原文：http://cenalulu.github.io/mysql/mysql-timeout/
MySQL中有两个关于连接超时的配置项: wait_timeout和interactive_timeout。他们之间在某些条件下会互相继承，那究竟这两个参数会在什么情况下起作用呢？ 本文将会通过一些测试实例来证明总结两者的相互关系。
参数介绍
interactive_timeout
The number of seconds the server waits for activity on an interactive connection before closing it. An interactive client is defined as a client that uses the CLIENT_INTERACTIVE option tomysql_real_connect(). See alsowait_timeout.
wait_timeout
The number of seconds the server waits for activity on a noninteractive connection before closing it. Before MySQL 5.1.41, this timeout applies only to TCP/IP connections, not to connections made through Unix socket files, named pipes, or shared memory.
On thread startup, the session wait_timeout value is initialized from the globalwait_timeout value or from the global interactive_timeout value, depending on the type of client (as defined by the CLIENT_INTERACTIVE connect option tomysql_real_connect()). See also interactive_timeout.
CLIENT_INTERACTIVE
Permit interactive_timeout seconds (instead of wait_timeout seconds) of inactivity before closing the connection. The client’s session wait_timeout variable is set to the value of the session interactive_timeout variable.
简单的说 interactive就是交互式的终端，例如在shell里面直接执行mysql，出现形如mysql>的提示符后就是交互式的连接。而mysql -e ‘select 1’ 这样的直接返回结果的方式就是非交互式的连接。
测试及验证
继承关系
Q：通过socket连接 timeout会从哪个global timeout继承
A：由下例可见，通过socket或者TCP/IP登录，timeout 都继承于global.interactive_timeout;
mysql> set global interactive_timeout = 11111;Query OK, 0 rows affected (0.00 sec)mysql> set global wait_timeout = 22222;Query OK, 0 rows affected (0.00 sec)mysql> show global variables like '%timeout%';+----------------------------+----------+| Variable_name | Value |+----------------------------+----------+| connect_timeout | 10 || delayed_insert_timeout | 300 || innodb_lock_wait_timeout | 50 || innodb_rollback_on_timeout | OFF || interactive_timeout | 11111 || lock_wait_timeout | 31536000 || net_read_timeout | 30 || net_write_timeout | 60 || slave_net_timeout | 3600 || wait_timeout | 22222 |+----------------------------+----------+10 rows in set (0.00 sec)mysql -uroot -ppassword -S /usr/local/mysql3310/mysql.sockWelcome to the MySQL monitor. Commands end with ; or \g.Your MySQL connection id is 4Server version: 5.5.16-log MySQL Community Server (GPL)Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.Oracle is a registered trademark of Oracle Corporation and/or itsaffiliates. Other names may be trademarks of their respectiveowners.Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.mysql> show session variables like '%timeout%';+----------------------------+----------+| Variable_name | Value |+----------------------------+----------+| connect_timeout | 10 || delayed_insert_timeout | 300 || innodb_lock_wait_timeout | 50 || innodb_rollback_on_timeout | OFF || interactive_timeout | 11111 || lock_wait_timeout | 31536000 || net_read_timeout | 30 || net_write_timeout | 60 || slave_net_timeout | 3600 || wait_timeout | 11111 |+----------------------------+----------+10 rows in set (0.00 sec)
Q：通过TCP/IP client 连接， timeout会从哪个global timeout继承
A：由下例可见，通过TCP/IP client 连接后的wait_timeout 仍然继承于global.interactive_timeout
mysql -uroot -ppassword -h 127.0.0.1 --port 3310Welcome to the MySQL monitor. Commands end with ; or \g.Your MySQL connection id is 6Server version: 5.5.16-log MySQL Community Server (GPL)Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.Oracle is a registered trademark of Oracle Corporation and/or itsaffiliates. Other names may be trademarks of their respectiveowners.Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.mysql> show session variables like '%timeout%';+----------------------------+----------+| Variable_name | Value |+----------------------------+----------+| connect_timeout | 10 || delayed_insert_timeout | 300 || innodb_lock_wait_timeout | 50 || innodb_rollback_on_timeout | OFF || interactive_timeout | 11111 || lock_wait_timeout | 31536000 || net_read_timeout | 30 || net_write_timeout | 60 || slave_net_timeout | 3600 || wait_timeout | 11111 |+----------------------------+----------+10 rows in set (0.00 sec)
起效关系
Q：timeout值，对于处于运行状态SQL语句是否起效（即是否等价于执行超时）？
A：由下例可见SQL正在执行状态的等待时间不计入timeout时间。即SQL运行再久也不会因为timeout的配置而中断
