4.4. File Format Compatibility

To avoid confusion, for the purposes of this discussion we define the term ib-file set to mean the set of operating system files that InnoDB manages as a unit. The ib-file set includes the following files:

  • The system tablespace (one or more ibdata files) that contain internal system information (including internal catalogs and undo information) and may include user data and indexes.

  • Zero or more single-table tablespaces (also called file per table files, named *.ibd files).

  • (Usually two) InnoDB log files (ib_logfile0 and ib_logfile1), used for crash recovery and in backups.

This collection of files is transactionally consistent, and recoverable as a unit. An ib-file set specifically does not include the related MySQL .frm files that contain metadata about InnoDB tables. The .frm files are created and managed exclusively by MySQL, and can sometimes get out of sync with the internal metadata in InnoDB.

Instead of ib-file set, we might call such a collection a database. However, MySQL uses the word database to mean a logical collection of tables, what other systems term a schema or catalog. Given MySQL terminology, multiple tables (even from more than one database) can be stored in a single ib-file set.

The InnoDB Plugin incorporates several checks to guard against the possible crashes and data corruptions that might occur if you use an ib-file set in a file format that is not supported by the software release in use. These checks take place when the server is started, and when you first access a table. This section describes these checks, how you can control them, and error and warning conditions that may arise.

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