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MySQL 8.0 Reference Manual  /  ...  /  Creating a Tablespace Outside of the Data Directory

15.7.5 Creating a Tablespace Outside of the Data Directory

The CREATE TABLE ... DATA DIRECTORY clause permits creating a file-per-table tablespace outside of the data directory. For example, you can use the DATA DIRECTORY clause to create a tablespace on a separate storage device with particular performance or capacity characteristics, such as a fast SSD or a high-capacity HDD.

Be sure of the location that you choose. The DATA DIRECTORY clause cannot be used with ALTER TABLE to change the location later.

The tablespace data file is created in the specified directory, within in a subdirectory named for the schema to which the table belongs.

The following example demonstrates creating a file-per-table tablespace outside of the data directory. It is assumed that the innodb_file_per_table variable is enabled.

mysql> USE test;
Database changed

mysql> CREATE TABLE t1 (c1 INT PRIMARY KEY) DATA DIRECTORY = '/remote/directory';

# MySQL creates the tablespace file in a subdirectory that is named
# for the schema to which the table belongs

shell> cd /remote/directory/test
shell> ls
t1.ibd

When creating a tablespace outside of the data directory, ensure that the directory is known to InnoDB. Otherwise, if the server halts unexpectedly before tablespace data file pages are fully flushed, startup fails when the tablespace is not found during the pre-recovery discovery phase that searches known directories for tablespace data files. To make a directory known, add it to the innodb_directories argument value. innodb_directories is a read-only startup option that defines directories to scan at startup for tablespace data files. Configuring it requires restarting the server.

CREATE TABLE ... TABLESPACE syntax can also be used in combination with the DATA DIRECTORY clause to create a file-per-table tablespace outside of the data directory. To do so, specify innodb_file_per_table as the tablespace name.

mysql> CREATE TABLE t2 (c1 INT PRIMARY KEY) TABLESPACE = innodb_file_per_table
       DATA DIRECTORY = '/remote/directory';

The innodb_file_per_table variable does not need to be enabled when using this method.

Usage Notes:

  • MySQL initially holds the tablespace data file open, preventing you from dismounting the device, but might eventually close the table if the server is busy. Be careful not to accidentally dismount an external device while MySQL is running, or start MySQL while the device is disconnected. Attempting to access a table when the associated tablespace data file is missing causes a serious error that requires a server restart.

    A server restart issues errors and warnings if the tablespace data file is not at the expected path. In this case, you can restore the tablespace data file from a backup or drop the table to remove the information about it from the data dictionary.

  • Before placing a tablespace on an NFS-mounted volume, review potential issues outlined in Using NFS with MySQL.

  • If using an LVM snapshot, file copy, or other file-based mechanism to back up the tablespace data file, always use the FLUSH TABLES ... FOR EXPORT statement first to ensure that all changes buffered in memory are flushed to disk before the backup occurs.

  • Using the DATA DIRECTORY clause is an alternative to using symbolic links, which is not supported.


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