Question

I am running an application server on Linux 64bit with 8 core CPUs and 6 GB memory.

The server must be highly responsive.

After some inspection I found that the application running on the server creates rather a huge amount of short-lived objects, and has only about 200~400 MB long-lived objects(as long as there is no memory leak)

After reading http://java.sun.com/javase/technologies/hotspot/gc/gc_tuning_6.html
I use these JVM options

-server -Xms2g -Xmx2g -XX:MaxPermSize=256m -XX:NewRatio=1 -XX:+UseConcMarkSweepGC

Result: the minor GC takes 0.01 ~ 0.02 sec, the major GC takes 1 ~ 3 sec
the minor GC happens constantly.

How can I further improve or tune the JVM?

larger heap size? but will it take more time for GC?

larger NewSize and MaxNewSize (for young generation)?

other collector? parallel GC?

is it a good idea to let major GC take place more often? and how?

Answer 1

Result: the minor GC takes 0.01 ~ 0.02 sec, the major GC takes 1 ~ 3 sec the minor GC happens constantly.

Unless you are reporting pauses, I would say that the CMS collector is doing what you have asked it to do. By definition, CMS will use a larger percentage of the CPU than the Serial and Parallel collectors. This is the penalty you pay for low pause times.

If you are seeing 1 to 3 second pause times, I’d say that you need to do some tuning. I’m no expert, but it looks like you should start by reducing the value of CMSInitiatingOccupancyFraction from the default value of 92.

Increasing the heap size will improve the “throughput” of the GC. But if your problem is long pauses, increasing the heap size is likely to make the problem worse.