Starting with version 5.0.21, the built-in InnoDB in MySQL checks the table type before opening a table. Until now, all InnoDB tables have been tagged with the same type, although some changes to the format have been introduced in MySQL versions 4.0, 4.1, and 5.0.

One of the important new features introduced with the InnoDB Plugin is support for identified file formats. This allows the InnoDB Plugin and versions of InnoDB since 5.0.21 to check for file compatibility. It also allows the user to preclude the use of features that would generate downward incompatibilities. By paying attention to the file format used, you can protect your database from corruptions, and ensure a smooth downgrade process.

In general, before using a database file created with the InnoDB Plugin with the built-in InnoDB in MySQL you should verify that the tablespace files (the *.ibd files) are compatible with the built-in InnoDB in MySQL. The InnoDB Plugin can read and write tablespaces in both the formats “Antelope” and “Barracuda”. The built-in InnoDB can only read and write tablespaces in “Antelope” format. To make all tablespaces “legible” to the built-in InnoDB in MySQL, you should follow the instructions in Section 11.3, “How to Downgrade” to reformat all tablespaces to be in the “Antelope” format.

Generally, after a “slow” shutdown of the InnoDB Plugin (innodb_fast_shutdown=0), it should be safe to open the data files with the built-in InnoDB in MySQL. See Section 11.4, “Possible Problems” for a discussion of possible problems that can arise in this scenario and workarounds for them.