问题
I've set a wait_timeout in my.cnf and restarted the server, but the time on idle connections continues to grow larger than the default 100s I set. Any ideas why this is happening?
PS: I'm running ubuntu 12.04 and Mysql Server 5.5. Using Rails 3 with the mysql2 gem.
mysql> SELECT * FROM INFORMATION_SCHEMA.PROCESSLIST ORDER BY TIME DESC LIMIT 20;
+------+------------------+-------------------------------------+--------------------------+---------+------+-------+------+
| ID | USER | HOST | DB | COMMAND | TIME | STATE | INFO |
+------+------------------+-------------------------------------+--------------------------+---------+------+-------+------+
| 760 | user | ip-xxx-xxx-xxx-xxx.ec2.internal:45852 | x | Sleep | 4202 | | NULL |
| 912 | user | ip-xxx-xxx-xxx-xxx.ec2.internal:40929 | y | Sleep | 4194 | | NULL |
| 976 | user | ip-xxx-xxx-xxx-xxx.ec2.internal:40970 | y | Sleep | 4193 | | NULL |
| 836 | user | ip-xxx-xxx-xxx-xxx.ec2.internal:49903 | z | Sleep | 4189 | | NULL |
| 1743 | user | ip-xxx-xxx-xxx-xxx.ec2.internal:44585 | z | Sleep | 4157 | | NULL |
| 1778 | user | ip-xxx-xxx-xxx-xxx.ec2.internal:48714 | a | Sleep | 4154 | | NULL |
回答1:
Turns out the problem is in the mysql2 gem. It does this really awesome thing ...
Essentially it substitutes a default wait_timeout value of about 25 days (2147483s) of its own as the wait_timeout value (probably the session version of wait_timeout) that the connection uses, basically overriding whatever setting we specify on the server.
By setting a wait_timeout: value in config/database.yml the timeout works as it should. When the connection gets killed, however, you get "mysql server has gone away" errors.
By specifying an accompanying reconnect: true option in database.yml, everytime the connection is reused the connection's timer is reset, BUT after that it uses the GLOBAL wait_timeout setting from mysql directly
Hope this helps someone
回答2:
One possibility is that the wait_timeout for a session is being set as the value of the interactive_timeout system variable.
SHOW VARIABLES LIKE 'interactive_timeout'
And the default value for that is 8 hours.
来源：https://stackoverflow.com/questions/23796133/mysql-not-respecting-wait-timeout-setting-in-my-cnf