FILE_ID column values are auto-generated.

FILE_NAME is the name of an UNDO log file created by CREATE LOGFILE GROUP or ALTER LOGFILE GROUP, or of a data file created by CREATE TABLESPACE or ALTER TABLESPACE.

FILE_TYPE is one of the values UNDOFILE or DATAFILE.

TABLESPACE_NAME is the name of the tablespace with which the file is associated.

The value of the TABLESPACE_CATALOG column is always NULL.

TABLE_NAME is the name of the Disk Data table with which the file is associated, if any.

The LOGFILE_GROUP_NAME column gives the name of the log file group to which the log file or data file belongs.

For an UNDO log file, the LOGFILE_GROUP_NUMBER contains the auto-generated ID number of the log file group to which the log file belongs.

For a MySQL Cluster Disk Data log file or data file, the value of the ENGINE column is always NDB or NDBCLUSTER.

For a MySQL Cluster Disk Data log file or data file, the value of the FULLTEXT_KEYS column is always empty.

The FREE EXTENTS column displays the number of extents which have not yet been used by the file. The TOTAL EXTENTS column show the total number of extents allocated to the file.

The difference between these two columns is the number of extents currently in use by the file:

SELECT TOTAL_EXTENTS - FREE_EXTENTS AS extents_used
    FROM INFORMATION_SCHEMA.FILES
    WHERE FILE_NAME = 'myfile.dat';

You can approximate the amount of disk space in use by the file by multiplying this difference by the value of the EXTENT_SIZE column, which gives the size of an extent for the file in bytes:

SELECT (TOTAL_EXTENTS - FREE_EXTENTS) * EXTENT_SIZE AS bytes_used
    FROM INFORMATION_SCHEMA.FILES
    WHERE FILE_NAME = 'myfile.dat';    

Similarly, you can estimate the amount of space that remains available in a given file by multiplying FREE_EXTENTS by EXTENT_SIZE:

SELECT FREE_EXTENTS * EXTENT_SIZE AS bytes_free
    FROM INFORMATION_SCHEMA.FILES
    WHERE FILE_NAME = 'myfile.dat';    

It is also important to remember that once an extent is used, it cannot be freed again without dropping the data file of which it is a part. This means that deletes from a Disk Data table do not release disk space.

The extent size can be set in a CREATE TABLESPACE statement. See Section 12.1.11, “CREATE TABLESPACE Syntax”, for more information.

The INITIAL_SIZE column shows the size in bytes of the file. This is the same value that was used in the INITIAL_SIZE clause of the CREATE LOGFILE GROUP, ALTER LOGFILE GROUP, CREATE TABLESPACE, or ALTER TABLESPACE statement used to create the file.

For MySQL 5.1 Cluster Disk Data files, the value of the MAXIMUM_SIZE column is always the same as INITIAL_SIZE, and the AUTOEXTEND_SIZE column is always empty.

The CREATION_TIME column shows the date and time when the file was created. The LAST_UPDATE_TIME column displays the date and time when the file was last modified. The LAST_ACCESSED column provides the date and time when the file was last accessed by the server.

Currently, the values of these columns are as reported by the operating system, and are not supplied by the NDB storage engine. Where no value is provided by the operating system, these columns display 0000-00-00 00:00:00.

For MySQL Cluster Disk Data files, the value of the RECOVER_TIME and TRANSACTION_COUNTER columns is always 0.

For MySQL 5.1 Cluster Disk Data files, the following columns are always NULL:

For MySQL Cluster Disk Data files, the value of the STATUS column is always NORMAL.

For MySQL Cluster Disk Data files, the EXTRA column shows which data node the file belongs to, as each data node has its own copy of the file. For example, suppose you use this statement on a MySQL Cluster with four data nodes:

CREATE LOGFILE GROUP mygroup
    ADD UNDOFILE 'new_undo.dat'
    INITIAL_SIZE 2G
    ENGINE NDB;

After running the CREATE LOGFILE GROUP statement successfully, you should see a result similar to the one shown here for this query against the FILES table:

mysql> SELECT LOGFILE_GROUP_NAME, FILE_TYPE, EXTRA
    ->     FROM INFORMATION_SCHEMA.FILES
    ->     WHERE FILE_NAME = 'new_undo.dat';
+--------------------+-------------+----------------+
| LOGFILE_GROUP_NAME | FILE_TYPE   | EXTRA          |
+--------------------+-------------+----------------+
| mygroup            | UNDO FILE   | CLUSTER_NODE=3 |
| mygroup            | UNDO FILE   | CLUSTER_NODE=4 |
| mygroup            | UNDO FILE   | CLUSTER_NODE=5 |
| mygroup            | UNDO FILE   | CLUSTER_NODE=6 |
+--------------------+-------------+----------------+
4 rows in set (0.01 sec)

The FILES table is a non-standard table.

An additional row is present in the FILES table following the creation of a logfile group. This row has NULL for the value of the FILE_NAME column. For this row, the value of the FILE_ID column is always 0, that of the FILE_TYPE column is always UNDO FILE, and that of the STATUS column is always NORMAL. In MySQL 6.0 the value of the ENGINE column is always ndbcluster.

