On 20/06/2010 00:30, André Warnier wrote: > Robinson, Eric wrote: >> On 17/06/2010 08:59, Robinson, Eric wrote: >>>> If your heap size is right on the edge of your minimum for a Tomcat >>>> instance, you may be doing more GC work than is really needed. >>>> However, if you're satisfied with the response time and CPU >>>> utilization, you should be ok. >> >>> Time to hit the vendor around the head with the cluebat. If the app >>> is happy with less heap space then increasing it is only going to >>> cause problems - mainly that GC when it happens will take longer and >>> trigger longer pauses. You can mitigate this with GC config (later >>> VMs may make the right choices for you anyway) but all this is just >>> adding unecessary complexity. >> >>> Mark >> >> With 160 instances of tomcat on the server, and most of them happy with >> 64-96MB of RAM, could you take an educated guess at the negative impact >> on the server of raising the RAM to 512MB for each instance? How much >> extra CPU utilization do you think I could possibly see from all the >> extra GC? >> > > Just a note here : 160 X 512 MB = 81 GB. > If each Tomcat's JVM is allowed to use up to 512 MB of Heap, there might > be moments where a lot of JVM's will be using close to that amount. > Unless your system can really support that amount of real RAM, you may > be in for massive swapping.
And that could be a major problem. JVMs and swapping do not place nicely together. To quote some folks at work that have been looking at this recently performance "falls of a cliff". Mark --------------------------------------------------------------------- To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
