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MySQL 8.4 Reference Manual / ... / The INFORMATION_SCHEMA FILES Table

28.3.15 INFORMATION_SCHEMA FILES 表

The FILES table provides information about the files in which MySQL tablespace data is stored.

The FILES table provides information about InnoDB data files. In NDB Cluster, this table also provides information about the files in which NDB Cluster Disk Data tables are stored. For additional information specific to InnoDB, see InnoDB Notes, later in this section; for additional information specific to NDB Cluster, see NDB Notes.

The FILES table has these columns:

FILE_ID

For InnoDB: The tablespace ID, also referred to as the space_id or fil_space_t::id.

For NDB: A file identifier. FILE_ID column values are auto-generated.
FILE_NAME

For InnoDB: The name of the data file. File-per-table and general tablespaces have an .ibd file name extension. Undo tablespaces are prefixed by undo. The system tablespace is prefixed by ibdata. The global temporary tablespace is prefixed by ibtmp. The file name includes the file path, which may be relative to the MySQL data directory (the value of the datadir system variable).

For NDB: 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. In NDB 8.4, the file name is shown with a relative path; for an undo log file, this path is relative to the directory DataDir/ndb_NodeId_fs/LG; for a data file, it is relative to the directory DataDir/ndb_NodeId_fs/TS. This means, for example, that the name of a data file created with ALTER TABLESPACE ts ADD DATAFILE 'data_2.dat' INITIAL SIZE 256M is shown as ./data_2.dat.
FILE_TYPE

For InnoDB: The tablespace file type. There are three possible file types for InnoDB files. TABLESPACE is the file type for any system, general, or file-per-table tablespace file that holds tables, indexes, or other forms of user data. TEMPORARY is the file type for temporary tablespaces. UNDO LOG is the file type for undo tablespaces, which hold undo records.

For NDB: One of the values UNDO LOG or DATAFILE.
TABLESPACE_NAME

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

For InnoDB: General tablespace names are as specified when created. File-per-table tablespace names are shown in the following format: schema_name/table_name. The InnoDB system tablespace name is innodb_system. The global temporary tablespace name is innodb_temporary. Default undo tablespace names are innodb_undo_001 and innodb_undo_002. User-created undo tablespace names are as specified when created.
TABLE_CATALOG

This value is always empty.
TABLE_SCHEMA

This is always NULL.
TABLE_NAME

This is always NULL.
LOGFILE_GROUP_NAME

For InnoDB: This is always NULL.

For NDB: The name of the log file group to which the log file or data file belongs.
LOGFILE_GROUP_NUMBER

For InnoDB: This is always NULL.

For NDB: For a Disk Data undo log file, the auto-generated ID number of the log file group to which the log file belongs. This is the same as the value shown for the id column in the ndbinfo.dict_obj_info table and the log_id column in the ndbinfo.logspaces and ndbinfo.logspaces tables for this undo log file.
ENGINE

For InnoDB: This value is always InnoDB.

For NDB: This value is always ndbcluster.
FULLTEXT_KEYS

This is always NULL.
DELETED_ROWS

This is always NULL.
UPDATE_COUNT

This is always NULL.
FREE_EXTENTS

For InnoDB: The number of fully free extents in the current data file.

For NDB: The number of extents which have not yet been used by the file.
TOTAL_EXTENTS

For InnoDB: The number of full extents used in the current data file. Any partial extent at the end of the file is not counted.

For NDB: The total number of extents allocated to the file.
EXTENT_SIZE

For InnoDB: Extent size is 1048576 (1MB) for files with a 4KB, 8KB, or 16KB page size. Extent size is 2097152 bytes (2MB) for files with a 32KB page size, and 4194304 (4MB) for files with a 64KB page size. FILES does not report InnoDB page size. Page size is defined by the innodb_page_size system variable. Extent size information can also be retrieved from the INNODB_TABLESPACES table where FILES.FILE_ID = INNODB_TABLESPACES.SPACE.

For NDB: The size of an extent for the file in bytes.
INITIAL_SIZE

For InnoDB: The initial size of the file in bytes.

For NDB: 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 InnoDB: The maximum number of bytes permitted in the file. The value is NULL for all data files except for predefined system tablespace data files. Maximum system tablespace file size is defined by innodb_data_file_path. Maximum global temporary tablespace file size is defined by innodb_temp_data_file_path. A NULL value for a predefined system tablespace data file indicates that a file size limit was not defined explicitly.

