JVM performance tuning for large applications

Question

The default JVM parameters are not optimal for running large applications. Any insights from people who have tuned it on a real application would be helpful. We are running the application on a 32-bit windows machine, where the client JVM is used by default. We have added -server and changed the NewRatio to 1:3 (A larger young generation).

Any other parameters/tuning which you have tried and found useful?

[Update] The specific type of application I'm talking about is a server application that are rarely shutdown, taking at least -Xmx1024m. Also assume that the application is profiled already. I'm looking for general guidelines in terms of JVM performance only.

Answer 1

There are great quantities of that information around.

First, profile the code before tuning the JVM.

Second, read the JVM documentation carefully; there are a lot of sort of "urban legends" around. For exaple, the -server flag only helps if the JVM is staying resident and running for some time; -server "turns up" the JIT/HotSpot, and that needs to have many passes through the same path to get turned up. -server, on the other hand, slows initial execution of the JVM, as there's more setup time.

There are several good books and websites around. See, for example, http://www.javaperformancetuning.com/

Answer 2

This will be highly dependent on your application and the vendor and version of the JVM. You need to be clear about what you consider to be a performance problem. Are you concerned with certain critical sections of code? Have you profiled the app yet? Is the JVM spending too much time garbage collecting?

I would probably start with the -verbose:gc JVM option to watch how garbage collecting is working. Many times, the simplest fix to just increase the max heap size with -Xmx . If you learn to interpret the -verbose:gc output, it will tell you nearly all you need to know about tuning the JVM as a whole. But doing this alone will not magically make badly tuned code just go faster. Most of the JVM tuning options are designed to improve the performance of the garbage collector and/or memory sizes.

For profiling, I like yourkit.com

Answer 3

Look here (or do a google search for hotspot tuning) http://java.sun.com/javase/technologies/hotspot/gc/gc_tuning_6.html

You definitely want to profile your app before you try to tune the vm. NetBeans has a nice profiler built into it that will let you see all sorts of things.

I once had someone tell me that the GC was broken for their app - I looked at the code and found that they never closed any of their database query results so they were retaining massive amounts of byte arrays. Once we closed the results the time went from over 20 mins and a GB of memory to about 2 mins and a very small amount of memory. They were able to remove the JVM tuning parameters and things were happy.

Answer 4

The absolute best way to answer this is to perform controlled testing on the application in as close to a 'production' environment as you can create. It's quite possible that the use of -server, a reasonable starting heap size and the relatively smart behavior of recent JVMs will behave as well or better than the vast majority of settings one would normally try.

There is one specific exception to this broad generalization: in the case that you are running in a web container, there is a really high chance that you will want to increase the permanent generation settings.

Answer 5

I suggest you profile your application with CPU sampling and object allocation monitoring turned on at the same time. You will find you get very different results which can be helpful in tuning your code. Also try using the built in hprof profiler, it can give very different results as well.

In general profiling your application makes much more difference than JVM args.

Answer 6

hi guys.

you may be interested in reading this. good example of tuning applications using different JVMs.

http://bigdatamatters.com/bigdatamatters/2009/08/jvm-performance.html