MySQL 9.0 Reference Manual Including MySQL NDB Cluster 9.0
The variables_metadata table
shows, for each server system variable, its name, scope, type,
range of values (where applicable), and description.
The variables_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 the
DOCUMENTATION 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 the
variables_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 the
variables_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 of mysqld
--help
--verbose.
The variables_metadata table has
no indexes.
This table is read-only. The only DML statements allowed are
SELECT and
TABLE; DDL statements including
TRUNCATE TABLE are not
permitted.
The three queries using the
variables_metadata table shown in
the following example provide information about the
binlog_row_image,
innodb_doublewrite_batch_size,
and secure_file_priv system
variables:
mysql>SELECT * FROM variables_metadata WHERE VARIABLE_NAME='binlog_row_image'\G*************************** 1. row *************************** VARIABLE_NAME: binlog_row_image VARIABLE_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 image are logged. 'NOBLOB', means that mysqld avoids logging blob columns whenever possible (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 PK in the table) is logged in the before image, and only changed columns are logged in 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_size VARIABLE_SCOPE: GLOBAL DATA_TYPE: Integer MIN_VALUE: 0 MAX_VALUE: 256 DOCUMENTATION: Number of double write pages to write in a batch 1 row in set (0.00 sec) mysql>SELECT * FROM variables_metadata WHERE VARIABLE_NAME='secure_file_priv'\G*************************** 1. row *************************** VARIABLE_NAME: secure_file_priv VARIABLE_SCOPE: GLOBAL DATA_TYPE: String MIN_VALUE: MAX_VALUE: DOCUMENTATION: Limit LOAD DATA, SELECT ... OUTFILE, and LOAD_FILE() to files within specified directory 1 row in set (0.01 sec)
This table does not show the current values of system
variables; this information is provided by the Performance
Schema global_variables and
session_variables tables.
The variables_metadata table was
added in MySQL 9.0.