MySQL 8.0 Reference Manual Including MySQL NDB Cluster 8.0

15.6.3.2 File-Per-Table Tablespaces

Historically, InnoDB tables were stored in the system tablespace. This monolithic approach was targeted at machines dedicated to database processing, with carefully planned data growth, where any disk storage allocated to MySQL would never be needed for other purposes. The file-per-table tablespace feature provides a more flexible alternative, where each InnoDB table is stored in its own tablespace data file (.ibd file). This feature is controlled by the innodb_file_per_table configuration option, which is enabled by default.

Advantages
Potential Disadvantages
Enabling File-Per-Table Tablespaces

The innodb_file_per_table option is enabled by default.

To set the innodb_file_per_table option at startup, start the server with the --innodb_file_per_table command-line option, or add this line to the [mysqld] section of my.cnf:

[mysqld]
innodb_file_per_table=1

You can also set innodb_file_per_table dynamically, while the server is running:

mysql> SET GLOBAL innodb_file_per_table=1;

With innodb_file_per_table enabled, you can store InnoDB tables in a tbl_name.ibd file. Unlike the MyISAM storage engine, with its separate tbl_name.MYD and tbl_name.MYI files for indexes and data, InnoDB stores the data and the indexes together in a single .ibd file.

If you disable innodb_file_per_table in your startup options and restart the server, or disable it with the SET GLOBAL command, InnoDB creates new tables inside the system tablespace unless you have explicitly placed the table in file-per-table tablespace or general tablespace using the CREATE TABLE ... TABLESPACE option.

You can always read and write any InnoDB tables, regardless of the file-per-table setting.

To move a table from the system tablespace to its own tablespace, change the innodb_file_per_table setting and rebuild the table:

mysql> SET GLOBAL innodb_file_per_table=1;
mysql> ALTER TABLE table_name ENGINE=InnoDB;

Tables added to the system tablespace using CREATE TABLE ... TABLESPACE or ALTER TABLE ... TABLESPACE syntax are not affected by the innodb_file_per_table setting. To move these tables from the system tablespace to a file-per-table tablespace, they must be moved explicitly using ALTER TABLE ... TABLESPACE syntax.

Note

InnoDB always needs the system tablespace because it puts its internal data dictionary and undo logs there. The .ibd files are not sufficient for InnoDB to operate.

When a table is moved out of the system tablespace into its own .ibd file, the data files that make up the system tablespace remain the same size. The space formerly occupied by the table can be reused for new InnoDB data, but is not reclaimed for use by the operating system. When moving large InnoDB tables out of the system tablespace, where disk space is limited, you may prefer to enable innodb_file_per_table and recreate the entire instance using the mysqldump command. As mentioned above, tables added to the system tablespace using CREATE TABLE ... TABLESPACE or ALTER TABLE ... TABLESPACE syntax are not affected by the innodb_file_per_table setting. These tables must be moved individually.