pt-heartbeat

NAME

pt-heartbeat - Monitor MySQL replication delay.

SYNOPSIS

Usage

pt-heartbeat [OPTIONS] [DSN] --update|--monitor|--check|--stop

pt-heartbeat measures replication lag on a MySQL or PostgreSQL server. You can use it to update a master or monitor a replica. If possible, MySQL connection options are read from your .my.cnf file.

Start daemonized process to update test.heartbeat table on master:

pt-heartbeat -D test --update -h master-server --daemonize

Monitor replication lag on slave:

pt-heartbeat -D test --monitor -h slave-server

pt-heartbeat -D test --monitor -h slave-server --dbi-driver Pg

Check slave lag once and exit (using optional DSN to specify slave host):

pt-heartbeat -D test --check h=slave-server

RISKS

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

DESCRIPTION

pt-heartbeat is a two-part MySQL and PostgreSQL replication delay monitoring system that measures delay by looking at actual replicated data. This avoids reliance on the replication mechanism itself, which is unreliable. (For example, SHOW SLAVE STATUS on MySQL).

The first part is an --update instance of pt-heartbeat that connects to a master and updates a timestamp (“heartbeat record”) every --interval seconds. Since the heartbeat table may contain records from multiple masters (see “MULTI-SLAVE HIERARCHY”), the server’s ID (@@server_id) is used to identify records.

The second part is a --monitor or --check instance of pt-heartbeat that connects to a slave, examines the replicated heartbeat record from its immediate master or the specified --master-server-id, and computes the difference from the current system time. If replication between the slave and the master is delayed or broken, the computed difference will be greater than zero and potentially increase if --monitor is specified.

You must either manually create the heartbeat table on the master or use --create-table. See --create-table for the proper heartbeat table structure. The MEMORY storage engine is suggested, but not required of course, for MySQL.

The heartbeat table must contain a heartbeat row. By default, a heartbeat row is inserted if it doesn’t exist. This feature can be disabled with the --[no]insert-heartbeat-row option in case the database user does not have INSERT privileges.

pt-heartbeat depends only on the heartbeat record being replicated to the slave, so it works regardless of the replication mechanism (built-in replication, a system such as Continuent Tungsten, etc). It works at any depth in the replication hierarchy; for example, it will reliably report how far a slave lags its master’s master’s master. And if replication is stopped, it will continue to work and report (accurately!) that the slave is falling further and further behind the master.

pt-heartbeat has a maximum resolution of 0.01 second. The clocks on the master and slave servers must be closely synchronized via NTP. By default, --update checks happen on the edge of the second (e.g. 00:01) and --monitor checks happen halfway between seconds (e.g. 00:01.5). As long as the servers’ clocks are closely synchronized and replication events are propagating in less than half a second, pt-heartbeat will report zero seconds of delay.

pt-heartbeat will try to reconnect if the connection has an error, but will not retry if it can’t get a connection when it first starts.

The --dbi-driver option lets you use pt-heartbeat to monitor PostgreSQL as well. It is reported to work well with Slony-1 replication.

MULTI-SLAVE HIERARCHY

If the replication hierarchy has multiple slaves which are masters of other slaves, like “master -> slave1 -> slave2”, --update instances can be ran on the slaves as well as the master. The default heartbeat table (see --create-table) is keyed on the server_id column, so each server will update the row where server_id=@@server_id.

For --monitor and --check, if --master-server-id is not specified, the tool tries to discover and use the slave’s immediate master. If this fails, or if you want monitor lag from another master, then you can specify the --master-server-id to use.

For example, if the replication hierarchy is “master -> slave1 -> slave2” with corresponding server IDs 1, 2 and 3, you can:

pt-heartbeat --daemonize -D test --update -h master
pt-heartbeat --daemonize -D test --update -h slave1

Then check (or monitor) the replication delay from master to slave2:

pt-heartbeat -D test --master-server-id 1 --check slave2

Or check the replication delay from slave1 to slave2:

pt-heartbeat -D test --master-server-id 2 --check slave2

Stopping the --update instance one slave1 will not affect the instance on master.

MASTER AND SLAVE STATUS

The default heartbeat table (see --create-table) has columns for saving information from SHOW MASTER STATUS and SHOW SLAVE STATUS. These columns are optional. If any are present, their corresponding information will be saved.

Percona XtraDB Cluster

Although pt-heartbeat should work with all supported versions of Percona XtraDB Cluster (PXC), we recommend using 5.5.28-23.7 and newer.

If you are setting up heartbeat instances between cluster nodes, keep in mind that, since the speed of the cluster is determined by its slowest node, pt-heartbeat will not report how fast the cluster itself is, but only how fast events are replicating from one node to another.

