8.12.3.3 Using Symbolic Links for Databases on Windows

On Windows, symbolic links can be used for database directories. This enables you to put a database directory at a different location (for example, on a different disk) by setting up a symbolic link to it. Use of database symlinks on Windows is similar to their use on Unix, although the procedure for setting up the link differs.

Suppose that you want to place the database directory for a database named mydb at D:\data\mydb. To do this, create a symbolic link in the MySQL data directory that points to D:\data\mydb. However, before creating the symbolic link, make sure that the D:\data\mydb directory exists by creating it if necessary. If you already have a database directory named mydb in the data directory, move it to D:\data. Otherwise, the symbolic link is ineffective. To avoid problems, make sure that the server is not running when you move the database directory.

On Windows, you can create a symlink using the mklink command. This command requires administrative privileges.

1. Make sure that the desired path to the database exists. For this example, we use D:\data\mydb, and a database named mydb.

2. If the database does not already exist, issue CREATE DATABASE mydb in the mysql client to create it.

3. Stop the MySQL service.

4. Using Windows Explorer or the command line, move the directory mydb from the data directory to D:\data, replacing the directory of the same name.

5. If you are not already using the command prompt, open it, and change location to the data directory, like this:

   C:\> cd \path\to\datadir

   If your MySQL installation is in the default location, you can use this:

   C:\> cd C:\ProgramData\MySQL\MySQL Server 5.7\Data

6. In the data directory, create a symlink named mydb that points to the location of the database directory:

   C:\> mklink /d mydb D:\data\mydb

7. Start the MySQL service.

After this, all tables created in the database mydb are created in D:\data\mydb.

Alternatively, on any version of Windows supported by MySQL, you can create a symbolic link to a MySQL database by creating a .sym file in the data directory that contains the path to the destination directory. The file should be named db_name.sym, where db_name is the database name.

Support for database symbolic links on Windows using .sym files is enabled by default. If you do not need .sym file symbolic links, you can disable support for them by starting mysqld with the --skip-symbolic-links option. To determine whether your system supports .sym file symbolic links, check the value of the have_symlink system variable using this statement:

SHOW VARIABLES LIKE 'have_symlink';

To create a .sym file symlink, use this procedure:

1. Change location into the data directory:

   C:\> cd \path\to\datadir

2. In the data directory, create a text file named mydb.sym that contains this path name: D:\data\mydb\

   Note

   The path name to the new database and tables should be absolute. If you specify a relative path, the location is relative to the mydb.sym file.

After this, all tables created in the database mydb are created in D:\data\mydb.

Note

Because support for .sym files is redundant with native symlink support available using mklink, use of .sym files is deprecated; expect support for them to be removed in a future MySQL release.

The following limitations apply to the use of .sym files for database symbolic linking on Windows. These limitations do not apply for symlinks created using mklink.

• The symbolic link is not used if a directory with the same name as the database exists in the MySQL data directory.

• The --innodb_file_per_table option cannot be used.

• If you run mysqld as a service, you cannot use a mapped drive to a remote server as the destination of the symbolic link. As a workaround, you can use the full path (\\servername\path\).