How long is "too long" for MySQL Connections to sleep?
mysqld will timeout database connections based on two server options:


interactive_timeout
wait_timeout


Both are 28,800 seconds (8 hours) by default.

You can set these options in /etc/my.cnf

If your connections are persistent (opened via mysql_pconnect) you could lower these numbers to something reasonable like 600 (10 minutes) or even 60 (1 minute). Or, if your app works just fine, you can leave the default. This is up to you.

You must set these as follows in my.cnf (takes effect after mysqld is restarted):

[mysqld]
interactive_timeout=180
wait_timeout=180


If you do not want to restart mysql, then run these two commands:

SET GLOBAL interactive_timeout = 180;
SET GLOBAL wait_timeout = 180;


This will not close the connections already open. This will cause new connections to close in 180 seconds.