GC heap sizing and program memory overhead

Question

I'm trying to figure out what's happening with my application.

Problems:

• GC invoking doesn't reduce unused heap size as much as it should, but it should since I'm using serial GC (or UseParNewGC) and agressive heap ratios.

• The program's memory in use is always a lot bigger than the current used and unused heap, too much in my opinion even with other JVM memory included + heap

Command line used:

java -XX:+UseSerialGC -XX:MinHeapFreeRatio=5 -XX:MaxHeapFreeRatio=10 -Xmx2500M -cp XXXXXX.jar xxxx.xxxx.xxxx
pause

tried with UseParNewGC, same results

System: Win7 SP1 4GB RAM + 4GB swapfile 2.99GHZ Java 1.7 + JDK 1.7

Please see picture to make things more clear: https://i.sstatic.net/i3sxw.jpg

Answer 1

Rather than set free ratios, try to set the New Generation to a size that enables the short-lived objects to die. Trying to promote as few as possible to the Old Generation.

Bear in mind that larges Young Generation turns into large collections.

Then set the max Old Generation to a size that does not take too long to full GC but does not constantly runs them.