Internal Details

Internal Details
Every InnoDB per-table tablespace (represented by a *.ibd file) file is labeled with a file format
identifier. The system tablespace (represented by the ibdata files) 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.
Creating a compressed table, or a table with ROW_FORMAT=DYNAMIC, updates the file header for
the corresponding .ibd file and the table type in the InnoDB data dictionary 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 performs a compatibility check when the table is opened. (In many cases, the ALTER TABLE
statement recreates a table and thus changes its properties. The special case of adding or dropping
indexes without rebuilding the table is described in Fast Index Creation in the InnoDB Storage Engine.)
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