Before migrating a MySQL database to AWS Relational Database Service, be sure to understand the impact of that move if any tables in your MySQL database utilize the MyISAM engine. Specifically AWS repeats this warning in many places:
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- This solution is best if you can do it, but there may be reasons you cannot. E.g., vendor vendor support requires that you don't meddle with the database configuration used by their software.
- Understand the impact of making the change. See ; see http://stackoverflow.com/questions/3818759/what-is-innodb-and-myisam-in-mysql.
- If you can swing it, the conversion is easy:
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If you choose to use MyISAM, you can attempt to manually repair tables that become damaged after a crash by using the REPAIR command (see: http://dev.mysql.com/doc/refman/5.5/en/repair-table.html ). However, as noted in the MySQL documentation, there is a good chance that you will not be able to recover all your data.
3. Try to ensure that you get good snapshots.
AWS outlines the following process to endeavour to get good snapshots, if your MySQL RDS DB has MyISAM tables.
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.
- 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;
- Create a snapshot of the RDS instance.
- 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.
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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
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Resources
- Amazon Relational Database Service User Guide. This document has a fair amount to say about MyISAM tables–mostly warnings.
- AWS RDS FAQs. Search for MyISAM on the page)