This row shows in the FREE_EXTENTS column the total number of free extents available to all undo files belonging to a given log file group whose name and number are shown in the LOGFILE_GROUP_NAME and LOGFILE_GROUP_NUMBER columns, respectively.

Suppose there are no existing log file groups on your MySQL Cluster, and you create one using the following statement:

mysql> CREATE LOGFILE GROUP lg1
    ->   ADD UNDOFILE 'undofile.dat'
    ->   INITIAL_SIZE = 16M
    ->   UNDO_BUFFER_SIZE = 1M
    ->   ENGINE = NDB;
Query OK, 0 rows affected (3.81 sec)

You can now see this NULL row when you query the FILES table:

mysql> SELECT DISTINCT
    ->   FILE_NAME AS File,
    ->   FREE_EXTENTS AS Free,
    ->   TOTAL_EXTENTS AS Total,
    ->   EXTENT_SIZE AS Size,
    ->   INITIAL_SIZE AS Initial
    ->   FROM INFORMATION_SCHEMA.FILES;
+--------------+---------+---------+------+----------+
| File         | Free    | Total   | Size | Initial  |
+--------------+---------+---------+------+----------+
| undofile.dat |    NULL | 4194304 |    4 | 16777216 |
| NULL         | 4184068 |    NULL |    4 |     NULL |
+--------------+---------+---------+------+----------+
2 rows in set (0.01 sec)

The total number of free extents available for undo logging is always somewhat less than the sum of the TOTAL_EXTENTS column values for all undo files in the log file group due to overhead required for maintaining the undo files. This can be seen by adding a second undo file to the log file group, then repeating the previous query against the FILES table:

mysql> ALTER LOGFILE GROUP lg1
    ->   ADD UNDOFILE 'undofile02.dat'
    ->   INITIAL_SIZE = 4M
    ->   ENGINE = NDB;
Query OK, 0 rows affected (1.02 sec)

mysql> SELECT DISTINCT
    ->   FILE_NAME AS File,
    ->   FREE_EXTENTS AS Free,
    ->   TOTAL_EXTENTS AS Total,
    ->   EXTENT_SIZE AS Size,
    ->   INITIAL_SIZE AS Initial
    ->   FROM INFORMATION_SCHEMA.FILES;
+----------------+---------+---------+------+----------+
| File           | Free    | Total   | Size | Initial  |
+----------------+---------+---------+------+----------+
| undofile.dat   |    NULL | 4194304 |    4 | 16777216 |
| undofile02.dat |    NULL | 1048576 |    4 |  4194304 |
| NULL           | 5223944 |    NULL |    4 |     NULL |
+----------------+---------+---------+------+----------+
3 rows in set (0.01 sec)

The amount of free space in bytes which is available for undo logging by Disk Data tables using this log file group can be approximated by multiplying the number of free extents by the initial size:

mysql> SELECT
    ->   FREE_EXTENTS AS 'Free Extents',
    ->   FREE_EXTENTS * EXTENT_SIZE AS 'Free Bytes'
    ->   FROM INFORMATION_SCHEMA.FILES
    ->   WHERE LOGFILE_GROUP_NAME = 'lg1'
    ->   AND FILE_NAME IS NULL;
+--------------+------------+
| Free Extents | Free Bytes |
+--------------+------------+
|      5223944 |   20895776 |
+--------------+------------+
1 row in set (0.02 sec)

If you create a Disk Data table and then insert some rows into it, you can see approximately how much space remains for undo logging afterwards, for example:

mysql> CREATE TABLESPACE ts1
    ->   ADD DATAFILE 'data1.dat'
    ->   USE LOGFILE GROUP lg1
    ->   INITIAL_SIZE 512M
    ->   ENGINE = NDB;
Query OK, 0 rows affected (8.71 sec)

mysql> CREATE TABLE dd (
    ->   c1 INT NOT NULL PRIMARY KEY,
    ->   c2 INT,
    ->   c3 DATE
    ->   )
    ->   TABLESPACE ts1 STORAGE DISK
    ->   ENGINE = NDB;
Query OK, 0 rows affected (2.11 sec)

mysql> INSERT INTO dd VALUES
    ->   (NULL, 1234567890, '2007-02-02'),
    ->   (NULL, 1126789005, '2007-02-03'),
    ->   (NULL, 1357924680, '2007-02-04'),
    ->   (NULL, 1642097531, '2007-02-05');
Query OK, 4 rows affected (0.01 sec)

mysql> SELECT
    ->   FREE_EXTENTS AS 'Free Extents',
    ->   FREE_EXTENTS * EXTENT_SIZE AS 'Free Bytes'
    ->   FROM INFORMATION_SCHEMA.FILES
    ->   WHERE LOGFILE_GROUP_NAME = 'lg1'
    ->   AND FILE_NAME IS NULL;
+--------------+------------+
| Free Extents | Free Bytes |
+--------------+------------+
|      5207565 |   20830260 |
+--------------+------------+
1 row in set (0.01 sec)

There are no SHOW commands associated with the FILES table.

For additional examples using the FILES table to obtain information about Cluster Disk Data tables, see MySQL Cluster Disk Data Tables.