You must specify --master-server-id for --monitor and --check instances.

OPTIONS

Specify at least one of --stop, --update, --monitor, or --check.

--update, --monitor, and --check are mutually exclusive.

--daemonize and --check are mutually exclusive.

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

--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.

--check

Check slave delay once and exit. If you also specify --recurse, the tool will try to discover slave’s of the given slave and check and print their lag, too. The hostname or IP and port for each slave is printed before its delay. --recurse only works with MySQL.

--check-read-only

Check if the server has read_only enabled; If it does, the tool skips doing any inserts.

--config

type: Array

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

--create-table

Create the heartbeat --table if it does not exist.

This option causes the table specified by --database and --table to be created with the following MAGIC_create_heartbeat table definition:

CREATE TABLE heartbeat (
  ts                    varchar(26) NOT NULL,
  server_id             int unsigned NOT NULL PRIMARY KEY,
  file                  varchar(255) DEFAULT NULL,    -- SHOW MASTER STATUS
  position              bigint unsigned DEFAULT NULL, -- SHOW MASTER STATUS
  relay_master_log_file varchar(255) DEFAULT NULL,    -- SHOW SLAVE STATUS
  exec_master_log_pos   bigint unsigned DEFAULT NULL  -- SHOW SLAVE STATUS
);

The heartbeat table requires at least one row. If you manually create the heartbeat table, then you must insert a row by doing:

INSERT INTO heartbeat (ts, server_id) VALUES (NOW(), N);

or if using --utc:

INSERT INTO heartbeat (ts, server_id) VALUES (UTC_TIMESTAMP(), N);

where N is the server’s ID; do not use @@server_id because it will replicate and slaves will insert their own server ID instead of the master’s server ID.

This is done automatically by --create-table.

A legacy version of the heartbeat table is still supported:

CREATE TABLE heartbeat (
  id int NOT NULL PRIMARY KEY,
  ts datetime NOT NULL
);

Legacy tables do not support --update instances on each slave of a multi-slave hierarchy like “master -> slave1 -> slave2”. To manually insert the one required row into a legacy table:

INSERT INTO heartbeat (id, ts) VALUES (1, NOW());

or if using --utc:

INSERT INTO heartbeat (id, ts) VALUES (1, UTC_TIMESTAMP());

The tool automatically detects if the heartbeat table is legacy.

See also “MULTI-SLAVE HIERARCHY”.

--daemonize

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

--database

short form: -D; type: string

The database to use for the connection.

--dbi-driver

default: mysql; type: string

Specify a driver for the connection; mysql and Pg are supported.

--defaults-file

short form: -F; type: string

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

--file

type: string

Print latest --monitor output to this file.

When --monitor is given, prints output to the specified file instead of to STDOUT. The file is opened, truncated, and closed every interval, so it will only contain the most recent statistics. Useful when --daemonize is given.

--frames

type: string; default: 1m,5m,15m

Timeframes for averages.

Specifies the timeframes over which to calculate moving averages when --monitor is given. Specify as a comma-separated list of numbers with suffixes. The suffix can be s for seconds, m for minutes, h for hours, or d for days. The size of the largest frame determines the maximum memory usage, as up to the specified number of per-second samples are kept in memory to calculate the averages. You can specify as many timeframes as you like.

--help

Show help and exit.

--host

short form: -h; type: string

Connect to host.

--[no]insert-heartbeat-row

default: yes

Insert a heartbeat row in the --table if one doesn’t exist.

The heartbeat --table requires a heartbeat row, else there’s nothing to --update, --monitor, or --check! By default, the tool will insert a heartbeat row if one is not already present. You can disable this feature by specifying --no-insert-heartbeat-row in case the database user does not have INSERT privileges.

--interval

type: float; default: 1.0

How often to update or check the heartbeat --table. Updates and checks begin on the first whole second then repeat every --interval seconds for --update and every --interval plus --skew seconds for --monitor.

For example, if at 00:00.4 an --update instance is started at 0.5 second intervals, the first update happens at 00:01.0, the next at 00:01.5, etc. If at 00:10.7 a --monitor instance is started at 0.05 second intervals with the default 0.5 second --skew, then the first check happens at 00:11.5 (00:11.0 + 0.5) which will be --skew seconds after the last update which, because the instances are checking at synchronized intervals, happened at 00:11.0.

The tool waits for and begins on the first whole second just to make the interval calculations simpler. Therefore, the tool could wait up to 1 second before updating or checking.

The minimum (fastest) interval is 0.01, and the maximum precision is two decimal places, so 0.015 will be rounded to 0.02.

