Re: Communications link failure due to underlying exception...various network exceptions

[John Degner]

I just solved this problem after 4 hours of debugging and fighting configs.

I'm not sure if this will work for everybody, but it was the root of my problem and was definitely a beast to find.

I am running JBoss 4 with MySQL 5.

The problem was that the MySQL wait_timeout setting had been changed. We used to run that setting at 600 (don't ask me why...seems quite large). In JBoss we have files: <MODULE_NAME>-mysql-ds.xml. This file has an entry: <idle-timeout-minutes>. The minimum here is 1 and can only be bumped up in increments of 1 minute (we use a setting of 1 minute). Since our MySQL wait_timeout setting had changed from 600 seconds -> 15 seconds this error was being thrown by JBoss. I can only think that JBoss holds connections and expects them to be active when it does it's checks and if they're not, it calls it a PING TIMEOUT (confusing language >:-| ).

To resolve, check what your application server expects the database timeout to be and try to match them up closely, but err on the side of larger timeouts on the database. I set my app server to 1 minute and MySQL to 75 seconds (to change temporarily in MySQL):
mysql> set global wait_timeout=75;
mysql> select @@global.wait_timeout;

Hope this is the cause for somebody's problem too!