Analyzing thread stack traces indeed proved useful. Thanks for your help. I looked at http-0.0.0.0-# threads and most of them were in WAIT/BLOCKED state. All these threads seem to be waiting for JDBC connection. Basically it seems that they are waiting on org.jboss.resource.adapter.jdbc.WrapperDataSource.getConnection method. During this I also realized that JBoss XA JDBC pool config is not intelligent (or I might be missing something here). I had specified min-pool-size as 200 and did not specify max-pool-size and it defaulted to 20, which was strange. I am going to post this on JCA forum. Anyways, changing max-pool-size helped a bit and I was able to get another 5% CPU utilized due to that. I also found out that there was a bug report on org.jboss.resource.adapter.jdbc.WrapperDataSource.getConnection being slow. I am not sure if it is fixed in 4.0.5-SP1-ejb3. -Shrinivas View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=3990195#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...