The Replication SQL Thread Stopped alert notifies you when its configured condition is met on MySQL and MariaDB instances so you can investigate and respond.
Mini DBA describes this alert as: A MySQL replica SQL/applier thread is not running. The replica is not applying received changes, so it may be stale even if network IO is healthy. Mini DBA evaluates this alert once a minute so changes are detected quickly.
This alert protects high availability and disaster recovery by warning when replicas, replication slots, or apply processes fall behind. Lag can turn a planned failover into data loss risk or leave reporting users looking at stale data.
Enable it where replication, read replicas, failover, or reporting copies are part of the service design. Disable it on standalone systems that do not use replication so the alert list stays focused.
This alert is based on a state or event rather than a numeric threshold. Tune its schedule, scope, severity, and notification route so that the response matches the importance of the instance.
Check the sender, receiver, apply process, network path, and oldest retained log position. Restart failed replication workers only after capturing the error, then address the root cause such as disk pressure, long transactions, schema drift, network latency, or insufficient replica capacity.
For recovery and replication alerts, route notifications to the people who own recovery objectives. Higher thresholds can be reasonable for reporting replicas, but production failover paths normally need tighter settings and explicit escalation.