When a table is first accessed, InnoDB (including some releases prior to InnoDB 1.0) checks that the file format of the tablespace in which the table is stored is fully supported. This check prevents crashes or corruptions that would otherwise occur when tables using a “too new” data structure are encountered.
All tables using any file format supported by a release can be
read or written (assuming the user has sufficient privileges).
The setting of the system configuration parameter
innodb_file_format can prevent
creating a new table that uses a specific file format, even if
the fole format is supported by a given release. Such a setting
might be used to preserve backward compatibility, but it does
not prevent accessing any table that uses a supported format.
Versions of MySQL older than 5.0.21 cannot reliably use database files created by newer versions if a new file format was used when a table was created. To prevent various error conditions or corruptions, InnoDB checks file format compatibility when it opens a file (for example, upon first access to a table). If the currently running version of InnoDB does not support the file format identified by the table type in the InnoDB data dictionary, MySQL reports the following error:
ERROR 1146 (42S02): Table '
t1' doesn't exist
InnoDB also writes a message to the error log:
t1: unknown table type
The table type should be equal to the tablespace flags, which contains the file format version as discussed in Section 14.11.3, “Identifying the File Format in Use”.
Versions of InnoDB prior to MySQL 4.1 did not include table format identifiers in the database files, and versions prior to MySQL 5.0.21 did not include a table format compatibility check. Therefore, there is no way to ensure proper operations if a table in a newer file format is used with versions of InnoDB prior to 5.0.21.
The file format management capability in InnoDB 1.0 and higher (tablespace tagging and run-time checks) allows InnoDB to verify as soon as possible that the running version of software can properly process the tables existing in the database.
If you permit InnoDB to open a database containing files in a
format it does not support (by setting the parameter
OFF), the table-level checking described in
this section still applies.
Users are strongly urged not to use database files that contain Barracuda file format tables with releases of InnoDB older than the MySQL 5.1 with the InnoDB Plugin. It is possible to “downgrade” such tables to the Antelope format with the procedure described in Section 14.11.4, “Downgrading the File Format”.