MySQL : interactive_timeout v/s wait_timeout

Most of the database intensive applications are worring about the default values of these variables obviously. Developers used to inform me that they need to extend the wait_timeout value in order to complete the query execution.

After some googling, it is found that default “wait_timeout” value is good enough. We may need to reduce it to boost the server performance which will helpful to minimize the “sleep” process loaded in memory. Increasing number of sleeping process will reduces the server performance gradually. So always keep the default value and make it reduce until the program/application does not create any sleeping process which would helpful to improve the performance noticeable. Slow_log_query is another possible reason to have many sleeping process.

interactive_timeout : interactive time out for mysql shell sessions in seconds like mysqldump or mysql command line tools.
wait_timeout” : the amount of seconds during inactivity that MySQL will wait before it will close a connection on a non-interactive connection in seconds.

How to change the these variables

a. changing values at run time 
Log in to the mysql console and set the variable.

mysql> SET  interactive_timeout=200;
Query OK, 0 rows affected (0.01 sec)

mysql> SET GLOBAL  interactive_timeout=200;
Query OK, 0 rows affected (0.00 sec)

mysql> show variables like "%timeout%";
+----------------------------+-------+
| Variable_name              | Value |
+----------------------------+-------+
| connect_timeout            | 200  |
| delayed_insert_timeout     | 300   |
| innodb_lock_wait_timeout   | 50    |
| innodb_rollback_on_timeout | OFF   |
| interactive_timeout        | 200 |
| net_read_timeout           | 200  |
| net_write_timeout          | 200  |
| slave_net_timeout          | 3600  |
| table_lock_wait_timeout    | 50    |
| wait_timeout               | 200 |
+----------------------------+-------+
10 rows in set (0.00 sec)

b. Using my.cnf : Add the following values in /etc/my.cnf” and restart the mysql server.

 [mysqld]
interactive_timeout=180
wait_timeout=180

Pls note that “wait_timeout” would be helpful to clear the sleeping process as “interactive_timeout” does not make any performance improvement since it affect the command line sessions. Obviously increasing the values of connect_timeout, net_read_timeout andnet_write_timeout would help to skip the timeout errors when lengthy queries are being executed.

How to kill the MySQL Sleeping process

mysql> show full processlist;
+-------+------------+---------------------+---------------+---------+------+-------+-----------------------+
| Id    | User       | Host                | db            | Command | Time | State | Info                  |
+-------+------------+---------------------+---------------+---------+------+-------+-----------------------+
|  9435 | user | 192.168.10.15:52180 | db1 | Sleep   |   26 |       | NULL                  |
|  9943 | user | localhost:51179     | db2         | Sleep   |    1 |       | NULL                  |
|  9944 | user | localhost:54007     | db2          | Sleep   |   29 |       | NULL                  |
|  9947 | user | localhost:60638     | db2           | Sleep   |   29 |       | NULL                  |
| 10716 | root       | localhost           | NULL          | Sleep   | 5432 |       | NULL                  |
| 10851 | root       | localhost           | NULL          | Query   |    0 | NULL  | show full processlist |
+-------+------------+---------------------+---------------+---------+------+-------+-----------------------+
6 rows in set (0.00 sec)

mysql> kill 9944;
Query OK, 0 rows affected (0.00 sec)

mysql> show full processlist;
+-------+------------+---------------------+---------------+---------+------+-------+-----------------------+
| Id    | User       | Host                | db            | Command | Time | State | Info                  |
+-------+------------+---------------------+---------------+---------+------+-------+-----------------------+
|  9435 | user | 192.168.10.15:52180 | db1 | Sleep   |    7 |       | NULL                  |
|  9943 | user | localhost:51179     | db2         | Sleep   |    9 |       | NULL                  |
|  9947 | user | localhost:60638     | db2         | Sleep   |   10 |       | NULL                  |
| 10716 | root       | localhost           | NULL          | Sleep   | 5473 |       | NULL                  |
| 10851 | root       | localhost           | NULL          | Query   |    0 | NULL  | show full processlist |
| +-------+------------+---------------------+---------------+---------+------+-------+-----------------------+
7 rows in set (0.01 sec)
mysql>

On thread startup, the session wait_timeout value is initialized from the global wait_timeout value or from the global interactive_timeout value, depending on the type of client (as defined by the CLIENT_INTERACTIVEconnect option to mysql_real_connect()).

参考：

http://www.serveridol.com/2012/04/13/mysql-interactive_timeout-vs-wait_timeout/

http://dev.mysql.com/doc/refman/5.5/en/server-system-variables.html#sysvar_wait_timeout