MySQL 9.3 Reference Manual Including MySQL NDB Cluster 9.3
Symbolic link support as described here, along with the
--symbolic-links option that
controls it, and is deprecated; expect these to be removed
in a future version of MySQL. In addition, the option is
disabled by default.
Symlinks are fully supported only for
MyISAM tables. For files used by tables for
other storage engines, you may get strange problems if you try
to use symbolic links. For InnoDB tables,
use the alternative technique explained in
Section 17.6.1.2, “Creating Tables Externally” instead.
Do not symlink tables on systems that do not have a fully
operational realpath() call. (Linux and
Solaris support realpath()). To determine
whether your system supports symbolic links, check the value
of the have_symlink system
variable using this statement:
SHOW VARIABLES LIKE 'have_symlink';
The handling of symbolic links for MyISAM
tables works as follows:
In the data directory, you always have the data
(.MYD) file and the index
(.MYI) file. The data file and index
file can be moved elsewhere and replaced in the data
directory by symlinks.
You can symlink the data file and the index file independently to different directories.
To instruct a running MySQL server to perform the
symlinking, use the DATA DIRECTORY and
INDEX DIRECTORY options to
CREATE TABLE. See
Section 15.1.22, “CREATE TABLE Statement”. Alternatively, if
mysqld is not running, symlinking can
be accomplished manually using ln -s
from the command line.
The path used with either or both of the DATA
DIRECTORY and INDEX
DIRECTORY options may not include the MySQL
data directory. (Bug #32167)
myisamchk does not replace a symlink
with the data file or index file. It works directly on the
file to which the symlink points. Any temporary files are
created in the directory where the data file or index file
is located. The same is true for the
ALTER TABLE,
OPTIMIZE TABLE, and
REPAIR TABLE statements.
When you drop a table that is using symlinks,
both the symlink and the file to which the
symlink points are dropped. This is an
extremely good reason not to run
mysqld as the root
operating system user or permit operating system users
to have write access to MySQL database directories.
If you rename a table with
ALTER TABLE
... RENAME or RENAME
TABLE and you do not move the table to another
database, the symlinks in the database directory are
renamed to the new names and the data file and index file
are renamed accordingly.
If you use
ALTER TABLE
... RENAME or RENAME
TABLE to move a table to another database, the
table is moved to the other database directory. If the
table name changed, the symlinks in the new database
directory are renamed to the new names and the data file
and index file are renamed accordingly.
If you are not using symlinks, start
mysqld with the
--skip-symbolic-links
option to ensure that no one can use
mysqld to drop or rename a file outside
of the data directory.
These table symlink operations are not supported:
ALTER TABLE ignores the
DATA DIRECTORY and INDEX
DIRECTORY table options.