JVM size for Websphere 7.0

Hi I was told by Oracle/IBM that with 64 bit OS, there is no limitation on the JVM size for web sphere application. Has any one tried to use more than 1.2GB. Any risks?. What is the JVM size you are currently using in Prod. We are on 9.1 ( TR 9.1.0.4) on windows platform

Heard the same thing. Haven't tried it on WAS, but I can tell you that with WebLogic, we saw much greater stability and performance putting the JVM's at 4GB each, whereas initially we had them set to the old recommendations.

Hi

Thanks for the confirmation. I am going to try it in my test environment with 4 GB. I am actually thinking of going about 14 GB in Production as I have 32 GB on that machine. Planning to have two JVM each with 14 GB and 4 GB allocated for OS

If you have an high heap size the jvm will spend more time in garbage collection. So you need to balance the heap size and the application response time. If you are on WebSphere you have the cluster option without additional cost. So you can split you architecture in a horizontal cluster (for example 6 profiles with 4GB of heap size). Take care about CPU usage too. The JVM architecture span native thread that are splitted to separate core (when available). I tend to be pessimistic in JVM sizing for JD Edwards clients running many custom applications, so 1 jvm with 4GB heap and 2 core for 25 users.

Thanks Bruno, We do have WebSphere clustering. With two JVM. Garbage collection was certainly one of my concerns. If that an issue, I can try to create more JVM's with 4 GB Each.

Yes, may be an issue but there are others advantage too running more jvm with smallest heap size. First of all if some applications consume a lot of memory you will never find it if you have a big jvm (or it will be more difficult to isolate the problem). Running multiple jvm will isolate the failure; if one jvm goes down only a few users will be affected. If you don't have any hardware constraint I suggest to go with additional clustered resources.