MySQL8新特性之全局参数持久化详解

mysql> select * from perfORMance_schema.persisted_variables;
Empty set (0.00 sec)

mysql> show variables like '%max_connections%';
+------------------------+-------+
| Variable_name          | Value |
+------------------------+-------+
| max_connections        | 151   |
| mysqlx_max_connections | 100   |
+------------------------+-------+
2 rows in set (0.00 sec)

mysql> set persist max_connections=300;
Query OK, 0 rows affected (0.00 sec)

mysql> select * from performance_schema.persisted_variables;
+-----------------+----------------+
| VARIABLE_NAME   | VARIABLE_VALUE |
+-----------------+----------------+
| max_connections | 300            |
+-----------------+----------------+
1 row in set (0.00 sec)

{
    "Version": 1, 
    "mysql_server": {
        "max_connections": {
            "Value": "300", 
            "Metadata": {
                "Timestamp": 1632575065787609, 
                "User": "root", 
                "Host": "localhost"
            }
        }
    }
}

mysql> set persist max_connections=DEFAULT;
Query OK, 0 rows affected (0.00 sec)

mysql> select * from performance_schema.persisted_variables;
+-----------------+----------------+
| VARIABLE_NAME   | VARIABLE_VALUE |
+-----------------+----------------+
| max_connections | 151            |
+-----------------+----------------+
1 row in set (0.00 sec)

mysql> RESET PERSIST;
Query OK, 0 rows affected (0.00 sec)

mysql> select * from performance_schema.persisted_variables;
Empty set (0.00 sec)