MysqlSlaveIoThreadNotRunning

MysqlSlaveIoThreadNotRunning #

MySQL Slave IO thread not running on {{ $labels.instance }}

Alert Rule
alert: MysqlSlaveIoThreadNotRunning
annotations:
  description: |-
    MySQL Slave IO thread not running on {{ $labels.instance }}
      VALUE = {{ $value }}
      LABELS = {{ $labels }}    
  runbook: https://srerun.github.io/prometheus-alerts/runbooks/mysqld-exporter/mysqlslaveiothreadnotrunning/
  summary: MySQL Slave IO thread not running (instance {{ $labels.instance }})
expr: ( mysql_slave_status_slave_io_running and ON (instance) mysql_slave_status_master_server_id
  > 0 ) == 0
for: 0m
labels:
  severity: critical

Here is a sample runbook for the MysqlSlaveIoThreadNotRunning alert:

Meaning #

The MysqlSlaveIoThreadNotRunning alert indicates that the MySQL slave instance’s IO thread is not running, which is a critical component for replication. This thread is responsible for reading events from the master and applying them to the slave. If the IO thread is not running, the slave will fall behind the master, leading to inconsistencies and potential data loss.

Impact #

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

  • Inconsistencies between the master and slave databases
  • Data loss or corruption
  • Downtime or unavailability of the slave instance
  • Potential cascading failures in dependent systems

Diagnosis #

To diagnose the issue, follow these steps:

  1. Check the MySQL error logs for any errors or warnings related to the IO thread.
  2. Verify the MySQL slave status using the SHOW SLAVE STATUS command.
  3. Check the mysql_slave_status_slave_io_running metric in Prometheus to confirm that the IO thread is indeed not running.
  4. Investigate the system logs for any underlying issues, such as disk space issues, network connectivity problems, or resource constraints.

Mitigation #

To mitigate the issue, follow these steps:

  1. Restart the MySQL slave instance to attempt to restart the IO thread.
  2. Check the MySQL configuration file to ensure that the IO thread is enabled and configured correctly.
  3. Verify that the master and slave instances are properly configured and that the replication is set up correctly.
  4. Perform a manual sync of the slave instance with the master instance to ensure data consistency.
  5. If the issue persists, consider escalating to a senior engineer or DBA for further assistance.
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