MySQL 8 新特性之持久化全局變數的修改

在8之前的版本中，對於全局變數的修改，其只會影響其記憶體值，而不會持久化到配置文件中。資料庫重啟，又會恢覆成修改前的值。從8開始，可通過SET PERSIST命令將全局變數的修改持久化到配置文件中。

試舉一例

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=200;
Query OK, 0 rows affected (0.00 sec)

mysql> show variables like '%max_connections%';
+------------------------+-------+
| Variable_name          | Value |
+------------------------+-------+
| max_connections        | 200  |
| mysqlx_max_connections | 100  |
+------------------------+-------+
2 rows in set (0.00 sec)

[root@slowtech ~]# cat /var/lib/mysql/mysqld-auto.cnf 
{ "Version" : 1 , "mysql_server" : { "max_connections" : { "Value" : "200" , "Metadata" : { "Timestamp" : 1525509217566258 , "User" : "root" , "Host" : "localhost" } } } }

mysql> select * from performance_schema.persisted_variables;
+-----------------+----------------+
| VARIABLE_NAME  | VARIABLE_VALUE |
+-----------------+----------------+
| max_connections | 200            |
+-----------------+----------------+
1 row in set (0.00 sec)

mysql> set persist max_connections=default;