For NDB: This value is always the same as the INITIAL_SIZE value.
AUTOEXTEND_SIZE

The auto-extend size of the tablespace. For NDB, AUTOEXTEND_SIZE is always NULL.
CREATION_TIME

This is always NULL.
LAST_UPDATE_TIME

This is always NULL.
LAST_ACCESS_TIME

This is always NULL.
RECOVER_TIME

This is always NULL.
TRANSACTION_COUNTER

This is always NULL.
VERSION

For InnoDB: This is always NULL.

For NDB: The version number of the file.
ROW_FORMAT

For InnoDB: This is always NULL.

For NDB: One of FIXED or DYNAMIC.
TABLE_ROWS

This is always NULL.
AVG_ROW_LENGTH

This is always NULL.
DATA_LENGTH

This is always NULL.
MAX_DATA_LENGTH

This is always NULL.
INDEX_LENGTH

This is always NULL.
DATA_FREE

For InnoDB: The total amount of free space (in bytes) for the entire tablespace. Predefined system tablespaces, which include the system tablespace and temporary table tablespaces, may have one or more data files.

For NDB: This is always NULL.
CREATE_TIME

This is always NULL.
UPDATE_TIME

This is always NULL.
CHECK_TIME

This is always NULL.
CHECKSUM

This is always NULL.
STATUS

For InnoDB: This value is NORMAL by default. InnoDB file-per-table tablespaces may report IMPORTING, which indicates that the tablespace is not yet available.

For NDB: For NDB Cluster Disk Data files, this value is always NORMAL.

EXTRA

For InnoDB: This is always NULL.

For NDB: For undo log files, this column shows the undo log buffer size; for data files, it is always NULL. A more detailed explanation is provided in the next few paragraphs.

NDB stores a copy of each data file and each undo log file on each data node in the cluster. The FILES table contains one row for each such file. Suppose that you run the following two statements on an NDB Cluster with four data nodes:

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

CREATE TABLESPACE myts
    ADD DATAFILE 'data_1.dat'
    USE LOGFILE GROUP mygroup
    INITIAL_SIZE 256M
    ENGINE NDBCLUSTER;

After running these two statements 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 ENGINE = 'ndbcluster';

+--------------------+-----------+--------------------------+
| LOGFILE_GROUP_NAME | FILE_TYPE | EXTRA                    |
+--------------------+-----------+--------------------------+
| mygroup            | UNDO LOG  | UNDO_BUFFER_SIZE=8388608 |
| mygroup            | DATAFILE  | NULL                     |
+--------------------+-----------+--------------------------+

FILES is a nonstandard INFORMATION_SCHEMA table.
You must have the PROCESS privilege to query this table.

The following notes apply to InnoDB data files.

Information reported by FILES is obtained from the InnoDB in-memory cache for open files, whereas INNODB_DATAFILES gets its data from the InnoDB SYS_DATAFILES internal data dictionary table.
The information provided by FILES includes global temporary tablespace information which is not available in the InnoDB SYS_DATAFILES internal data dictionary table, and is therefore not included in INNODB_DATAFILES.
Undo tablespace information is shown in FILES when separate undo tablespaces are present, as they are by default in MySQL 8.4.

The following query returns all FILES table information relating to InnoDB tablespaces.

SELECT
  FILE_ID, FILE_NAME, FILE_TYPE, TABLESPACE_NAME, FREE_EXTENTS,
  TOTAL_EXTENTS, EXTENT_SIZE, INITIAL_SIZE, MAXIMUM_SIZE,
  AUTOEXTEND_SIZE, DATA_FREE, STATUS
FROM INFORMATION_SCHEMA.FILES
WHERE ENGINE='InnoDB'\G

The FILES 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.
Much of the information contained in the FILES table can also be found in the ndbinfo files table.
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 NULL.
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 15.1.21, “CREATE TABLESPACE Statement”.
You can obtain information about Disk Data tablespaces using the ndb_desc utility. For more information, see Section 25.6.11.1, “NDB Cluster Disk Data Objects”, as well as the description of ndb_desc.
For additional information, and examples of creating, dropping, and obtaining information about NDB Cluster Disk Data objects, see Section 25.6.11, “NDB Cluster Disk Data Tables”.

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