# Monitoring MariaDB read replicas
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For MariaDB read replicas, you can monitor replication lag in Amazon CloudWatch by viewing the Amazon RDS `ReplicaLag` metric. The `ReplicaLag` metric reports the value of the `Seconds_Behind_Master` field of the `SHOW REPLICA STATUS` command. 

**Note**  
Previous versions of MariaDB used `SHOW SLAVE STATUS` instead of `SHOW REPLICA STATUS`. If you are using a MariaDB version before 10.5, then use `SHOW SLAVE STATUS`. 

Common causes for replication lag for MariaDB are the following: 
+ A network outage.
+ Writing to tables with indexes on a read replica. If the `read_only` parameter is not set to 0 on the read replica, it can break replication.
+ Using a nontransactional storage engine such as MyISAM. Replication is only supported for the InnoDB storage engine on MariaDB.

When the `ReplicaLag` metric reaches 0, the replica has caught up to the source DB instance. If the `ReplicaLag` metric returns -1, then replication is currently not active. `ReplicaLag` = -1 is equivalent to `Seconds_Behind_Master` = `NULL`.