InnoDB in MySQL 5.5 contains several important new features:

Upward and Downward Compatibility

Note that the ability to use data compression and the new row format require the use of a new InnoDB file format called Barracuda. The previous file format, used by the built-in InnoDB in MySQL 5.1 and earlier, is now called Antelope and does not support these features, but does support the other features introduced with the InnoDB storage engine.

The InnoDB storage engine is upward compatible from standard InnoDB as built in to, and distributed with, MySQL. Existing databases can be used with the InnoDB Storage Engine for MySQL. The new parameter innodb_file_format can help protect upward and downward compatibility between InnoDB versions and database files, allowing users to enable or disable use of new features that can only be used with certain versions of InnoDB.

InnoDB since version 5.0.21 has a safety feature that prevents it from opening tables that are in an unknown format. However, the system tablespace may contain references to new-format tables that confuse the built-in InnoDB in MySQL 5.1 and earlier. These references are cleared in a slow shutdown.

With previous versions of InnoDB, no error would be returned until you try to access a table that is in a format “too new” for the software. To provide early feedback, InnoDB 1.1 checks the system tablespace before startup to ensure that the file format used in the database is supported by the storage engine. See Section 4.2.1, “Compatibility Check When InnoDB Is Started” for the details.