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26.12.13.1 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 13.7.5.1, “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.

For information about persisted system variables, see Section 13.7.5.1, “SET Syntax for Variable Assignment”.

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           |
+-----------------+----------------+

persisted_variables 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.