Wednesday, December 21, 2011

innodb file format :antelope and barracuda

The InnoDB Plugin introduces the idea of a named file format and a configuration parameter to enable the use of features that require use of that format. The new file format is the Barracuda format, and the file format supported by prior releases of InnoDB is called file format Antelope. Compressed tables and the new row format that stores long columns off-page require the use of the Barracuda file format or newer. Future versions of InnoDB may introduce a series of file formats, identified with the names of animals, in ascending alphabetical order.

Beginning with this release, every InnoDB per-table tablespace file is labeled with a file format identifier. This does not apply to the system tablespace (the ibdata files) but only the files of separate tablespaces (the *.ibd files where tables and indexes are stored in their own tablespace). As noted below, however, the system tablespace is tagged with the highest file format in use in a group of InnoDB database files, and this tag is checked when the files are opened.

In this release, when you create a compressed table, or a table with ROW_FORMAT=DYNAMIC, the file header for the corresponding .ibd file and the table type in the InnoDB data dictionary are updated with the identifier for the Barracuda file format. From that point forward, the table cannot be used with a version of InnoDB that does not support this new file format. To protect against anomalous behavior, InnoDB version 5.0.21 and later will perform a compatibility check when the table is opened, as described below. (Note that the ALTER TABLE command will, in many cases, cause a table to be recreated and thereby change its properties.

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