MySQL 8.4 Reference Manual Including MySQL NDB Cluster 8.4

28.3.15 The INFORMATION_SCHEMA FILES Table

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:

Notes

  • FILES is a nonstandard INFORMATION_SCHEMA table.

  • You must have the PROCESS privilege to query this table.

InnoDB Notes

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

NDB Notes

  • 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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