Man page for mk-slave-restart

August 24, 2007 – 5:32 pm

MK-SLAVE-RESTART

Section: User Contributed Perl Documentation (1)
Updated: 2008-06-01
Index
Return to Main Contents

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 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

–always

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.

–daemonize

Fork to the background and detach from the shell. This probably doesn’t work
on Microsoft Windows.

–charset

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.

–database

Database to use.

–defaults-file

Only read default options from the given file.

–error-numbers

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

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".

–error-length

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.

–help

Show a brief help message and exit.

–host

Connect to host.

–maxsleep

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

–minsleep

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

–monitor

Whether to monitor the slave. The default is true, but unless you specify it
explicitly, “–stop” will disable it by default.

–password

Password to use when connecting.

–port

Port number to use for connection.

–quiet

Disables “–verbose”.

–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

The presence of the file specified by “–sentinel” will cause
"mk-slave-restart" to stop and exit. The default is
"/tmp/mk-slave-restart-sentinel".

–setvars

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

–skipcount

The number of statements to skip when restarting the slave.

–sleep

The initial sleep time between checking the slave. See “SLEEP”.

–socket

Socket file to use for connection.

–stop

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).

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

If you find bugs, need features, etc please use the bug tracker, forums, and
mailing lists at 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 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 1.0.7 Distrib 1972 $Revision: 1970 $.

Index

NAME
SYNOPSIS
DESCRIPTION
DOWNLOADING
OPTIONS
SYSTEM REQUIREMENTS
OUTPUT
SLEEP
EXIT STATUS
COMPATIBILITY
ENVIRONMENT
BUGS
SEE ALSO
COPYRIGHT, LICENSE AND WARRANTY
AUTHOR
VERSION

Linux Apache MySQL PHP Tips