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MySQL 9.0 Reference Manual

29.12.14.4 Performance Schema variables_metadata Table

Thevariables_metadata table shows, for each server system variable, its name, scope, type, range of values (where applicable), and description.

Thevariables_metadata table contains these columns:

VARIABLE_NAME
The variable name.
VARIABLE_SCOPE
The variable's scope; this is one of the values listed here:
- GLOBAL
  The variable is global-only.
- SESSION
  The variable can have global or session scope.
- SESSION_ONLY
  The variable is session-only.
DATA_TYPE
The variable's type; this is one of the following values:
- Integer
  An integer.
- Numeric
  A decimal value.
- String
  A string.
- Enumeration
  An enumeration.
- Boolean
  A boolean true or false value.
- Set
  A set of values.
Possible values for variables of non-numeric types are often shown in the text of theDOCUMENTATION column; otherwise, see the variable's description in the Manual.
MIN_VALUE
The minimum permitted value for the variable. For a variable that is not numeric, this is always an empty string.
This column is intended to replace thevariables_info table'MAX_VALUE column, which is deprecated in MySQL 9.0.
MAX_VALUE
The maximum permitted value for the variable. For a variable that is not numeric, this is always an empty string.
This column is intended to replace thevariables_info table'MAX_VALUE column, which is deprecated in MySQL 9.0.
DOCUMENTATION
A description of the variable; this is the same text as found in the output ofmysqld--help--verbose.

Thevariables_metadata table has no indexes.

This table is read-only. The only DML statements allowed areSELECT andTABLE; DDL statements includingTRUNCATE TABLE are not permitted.

The three queries using thevariables_metadata table shown in the following example provide information about thebinlog_row_image,innodb_doublewrite_batch_size, andsecure_file_priv system variables:

mysql> SELECT * FROM variables_metadata WHERE VARIABLE_NAME='binlog_row_image'\G*************************** 1. row *************************** VARIABLE_NAME: binlog_row_imageVARIABLE_SCOPE: SESSION     DATA_TYPE: Enumeration     MIN_VALUE:      MAX_VALUE:  DOCUMENTATION: Controls whether rows should be logged in 'FULL', 'NOBLOB' or'MINIMAL' formats. 'FULL', means that all columns in the before and after imageare logged. 'NOBLOB', means that mysqld avoids logging blob columns wheneverpossible (e.g. blob column was not changed or is not part of primary key).'MINIMAL', means that a PK equivalent (PK columns or full row if there is no PKin the table) is logged in the before image, and only changed columns are loggedin the after image. (Default: FULL).      1 row in set (0.01 sec)mysql> SELECT * FROM variables_metadata WHERE VARIABLE_NAME='innodb_doublewrite_batch_size'\G*************************** 1. row *************************** VARIABLE_NAME: innodb_doublewrite_batch_sizeVARIABLE_SCOPE: GLOBAL     DATA_TYPE: Integer     MIN_VALUE: 0     MAX_VALUE: 256 DOCUMENTATION: Number of double write pages to write in a batch1 row in set (0.00 sec)mysql> SELECT * FROM variables_metadata WHERE VARIABLE_NAME='secure_file_priv'\G*************************** 1. row *************************** VARIABLE_NAME: secure_file_privVARIABLE_SCOPE: GLOBAL     DATA_TYPE: String     MIN_VALUE:      MAX_VALUE:  DOCUMENTATION: Limit LOAD DATA, SELECT ... OUTFILE, and LOAD_FILE() to files within specified directory1 row in set (0.01 sec)

This table does not show the current values of system variables; this information is provided by the Performance Schemaglobal_variables andsession_variables tables.

Thevariables_metadata table was added in MySQL 9.0.

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