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mk-log-player.1p - Man Page

Replay MySQL query logs.


Usage: mk-log-player [OPTION...] [DSN]

mk-log-player splits and plays slow log files.

Split slow.log on Thread_id into 16 session files, save in ./sessions:

  mk-log-player --split Thread_id --session-files 16 --base-dir ./sessions slow.log

Play all those sessions on host1, save results in ./results:

  mk-log-player --play ./sessions --base-dir ./results h=host1

Use mk-query-digest to summarize the results:

  mk-query-digest ./results/*


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.

This tool is meant to load a server as much as possible, for stress-testing purposes.  It is not designed to be used on production servers.

At the time of this release there is a bug which causes mk-log-player to exceed max open files during "--split".

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-log-player>.

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


mk-log-player does two things: it splits MySQL query logs into session files and it plays (executes) queries in session files on a MySQL server.  Only session files can be played; slow logs cannot be played directly without being split.

A session is a group of queries from the slow log that all share a common attribute, usually Thread_id.  The common attribute is specified with "--split".  Multiple sessions are saved into a single session file. See "--session-files", "--max-sessions", "--base-file-name" and "--base-dir".  These session files are played with "--play".

mk-log-player will "--play" session files in parallel using N number of "--threads".  (They're not technically threads, but we call them that anyway.)  Each thread will play all the sessions in its given session files. The sessions are played as fast as possible--there are no delays--because the goal is to stress-test and load-test the server.  So be careful using this script on a production server!

Each "--play" thread writes its results to a separate file.  These result files are in slow log format so they can be aggregated and summarized with mk-query-digest.  See "Output".


Both "--split" and "--play" have two outputs: status messages printed to STDOUT to let you know what the script is doing, and session or result files written to separate files saved in "--base-dir".  You can suppress all output to STDOUT for each with "--quiet", or increase output with "--verbose".

The session files written by "--split" are simple text files containing queries grouped into sessions.  For example:


  use foo

  SELECT col FROM foo_tbl

The format of these session files is important: each query must be a single line separated by a single blank line.  And the "-- START SESSION" comment tells mk-log-player where individual sessions begin and end so that "--play" can correctly fake Thread_id in its result files.

The result files written by "--play" are in slow log format with a minimal header: the only attributes printed are Thread_id, Query_time and Schema.


Specify at least one of "--play", "--split" or "--split-random".

"--play" and "--split" are mutually exclusive.

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


group: Play

Prompt for a password when connecting to MySQL.


type: string; default: ./

Base directory for "--split" session files and "--play" result file.


type: string; default: session

Base file name for "--split" session files and "--play" result file.

Each "--split" session file will be saved as <base-file-name>-N.txt, where N is a four digit, zero-padded session ID.  For example: session-0003.txt.

Each "--play" result file will be saved as <base-file-name>-results-PID.txt, where PID is the process ID of the executing thread.

All files are saved in "--base-dir".


short form: -A; type: string; group: Play

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.


short form: -F; type: string

Only read mysql options from the given file.


Print which processes play which session files then exit.


type: string; group: Split

Discard "--split" events for which this Perl code doesn't return true.

This option only works with "--split".

This option allows you to inject Perl code into the tool to affect how the tool runs.  Usually your code should examine $event to decided whether or not to allow the event.  $event is a hashref of attributes and values of the event being filtered.  Or, your code could add new attribute-value pairs to $event for use by other options that accept event attributes as their value.  You can find an explanation of the structure of $event at <http://code.google.com/p/maatkit/wiki/EventAttributes>.

There are two ways to supply your code: on the command line or in a file. If you supply your code on the command line, it is injected into the following subroutine where $filter is your code:

   sub {
      MKDEBUG && _d('callback: filter');
      my( $event ) = shift;
      ( $filter ) && return $event;

Therefore you must ensure two things: first, that you correctly escape any special characters that need to be escaped on the command line for your shell, and two, that your code is syntactically valid when injected into the subroutine above.

Here's an example filter supplied on the command line that discards events that are not SELECT statements:

  --filter '$event->{arg} =~ m/^select/i'

The second way to supply your code is in a file.  If your code is too complex to be expressed on the command line that results in valid syntax in the subroutine above, then you need to put the code in a file and give the file name as the value to "--filter".  The file should not contain a shebang (#!/usr/bin/perl) line.  The entire contents of the file is injected into the following subroutine:

   sub {
      MKDEBUG && _d('callback: filter');
      my( $event ) = shift;
      $filter && return $event;

That subroutine is almost identical to the one above except your code is not wrapped in parentheses.  This allows you to write multi-line code like:

   my $event_ok;
   if (...) {
      $event_ok = 1;
   else {
      $event_ok = 0;

Notice that the last line is not syntactically valid by itself, but it becomes syntactically valid when injected into the subroutine because it becomes:

   $event_ok && return $event;

If your code doesn't compile, the tool will die with an error.  Even if your code compiles, it may crash to tool during runtime if, for example, it tries a pattern match an undefined value.  No safeguards of any kind of provided so code carefully!


