I am facing an connection pool issue in my clustered JBoss installation. From time to time one of my connection pools will hit the roof and I get a lot of these in my logfile.

 java.sql.SQLException: No ManagedConnections available within configured blocking timeout ( 30000 [ms] ); 

The odd thing is that I can see in the JMX console that the ConnectionCount hit the roof, but at the same time InUseConnectionCount is often quite small. The problem will resolve itself after a couple of minutes but during recovery phase my application will not work (for obvious reasons).

The question is if this indicate an error in the configured timeouts of the connections (I pretty much use defaults), or if my pool is simply too small to handle the peaks. Under normal operation I would say I use ~40% of the configured max number of connections. The reason I just don't increase the max number of connection is that if I actually used up all connections I suspect that InUseConnectionCount would hit the roof. Hence I suspect I might have more issues than just a too small pool size. Maybe InUseConnectionCount has decreased at the time I check jmx-console and it actually do hit the roof? I tend to collect data every second minute.

Any hints are more than welcome.