MariaDB/pt-heartbeat

pt-heartbeat is a service running on MariaDB servers acting as masters. A process on the source server writes a timestamped row to the heartbeat table every second. A process on a replica compares the most recent entry in the table to the host clock to evaluate the replication lag. MediaWiki load-balancer will avoid replicas that don't have an up-to-date heartbeat entry.

The process writes to a database called heartbeat that contains a table called also heartbeat which has the following structure:

 CREATE TABLE `heartbeat` (
  `ts` varbinary(26) NOT NULL,
  `server_id` int(10) unsigned NOT NULL,
  `file` varbinary(255) DEFAULT NULL,
  `position` bigint(20) unsigned DEFAULT NULL,
  `relay_master_log_file` varbinary(255) DEFAULT NULL,
  `exec_master_log_pos` bigint(20) unsigned DEFAULT NULL,
  `shard` varbinary(10) DEFAULT NULL,
  `datacenter` binary(5) DEFAULT NULL,
  PRIMARY KEY (`server_id`)
 ) ENGINE=InnoDB DEFAULT CHARSET=binary

The process is controlled by pt-heartbeat-wikimedia.service systemctl unit and can be stopped and started as follows:

$ systemctl start pt-heartbeat-wikimedia.service
$ systemctl stop pt-heartbeat-wikimedia.service

The upstream version is developed by Percona, we use a modified version (pt-heartbeat-wikimedia).

See also

• replag.toolforge.org
• [Labs-l] Lag reporting on lab db replicas
• profile/files/wmcs/db/wikireplicas/views/heartbeat-views.sql

This page is a part of the SRE Data Persistence technical documentation
(go here for a list of all our pages)