mysql> set session wait_timeout=10;Query OK, 0 rows affected (0.00 sec)mysql> set session interactive_timeout=10;Query OK, 0 rows affected (0.00 sec)mysql> select 1,sleep(20) from dual;+---+-----------+| 1 | sleep(20) |+---+-----------+| 1 | 0 |+---+-----------+1 row in set (20.00 sec)mysql> mysql> show session variables like '%timeout%';+----------------------------+----------+| Variable_name | Value |+----------------------------+----------+| connect_timeout | 10 || delayed_insert_timeout | 300 || innodb_lock_wait_timeout | 50 || innodb_rollback_on_timeout | OFF || interactive_timeout | 10 || lock_wait_timeout | 31536000 || net_read_timeout | 30 || net_write_timeout | 60 || slave_net_timeout | 3600 || wait_timeout | 10 |+----------------------------+----------+
Q：同一个session中，wait_timeout 和 interacitve_timeout是否都会生效。
A：只有wait_timeout 会真正起到超时限制的作用
mysql> set session interactive_timeout=10;Query OK, 0 rows affected (0.00 sec)mysql> set session wait_timeout=20;Query OK, 0 rows affected (0.00 sec)mysql> show full processlist;+----+-------------+-----------------+------+---------+--------+-----------------------------------------------------------------------------+-----------------------+-----------+---------------+-----------+| Id | User | Host | db | Command | Time | State | Info | Rows_sent | Rows_examined | Rows_read |+----+-------------+-----------------+------+---------+--------+-----------------------------------------------------------------------------+-----------------------+-----------+---------------+-----------+| 1 | system user | | NULL | Connect | 103749 | Slave has read all relay log; waiting for the slave I/O thread to update it | NULL | 0 | 0 | 1 || 2 | system user | | NULL | Connect | 103750 | Connecting to master | NULL | 0 | 0 | 1 || 3 | root | localhost | NULL | Query | 0 | NULL | show full processlist | 0 | 0 | 11 || 10 | root | localhost:58946 | NULL | Sleep | 20 | | NULL | 0 | 0 | 11 |+----+-------------+-----------------+------+---------+--------+-----------------------------------------------------------------------------+-----------------------+-----------+---------------+-----------+4 rows in set (0.00 sec)mysql> show full processlist;+----+-------------+-----------+------+---------+--------+-----------------------------------------------------------------------------+-----------------------+-----------+---------------+-----------+| Id | User | Host | db | Command | Time | State | Info | Rows_sent | Rows_examined | Rows_read |+----+-------------+-----------+------+---------+--------+-----------------------------------------------------------------------------+-----------------------+-----------+---------------+-----------+| 1 | system user | | NULL | Connect | 103749 | Slave has read all relay log; waiting for the slave I/O thread to update it | NULL | 0 | 0 | 1 || 2 | system user | | NULL | Connect | 103750 | Connecting to master | NULL | 0 | 0 | 1 || 3 | root | localhost | NULL | Query | 0 | NULL | show full processlist | 0 | 0 | 11 |+----+-------------+-----------+------+---------+--------+-----------------------------------------------------------------------------+-----------------------+-----------+---------------+-----------+3 rows in set (0.00 sec)
Q：global timeout和session timeout是否都会作为超时判断依据？
A：只有session级别 timeout 会起作用。即一个session开始后，无论如何修改global级别的timeout都不会影响该session
mysql> set session interactive_timeout = 10;Query OK, 0 rows affected (0.00 sec)mysql> set session wait_timeout = 10;Query OK, 0 rows affected (0.00 sec)mysql> show session variables like '%timeout%';+----------------------------+----------+| Variable_name | Value |+----------------------------+----------+| interactive_timeout | 10 || wait_timeout | 10 |+----------------------------+----------+10 rows in set (0.00 sec)mysql> show global variables like '%timeout%';+----------------------------+----------+| Variable_name | Value |+----------------------------+----------+| interactive_timeout | 20 || wait_timeout | 20 |+----------------------------+----------+10 rows in set (0.00 sec)mysql> show full processlist;+----+-------------+-----------------+------+---------+--------+-----------------------------------------------------------------------------+-----------------------+-----------+---------------+-----------+| Id | User | Host | db | Command | Time | State | Info | Rows_sent | Rows_examined | Rows_read |+----+-------------+-----------------+------+---------+--------+-----------------------------------------------------------------------------+-----------------------+-----------+---------------+-----------+| 3 | root | localhost | NULL | Query | 0 | NULL | show full processlist | 0 | 0 | 11 || 17 | root | localhost:60585 | NULL | Sleep | 10 | | NULL | 10 | 10 | 11 |+----+-------------+-----------------+------+---------+--------+-----------------------------------------------------------------------------+-----------------------+-----------+---------------+-----------+2 rows in set (0.00 sec)mysql> show full processlist;+----+-------------+-----------+------+---------+--------+-----------------------------------------------------------------------------+-----------------------+-----------+---------------+-----------+| Id | User | Host | db | Command | Time | State | Info | Rows_sent | Rows_examined | Rows_read |+----+-------------+-----------+------+---------+--------+-----------------------------------------------------------------------------+-----------------------+-----------+---------------+-----------+| 3 | root | localhost | NULL | Query | 0 | NULL | show full processlist | 0 | 0 | 11 |+----+-------------+-----------+------+---------+--------+-----------------------------------------------------------------------------+-----------------------+-----------+---------------+-----------+1 rows in set (0.00 sec)
mysql> show session variables like '%timeout%';+----------------------------+----------+| Variable_name | Value |+----------------------------+----------+| interactive_timeout | 20 || wait_timeout | 20 |+----------------------------+----------+10 rows in set (0.00 sec)mysql> show global variables like '%timeout%';+----------------------------+----------+| Variable_name | Value |+----------------------------+----------+| interactive_timeout | 10 || wait_timeout | 10 |+----------------------------+----------+10 rows in set (0.00 sec)mysql> show full processlist;+----+-------------+-----------------+------+---------+--------+-----------------------------------------------------------------------------+-----------------------+-----------+---------------+-----------+| Id | User | Host | db | Command | Time | State | Info | Rows_sent | Rows_examined | Rows_read |+----+-------------+-----------------+------+---------+--------+-----------------------------------------------------------------------------+-----------------------+-----------+---------------+-----------+| 3 | root | localhost | NULL | Query | 0 | NULL | show full processlist | 0 | 0 | 11 || 19 | root | localhost:50276 | NULL | Sleep | 19 | | NULL | 10 | 10 | 11 |+----+-------------+-----------------+------+---------+--------+-----------------------------------------------------------------------------+-----------------------+-----------+---------------+-----------+2 rows in set (0.00 sec)mysql> show full processlist;+----+-------------+-----------+------+---------+--------+-----------------------------------------------------------------------------+-----------------------+-----------+---------------+-----------+| Id | User | Host | db | Command | Time | State | Info | Rows_sent | Rows_examined | Rows_read |+----+-------------+-----------+------+---------+--------+-----------------------------------------------------------------------------+-----------------------+-----------+---------------+-----------+| 3 | root | localhost | NULL | Query | 0 | NULL | show full processlist | 0 | 0 | 11 |+----+-------------+-----------+------+---------+--------+-----------------------------------------------------------------------------+-----------------------+-----------+---------------+-----------+1 rows in set (0.00 sec)
总结
由以上的阶段测试可以获得以下结论。
- 超时时间只对非活动状态的connection进行计算。
- 超时时间只以session级别的
wait_timeout 为超时依据，global级别只决定session初始化时的超时默认值。 - 交互式连接的
wait_timeout 继承于global的interactive_timeout。非交互式连接的wait_timeout继承于global的wait_timeout - 继承关系和超时对 TCP/IP 和 Socket 连接均有效果
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