Compressed tables are stored in a format that previous versions of InnoDB cannot process. To preserve downward compatibility of database files, compression can be specified only when the “Barracuda” data file format is enabled using the configuration parameter innodb_file_format.

Table compression is also not available for the InnoDB system tablespace. The system tablespace (space 0, the ibdata* files) may contain user data, but it also contains internal InnoDB system information, and therefore is never compressed. Thus, compression applies only to tables (and indexes) stored in their own tablespaces.

To use compression, enable the “file per table” mode using the configuration parameter innodb_file_per_table and enable the “Barracuda” disk file format using the parameter innodb_file_format. You can set these parameters in the MySQL option file my.cnf or my.ini, but both are dynamic parameters that you can change with the SET command without shutting down the MySQL server.

Specifying ROW_FORMAT=COMPRESSED or a KEY_BLOCK_SIZE in the CREATE TABLE or ALTER TABLE commands if the “Barracuda” file format has not been enabled produces these warnings that you can view with the SHOW WARNINGS command:

The “non-strict” behavior is intended to permit you to import a mysqldump file into a database that does not support compressed tables, even if the source database contained compressed tables. In that case, the InnoDB storage engine creates the table in ROW_FORMAT=COMPACT instead of preventing the operation.

When you import the dump file into a new database, if you want to have the tables re-created as they exist in the original database, ensure the server is running the InnoDB storage engine with the proper settings for the configuration parameters innodb_file_format and innodb_file_per_table,