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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;
Warning

We are in the process of understanding this process in greater detail. Initial trials suggest that this sequence, as recommended by AWS, does not work. We have found that the snapshot will not proceed until the MySQL session holding the locks releases the locks or exits (which releases the locks).

Be aware that your database may have MyISAM tables in the internal schemas MySQL uses for operations. We are not sure what to do with those. It may be the case that trying to flush-and-lock them will block the snapshot from proceeding while flushing-and-locking just your own MyISAM tables will allow snapshotting to proceed as normal.

 

Read Replicas

  • Making Snaps snapshots from Read Replicas may also be in the solution mix. However, be aware the 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.

 

 

Resources

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