If a legacy heartbeat table (see --create-table) is used, then the maximum precision is 1s because the ts column is type datetime.

--log

type: string

Print all output to this file when daemonized.

--master-server-id

type: string

Calculate delay from this master server ID for --monitor or --check. If not given, pt-heartbeat attempts to connect to the server’s master and determine its server id.

--monitor

Monitor slave delay continuously.

Specifies that pt-heartbeat should check the slave’s delay every second and report to STDOUT (or if --file is given, to the file instead). The output is the current delay followed by moving averages over the timeframe given in --frames. For example,

5s [  0.25s,  0.05s,  0.02s ]
--password

short form: -p; type: string

Password to use when connecting.

--pid

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.

--port

short form: -P; type: int

Port number to use for connection.

--print-master-server-id

Print the auto-detected or given --master-server-id. If --check or --monitor is specified, specifying this option will print the auto-detected or given --master-server-id at the end of each line.

--recurse

type: int

Check slaves recursively to this depth in --check mode.

Try to discover slave servers recursively, to the specified depth. After discovering servers, run the check on each one of them and print the hostname (if possible), followed by the slave delay.

This currently works only with MySQL. See --recursion-method.

--recursion-method

type: array; default: processlist,hosts

Preferred recursion method used to find slaves.

Possible methods are:

METHOD       USES
===========  ==================
processlist  SHOW PROCESSLIST
hosts        SHOW SLAVE HOSTS
none         Do not find slaves

The processlist method is preferred because SHOW SLAVE HOSTS is not reliable. However, the hosts method is required if the server uses a non-standard port (not 3306). Usually pt-heartbeat does the right thing and finds the slaves, but you may give a preferred method and it will be used first. If it doesn’t find any slaves, the other methods will be tried.

--replace

Use REPLACE instead of UPDATE for –update.

When running in --update mode, use REPLACE instead of UPDATE to set the heartbeat table’s timestamp. The REPLACE statement is a MySQL extension to SQL. This option is useful when you don’t know whether the table contains any rows or not. It must be used in conjunction with –update.

--run-time

type: time

Time to run before exiting.

--sentinel

type: string; default: /tmp/pt-heartbeat-sentinel

Exit if this file exists.

--set-vars

type: Array

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

By default, the tool sets:

wait_timeout=10000

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.

--skew

type: float; default: 0.5

How long to delay checks.

The default is to delay checks one half second. Since the update happens as soon as possible after the beginning of the second on the master, this allows one half second of replication delay before reporting that the slave lags the master by one second. If your clocks are not completely accurate or there is some other reason you’d like to delay the slave more or less, you can tweak this value. Try setting the PTDEBUG environment variable to see the effect this has.

--socket

short form: -S; type: string

Socket file to use for connection.

--stop

Stop running instances by creating the sentinel file.

This should have the effect of stopping all running instances which are watching the same sentinel file. If none of --update, --monitor or --check is specified, pt-heartbeat will exit after creating the file. If one of these is specified, pt-heartbeat will wait the interval given by --interval, 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 pt-heartbeat 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 * * * * :program:`pt-heartbeat` --update -D test --stop \
  --sentinel /tmp/pt-heartbeat-hourly

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).

See also --sentinel.

--table

type: string; default: heartbeat

The table to use for the heartbeat.

Don’t specify database.table; use --database to specify the database.

See --create-table.

--update

Update a master’s heartbeat.

--user

short form: -u; type: string

User for login if not current user.

--utc

Ignore system time zones and use only UTC. By default pt-heartbeat does not check or adjust for different system or MySQL time zones which can cause the tool to compute the lag incorrectly. Specifying this option is a good idea because it ensures that the tool works correctly regardless of time zones.

If used, this option must be used for all pt-heartbeat instances: --update, --monitor, --check, etc. You should probably set the option in a --config file. Mixing this option with pt-heartbeat instances not using this option will cause false-positive lag readings due to different time zones (unless all your systems are set to use UTC, in which case this option isn’t required).

--version

Show version and exit.

--[no]version-check

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.

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 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.

  • 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.

ENVIRONMENT

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-heartbeat ... > FILE 2>&1

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

SYSTEM REQUIREMENTS

You need Perl, DBI, DBD::mysql, and some core packages that ought to be installed in any reasonably new version of Perl.

BUGS

For a list of known bugs, see http://www.percona.com/bugs/pt-heartbeat.

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”.

DOWNLOADING

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.

AUTHORS

Proven Scaling LLC, SixApart Ltd, Baron Schwartz, and Daniel Nichter

ABOUT PERCONA TOOLKIT

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.

VERSION

pt-heartbeat 2.2.9

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