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




pt-slave-delay starts and stops a slave server as needed to make it lag behind the master. The SLAVE_DSN and MASTER_DSN use DSN syntax, and values are copied from the SLAVE_DSN to the MASTER_DSN if omitted.

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

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


Percona Toolkit is mature, proven in the real world, and well tested, but all database tools can pose a risk to the system and the database server. Before using this tool, please:

  • Read the tool’s documentation
  • Review the tool’s known “BUGS”
  • Test the tool on a non-production server
  • Backup your production server and verify the backups


pt-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, pt-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, pt-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_DSN and optional MASTER_DSN are both DSNs. See “DSN OPTIONS”. Missing MASTER_DSN values are filled in with values from SLAVE_DSN, so you don’t need to specify them in both places. pt-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.

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


pt-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 pt-slave-delay is doing: starting the slave, stopping the slave, or just observing.


This tool accepts additional command-line arguments. Refer to the “SYNOPSIS” and usage information for details.


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 pt-slave-delay with Control-C.


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


short form: -D; type: string

The database to use for the connection.


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 pt-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. If password contains commas they must be escaped with a backslash: “exam,ple”


type: string

Create the given PID file. The tool won’t start if the PID file already exists and the PID it contains is different than the current PID. However, if the PID file exists and the PID it contains is no longer running, the tool will overwrite the PID file with the current PID. The PID file is removed automatically when the tool 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 pt-slave-delay should run before exiting. The default is to run forever.


type: Array

Set the MySQL variables in this comma-separated list of variable=value pairs.

By default, the tool sets:


Variables specified on the command line override these defaults. For example, specifying --set-vars wait_timeout=500 overrides the defaultvalue of 10000.

The tool prints a warning and continues if a variable cannot be set.


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_DSN on the command line, pt-slave-delay examines the slave’s SHOW SLAVE STATUS to determine the hostname and port for connecting to the master.

pt-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_DSN option explicitly on the command line.


short form: -u; type: string

User for login if not current user.


Show version and exit.


default: yes

Check for the latest version of Percona Toolkit, MySQL, and other programs.

This is a standard “check for updates automatically” feature, with two additional features. First, the tool checks the version of other programs on the local system in addition to its own version. For example, it checks the version of every MySQL server it connects to, Perl, and the Perl module DBD::mysql. Second, it checks for and warns about versions with known problems. For example, MySQL 5.5.25 had a critical bug and was re-released as 5.5.25a.

Any updates or known problems are printed to STDOUT before the tool’s normal output. This feature should never interfere with the normal operation of the tool.

For more information, visit https://www.percona.com/version-check.


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 percona-toolkit 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. If password contains commas they must be escaped with a backslash: “exam,ple”

  • 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.


The environment variable PTDEBUG enables verbose debugging output to STDERR. To enable debugging and capture all output to a file, run the tool like:

PTDEBUG=1 pt-slave-delay ... > FILE 2>&1

Be careful: debugging output is voluminous and can generate several megabytes of output.


You need Perl, DBI, DBD::mysql, 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.percona.com/bugs/pt-slave-delay.

Please report bugs at https://bugs.launchpad.net/percona-toolkit. Include the following information in your bug report:

  • Complete command-line used to run the tool
  • Tool --version
  • MySQL version of all servers involved
  • Output from the tool including STDERR
  • Input files (log/dump/config files, etc.)

If possible, include debugging output by running the tool with PTDEBUG; see “ENVIRONMENT”.


Visit http://www.percona.com/software/percona-toolkit/ to download the latest release of Percona Toolkit. Or, get the latest release from the command line:

wget percona.com/get/percona-toolkit.tar.gz

wget percona.com/get/percona-toolkit.rpm

wget percona.com/get/percona-toolkit.deb

You can also get individual tools from the latest release:

wget percona.com/get/TOOL

Replace TOOL with the name of any tool.


Sergey Zhuravlev and Baron Schwartz


This tool is part of Percona Toolkit, a collection of advanced command-line tools for MySQL developed by Percona. Percona Toolkit was forked from two projects in June, 2011: Maatkit and Aspersa. Those projects were created by Baron Schwartz and primarily developed by him and Daniel Nichter. Visit http://www.percona.com/software/ to learn about other free, open-source software from Percona.


pt-slave-delay 2.2.16