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  1. Stop all activity to your MyISAM tables (that is, close all sessions). You can close all sessions by calling the mysql.rds_kill command for each process that is returned from a MySQL SHOW FULL PROCESSLIST command.

  2. Lock and flush each of your MyISAM tables. For example, the following command locks and flush two tables named myisam_table1 and myisam_table2:
    • FLUSH TABLES myisam_table, myisam_table2 WITH READ LOCK;
  3. Create a snapshot of the RDS instance.
  4. Release the locks on the tables.
    • UNLOCK TABLES;

The lock-and-snap.rb script in https://github.com/CU-CommunityApps/docker-mysql-util attempts to follow this procedure to lock-and-flush MyISAM tables before creating and RDS snapshot.

Warning

We are in the process of understanding this process in greater detail.

Be aware that your database may have MyISAM tables in the internal schemas MySQL uses for operations. Initial trials suggest that flushing-and-locking those tables along with your own tables will block the snapshot from beginning (or at least completing). Snapshot creation times seem nominal if only your own MyISAM tables are flushed-and-locked, leaving out the internal MyISAM tables.

Read Replicas

  • Making snapshots from Read Replicas may also be in the solution mix. However, be aware that creating a new read replica is based on a snapshot, so getting a good snapshot with stable/valid MyISAM table also may be problematic. 
  • RDS documentation warns to be sure to monitor the ReplicaLag metric if you have read replicas setup for MySQL RDS DBs containing MyISAM tables. In particular it warns that if the ReplicaLag metric returns -1, then replication may be having problems because of MyISAM tables.
    • From AWS: "Using a non-transactional storage engine such as MyISAM. Replication is only supported for the InnoDB storage engine."
    • However, AWS might really mean that "Reliable replication is only supported for the InnoDB storage engine." Empirical tests show that data in MyISAM tables is replicated though we haven't tested the reliability of that.

 

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