I have found the same strange behavior - while running parallel gc threads for minor collections reduces the gc pause time, running parallel gc threads for major collections increases the pause time. It makes no sense, but there you have it. You really have to try various heap and gc settings and find the best settings for your app. Have yo considered the CMS collector? With the number of CPUs you have it might be a good option. See this presentation: http://www.cecmg.de/doc/tagung_2007/agenda07/24-mai/2b3-peter-johnson/ind... View the original post : http://www.jboss.org/index.html?module=bb&op=viewtopic&p=4238831#... Reply to the post : http://www.jboss.org/index.html?module=bb&op=posting&mode=reply&a...