java - best way to determine -Xmx and -Xms required for any webapp & standalone app

Question

I'd like to know how to determine the heap size required for a standalone app as well as a webapp running on a tomcat server.

How to determine the same after deployment on the server.

Thanks.

Answer 1

You can start with profiling the memory usage. The JDK (6 upwards) has its Visual VM for example. A tool I personally prefer is the Eclipse Memory Analyzer, originally from SAP, now open. You can analyze heap dumps or hook it up to a java process of your choice.

To programmatically create heap dumps you can use this

Answer 2

Rule suggested by IBM for Sizing the Java heap , it is for IBM SDK but i dont think there would be much difference in these settings for other SDK's.

Size your Java heap so that your application runs with a minimum heap usage of 40%, and a maximum heap usage of 70%.

Answer 3

we use the -Xloggc:gc-log.txtand -XX:+PrintGCdetails option on the VM and let it run for a while (days) with hig Xmx settings and then you can use GCViewer to render a diagram from the log and get an idea of when how much RAM was consumed, i.e. whether there were peaks, limits reached, loads of GCs slowing down the App, etc.