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MySQL 5.6 Reference Manual / ... / The INFORMATION_SCHEMA FILES Table

21.5.1 The INFORMATION_SCHEMA FILES Table

The FILES table provides information about the files in which MySQL NDB Disk Data tables are stored.

The FILES table has these columns:

FILE_ID
A file identifier. FILE_ID column values are auto-generated.
FILE_NAME
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
One of the values UNDO LOG, DATAFILE, or TABLESPACE.
TABLESPACE_NAME
The name of the tablespace with which the file is associated.
TABLE_CATALOG
This value is always empty.
TABLE_SCHEMA
This value is always NULL.
TABLE_NAME
The name of the Disk Data table with which the file is associated, if any.
LOGFILE_GROUP_NAME
The name of the log file group to which the log file or data file belongs.
LOGFILE_GROUP_NUMBER
For an UNDO log file, the auto-generated ID number of the log file group to which the log file belongs.
ENGINE
For an NDB Cluster Disk Data log file or data file, this value always NDB or NDBCLUSTER.
FULLTEXT_KEYS
For an NDB Cluster Disk Data log file or data file, this value is always empty.
DELETED_ROWS
This value is always NULL.
UPDATE_COUNT
This value is always NULL.
FREE_EXTENTS
The number of extents which have not yet been used by the file.
TOTAL_EXTENTS
The total number of extents allocated to the file.
EXTENT_SIZE
The size of an extent for the file in bytes.
INITIAL_SIZE
The size of the file in bytes. 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.
MAXIMUM_SIZE
For NDB Cluster Disk Data files, this value is always the same as the INITIAL_SIZE value.
AUTOEXTEND_SIZE
For NDB Cluster Disk Data files, this value is always empty.
CREATION_TIME
The date and time when the file was created.
LAST_UPDATE_TIME
The date and time when the file was last modified.
LAST_ACCESS_TIME
The date and time when the file was last accessed by the server.
RECOVER_TIME
For NDB Cluster Disk Data files, this value is always 0.
TRANSACTION_COUNTER
For NDB Cluster Disk Data files, this value is always 0.
VERSION
For NDB Cluster Disk Data files, this value is always NULL.
ROW_FORMAT
For NDB Cluster Disk Data files, this value is always NULL.
TABLE_ROWS
For NDB Cluster Disk Data files, this value is always NULL.
AVG_ROW_LENGTH
For NDB Cluster Disk Data files, this value is always NULL.
DATA_LENGTH
For NDB Cluster Disk Data files, this value is always NULL.
MAX_DATA_LENGTH
For NDB Cluster Disk Data files, this value is always NULL.
INDEX_LENGTH
For NDB Cluster Disk Data files, this value is always NULL.
DATA_FREE
For NDB Cluster Disk Data files, this value is always NULL.
CREATE_TIME
For NDB Cluster Disk Data files, this value is always NULL.
UPDATE_TIME
For NDB Cluster Disk Data files, this value is always NULL.
CHECK_TIME
For NDB Cluster Disk Data files, this value is always NULL.
CHECKSUM
For NDB Cluster Disk Data files, this value is always NULL.
STATUS
For NDB Cluster Disk Data files, this value is always NORMAL.

EXTRA

For NDB Cluster Disk Data files, the EXTRA column shows which data node the file belongs to (each data node having its own copy), as well as the size of its undo buffer. Suppose that you use this statement on an NDB 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 LOG  | CLUSTER_NODE=5;UNDO_BUFFER_SIZE=8388608 |
| mygroup            | UNDO LOG  | CLUSTER_NODE=6;UNDO_BUFFER_SIZE=8388608 |
| mygroup            | UNDO LOG  | CLUSTER_NODE=7;UNDO_BUFFER_SIZE=8388608 |
| mygroup            | UNDO LOG  | CLUSTER_NODE=8;UNDO_BUFFER_SIZE=8388608 |
+--------------------+-----------+-----------------------------------------+

Notes

The FILES table is a nonstandard INFORMATION_SCHEMA table.

NDB Notes

This table provides information about Disk Data files only; you cannot use it for determining disk space allocation or availability for individual NDB tables. However, it is possible to see how much space is allocated for each NDB table having data stored on disk—as well as how much remains available for storage of data on disk for that table—using ndb_desc. For more information, see Section 18.5.10, “ndb_desc — Describe NDB Tables”.
The CREATION_TIME, LAST_UPDATE_TIME, and LAST_ACCESSED values 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.
The difference between the TOTAL EXTENTS and FREE_EXTENTS 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';
```
To approximate the amount of disk space in use by the file, multiply that 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';
```
Important

The byte values produced by the preceding queries are approximations only, and their precision is inversely proportional to the value of EXTENT_SIZE. That is, the larger EXTENT_SIZE becomes, the less accurate the approximations are.

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. For more information, see Section 13.1.18, “CREATE TABLESPACE Statement”.

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 LOG, and that of the STATUS column is always NORMAL. The value of the ENGINE column is always NDBCLUSTER.

The FREE_EXTENTS column in this row shows 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 NDB 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;

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 |
+--------------+---------+---------+------+----------+

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;

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 |
+----------------+---------+---------+------+----------+

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 |
+--------------+------------+

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

mysql> CREATE TABLESPACE ts1
         ADD DATAFILE 'data1.dat'
         USE LOGFILE GROUP lg1
         INITIAL_SIZE 512M
         ENGINE = NDB;

mysql> CREATE TABLE dd (
         c1 INT NOT NULL PRIMARY KEY,
         c2 INT,
         c3 DATE
         )
         TABLESPACE ts1 STORAGE DISK
         ENGINE = NDB;

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');

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 |
+--------------+------------+

An additional row is present in the FILES table for any NDB Cluster tablespace, whether or not any data files are associated with the tablespace. 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 TABLESPACE, and that of the STATUS column is always NORMAL. The value of the ENGINE column is always NDBCLUSTER.
For additional information, and examples of creating and dropping NDB Cluster Disk Data objects, see Section 18.6.11, “NDB Cluster Disk Data Tables”.

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