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27.12.14.1 Performance Schema persisted_variables Table

The persisted_variables table provides an SQL interface to the mysqld-auto.cnf file that stores persisted global system variable settings, enabling the file contents to be inspected at runtime using SELECT statements. Variables are persisted using SET PERSIST or PERSIST_ONLY statements; see Section 13.7.6.1, “SET Syntax for Variable Assignment”. The table contains a row for each persisted system variable in the file. Variables not persisted do not appear in the table.

The SENSITIVE_VARIABLES_OBSERVER privilege is required to view the values of sensitive system variables in this table.

For information about persisted system variables, see Section 5.1.9.3, “Persisted System Variables”.

Suppose that mysqld-auto.cnf looks like this (slightly reformatted):

{
  "Version": 1,
  "mysql_server": {
    "max_connections": {
      "Value": "1000",
      "Metadata": {
        "Timestamp": 1.519921706e+15,
        "User": "root",
        "Host": "localhost"
      }
    },
    "autocommit": {
      "Value": "ON",
      "Metadata": {
        "Timestamp": 1.519921707e+15,
        "User": "root",
        "Host": "localhost"
      }
    }
  }
}

Then persisted_variables has these contents:

mysql> SELECT * FROM performance_schema.persisted_variables;
+-----------------+----------------+
| VARIABLE_NAME   | VARIABLE_VALUE |
+-----------------+----------------+
| autocommit      | ON             |
| max_connections | 1000           |
+-----------------+----------------+

The persisted_variables table has these columns:

  • VARIABLE_NAME

    The variable name listed in mysqld-auto.cnf.

  • VARIABLE_VALUE

    The value listed for the variable in mysqld-auto.cnf.

persisted_variables has these indexes:

  • Primary key on (VARIABLE_NAME)

TRUNCATE TABLE is not permitted for the persisted_variables table.