Show help and exit.


short form: -h; type: string; group: Play

Connect to host.


type: int; default: 1; group: Play

How many times each thread should play all its session files.


type: int; default: 5000000; group: Split

Maximum number of sessions to "--split".

By default, mk-log-player tries to split every session from the log file. For huge logs, however, this can result in millions of sessions.  This option causes only the first N number of sessions to be saved.  All sessions after this number are ignored, but sessions split before this number will continue to have their queries split even if those queries appear near the end of the log and after this number has been reached.


group: Play

Play only SELECT and USE queries; ignore all others.


short form: -p; type: string; group: Play

Password to use when connecting.


type: string

Create the given PID file.  The file contains the process ID of the script. The PID file is removed when the script exits.  Before starting, the script checks if the PID file already exists.  If it does not, then the script creates and writes its own PID to it.  If it does, then the script checks the following: if the file contains a PID and a process is running with that PID, then the script dies; or, if there is no process running with that PID, then the script overwrites the file with its own PID and starts; else, if the file contains no PID, then the script dies.


type: string; group: Play

Play (execute) session files created by "--split".

The argument to play must be a comma-separated list of session files created by "--split" or a directory.  If the argument is a directory, ALL files in that directory will be played.


short form: -P; type: int; group: Play

Port number to use for connection.


group: Play

Print queries instead of playing them; requires "--play".

You must also specify "--play" with "--print".  Although the queries will not be executed, "--play" is required to specify which session files to read.


short form: -q

Do not print anything; disables "--verbose".


default: yes

Print "--play" results to files in "--base-dir".


type: int; default: 8; group: Split

Number of session files to create with "--split".

The number of session files should either be equal to the number of "--threads" you intend to "--play" or be an even multiple of "--threads".  This number is important for maximum performance because it:
 * allows each thread to have roughly the same amount of sessions to play
 * avoids having to open/close many session files
 * avoids disk IO overhead by doing large sequential reads

You may want to increase this number beyond "--threads" if each session file becomes too large.  For example, splitting a 20G log into 8 sessions files may yield roughly eight 2G session files.

See also "--max-sessions".


type: string; group: Play; 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; group: Play

Socket file to use for connection.


type: string; group: Split

Split log by given attribute to create session files.

Valid attributes are any which appear in the log: Thread_id, Schema, etc.


group: Split

Split log without an attribute, write queries round-robin to session files.

This option, if specified, overrides "--split" and causes the log to be split query-by-query, writing each query to the next session file in round-robin style.  If you don't care about "sessions" and just want to split a lot into N many session files and the relation or order of the queries does not matter, then use this option.


type: int; default: 2; group: Play

Number of threads used to play sessions concurrently.

Specifies the number of parallel processes to run.  The default is 2.  On GNU/Linux machines, the default is the number of times 'processor' appears in /proc/cpuinfo.  On Windows, the default is read from the environment. In any case, the default is at least 2, even when there's only a single processor.

See also "--session-files".


type: string; group: Split

The type of log to "--split" (default slowlog).  The permitted types are


Split the output of running mysqlbinlog against a binary log file. Currently, splitting binary logs does not always work well depending on what the binary logs contain.  Be sure to check the session files after splitting to ensure proper "Output".

If the binary log contains row-based replication data, you need to run mysqlbinlog with options --base64-output=decode-rows --verbose, else invalid statements will be written to the session files.


Split a general log file.


Split a log file in any variation of MySQL slow-log format.


short form: -u; type: string; group: Play

User for login if not current user.


short form: -v; cumulative: yes; default: 0

Increase verbosity; can be specified multiple times.

This option is disabled by "--quiet".


Show version and exit.


type: array; default: 0; group: Play

Not implemented yet.

The wait time is given in seconds with microsecond precision and can be either a single value or a range.  A single value causes an exact wait; example: 0.010 = wait 10 milliseconds.  A range causes a random wait between the given value times; example: 0.001,1 = random wait from 1 millisecond to 1 second.


default: no; group: Play

Print warnings about SQL errors such as invalid queries to STDERR.

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.


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-....

System Requirements

You need Perl 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-log-player>.

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 2008-2011 Percona Inc. 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.


Daniel Nichter

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 1.0.9 Distrib 7540 $Revision: 7531 $.


2024-01-25 perl v5.38.2 User Contributed Perl Documentation