# 清除所有的已持久化的变量
mysql> reset persist ;
Query OK, 0 rows affected (0.00 sec)
mysql> select * from performance_schema.persisted_variables ;
Empty set (0.00 sec)
mysql> set session net_read_timeout=20;
Query OK, 0 rows affected (0.00 sec)
mysql> select @@global.net_read_timeout,@@session.net_read_timeout ;
+---------------------------+----------------------------+
| @@global.net_read_timeout | @@session.net_read_timeout |
+---------------------------+----------------------------+
| 30 | 20 |
+---------------------------+----------------------------+
1 row in set (0.00 sec)