在 MySQL 中更改变量 default_password_lifetime 后是否需要运行刷新权限？答案

【问题标题】：Do we need to run flush privileges after changing variable default_password_lifetime in MySQL?在 MySQL 中更改变量 default_password_lifetime 后是否需要运行刷新权限？
【发布时间】：2017-05-17 05:35:06
【问题描述】：

MySQL 在 MySQL-5.7 中有一个新变量，用于保存 mysql 用户的密码到期详细信息 - 特定用户的密码在多少天后到期。

此变量的详细信息：Doc

当我们更改此变量时，是否需要运行刷新权限，否则更改将立即对所有具有默认过期策略的用户生效？

【问题讨论】：

标签： mysql database mysql-5.7

【解决方案1】：

根据文档，应该没有必要：

6.3.6 Password Expiration Policy

...

当客户端成功连接后，服务器会判断是否帐号密码已过期：

服务器检查密码是否已手动过期，如果是，则限制会话。

否则，服务器会根据密码自动过期策略检查密码是否已过期。如果是这样的话，服务器认为密码过期并限制会话。

...

重要提示：更改仅对后续连接生效。

这里是一个例子：

$ mysql
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 13
Server version: 5.7.18

Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> SELECT @@GLOBAL.default_password_lifetime;
+------------------------------------+
| @@GLOBAL.default_password_lifetime |
+------------------------------------+
|                                  0 |
+------------------------------------+
1 row in set (0.00 sec)

mysql> CREATE USER 'johndoe'@'localhost'
    -> IDENTIFIED WITH mysql_native_password AS '*6C8989366EAF75BB670AD8EA7A7FC1176A95CEF4'
    -> PASSWORD EXPIRE DEFAULT;
Query OK, 0 rows affected (0.00 sec)

mysql> exit
Bye

$ mysql -u johndoe -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 14
Server version: 5.7.18

Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> SELECT CURRENT_USER();
+-------------------+
| CURRENT_USER()    |
+-------------------+
| johndoe@localhost |
+-------------------+
1 row in set (0.00 sec)

mysql> exit
Bye

$ mysql
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 15
Server version: 5.7.18

Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> SET @@GLOBAL.default_password_lifetime := 1;
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT @@GLOBAL.default_password_lifetime;
+------------------------------------+
| @@GLOBAL.default_password_lifetime |
+------------------------------------+
|                                  1 |
+------------------------------------+
1 row in set (0.00 sec)

mysql> SELECT NOW();
+---------------------+
| NOW()               |
+---------------------+
| 2010-01-01 00:00:01 |
+---------------------+
1 row in set (0.00 sec)

mysql> \! date -s "2010-01-02 $(date +%H:%M:%S)"
Sat Jan 02 00:00:05 UTC 2010
mysql> SELECT NOW();
+---------------------+
| NOW()               |
+---------------------+
| 2010-01-02 00:00:06 |
+---------------------+
1 row in set (0.01 sec)

mysql> exit
Bye

$ mysql -u johndoe -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 16
Server version: 5.7.18

Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> SELECT CURRENT_USER();
ERROR 1820 (HY000): You must reset your password using ALTER USER statement before executing this statement.

其他感兴趣的信息：

6.2.6 When Privilege Changes Take Effect。

【讨论】：

【解决方案2】：

我认为答案是否定的。

因为default_password_lifetime是一个全局变量，其信息存储在information_schema.GLOBAL_VARAIBLES中，它是一个内存引擎表！

在 mysql 中，flush 操作会导致缓冲区中的数据写回磁盘，只有在 MyISAM 引擎中才有必要；但是，flushprivilege 子句是将有关帐户和权限相关表的数据从磁盘 MyISAM 文件重新加载到内存中。

【讨论】：