MysqlSlaveReplicationLag

MysqlSlaveReplicationLag #

MySQL replication lag on {{ $labels.instance }}

Alert Rule
alert: MysqlSlaveReplicationLag
annotations:
  description: |-
    MySQL replication lag on {{ $labels.instance }}
      VALUE = {{ $value }}
      LABELS = {{ $labels }}    
  runbook: https://srerun.github.io/prometheus-alerts/runbooks/mysqld-exporter/mysqlslavereplicationlag/
  summary: MySQL Slave replication lag (instance {{ $labels.instance }})
expr: ( (mysql_slave_status_seconds_behind_master - mysql_slave_status_sql_delay)
  and ON (instance) mysql_slave_status_master_server_id > 0 ) > 30
for: 1m
labels:
  severity: critical

Here is a runbook for the Prometheus alert rule “MysqlSlaveReplicationLag”:

Meaning #

The “MysqlSlaveReplicationLag” alert is triggered when the replication lag between a MySQL slave and its master exceeds 30 seconds. This means that the slave is not able to keep up with the master’s writes, which can lead to data inconsistencies and other issues.

Impact #

The impact of this alert is high, as it can lead to:

  • Data inconsistencies between the master and slave
  • Slaves becoming out of sync with the master
  • Increased latency for read operations on the slave
  • Potential data loss or corruption

Diagnosis #

To diagnose the issue, follow these steps:

  1. Check the MySQL slave status using the mysql_slave_status metric: mysql_slave_status_seconds_behind_master
  2. Verify the slave’s connection to the master using mysql_slave_status_master_server_id
  3. Check the SQL delay using mysql_slave_status_sql_delay
  4. Review the MySQL error logs for any errors or warnings related to replication
  5. Check the system resources (CPU, memory, disk space) of the slave and master nodes to ensure they are not experiencing any resource constraints

Mitigation #

To mitigate the issue, follow these steps:

  1. Check for any MySQL errors or warnings related to replication and fix them
  2. Verify that the slave is properly configured and connected to the master
  3. Check for any resource constraints on the slave or master nodes and address them
  4. Consider increasing the resources (e.g., CPU, memory) of the slave node to improve its ability to keep up with the master
  5. If the issue persists, consider manually syncing the slave with the master using mysql command-line tools or a third-party replication tool.

Remember to investigate and address the root cause of the replication lag to prevent it from happening again in the future.

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