.

--defaults-file
    short form: -F; type: string

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

--delay
    type: time; default: 1h

    How far the slave should lag its master.

--help
    Show help and exit.

--host
    short form: -h; type: string

    Connect to host.

--interval
    type: time; default: 1m

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

--log
    type: string

    Print all output to this file when daemonized.

--password
    short form: -p; type: string

    Password to use when connecting.

--pid
    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.

--port
    short form: -P; type: int

    Port number to use for connection.

--quiet
    short form: -q

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

--run-time
    type: time

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

--set-vars
    type: string; default: wait_timeout=10000

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

--socket
    short form: -S; type: string

    Socket file to use for connection.

--use-master
    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.

--user
    short form: -u; type: string

    User for login if not current user.

--version
    Show version and exit.

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 "--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.

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

   MKDEBUG=1 mk-....

BUGS
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 2007-2009 Sergey Zhuravlev and 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
Sergey Zhuravlev and Baron Schwartz.

VERSION
This manual page documents Ver 1.0.15 Distrib 4047 $Revision: 4045 $.