Man page for mk-slave-delay

August 24, 2007 – 5:31 pm

MK-SLAVE-DELAY

Section: User Contributed Perl Documentation (1)
Updated: 2008-06-01
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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 –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 “–askpass” 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
“–usemaster” explicitly when daemonizing, or don’t specify “–askpass”.

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.

There is a special syntax for connecting to MySQL servers. Each server name
on the command line can be either just a hostname, 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 MASTER-HOST, 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 “–continue” with a trappable signal.

DOWNLOADING

You can download Maatkit from the Sourceforge website at
<http://sourceforge.net/projects/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

–askpass

Prompt for a password when connecting to MySQL.

–continue

short form: -c; negatable: yes; 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. POSIX only.

–delay

short form: -d; type: time; default: 1h

How far the slave should lag its master.

–interval

short form: -i; type: time; default: 1m

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

–quiet

short form: -q

Do not output regular status messages.

–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.

–time

short form: -t; type: time

How long "mk-slave-delay" should run before exiting.

Default is to run forever.

–usemaster

short form: -u

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.

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 the Sourceforge bug tracker, forums, and mailing lists to request
support or report bugs: <http://sourceforge.net/projects/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 (c) 2007 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 1.0.7 Distrib 1972 $Revision: 1970 $.

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