Temp memory needed for CMS heap compaction?

[Kevin McMurtrie]

Does anyone have inside information on how much temporary memory Sun
Java 1.5 needs for heap compaction while using the CMS collector? I'm
tuning new 16GB 64 bit Solaris systems where the Java heap is mostly
small objects. If I shrink the Java heap too much, there's physical
memory sitting idle for all but that one moment in a day when it
compacts. If I make the Java heap too large, it will swap so badly on
compaction that the server will be marked as down. So far I have an
estimate that the temp memory for compaction is 50% of the Java heap
size. Is there a better estimate? I'm not seeing this in Sun's tuning
guides.

 

[Roedy Green]

If I shrink the Java heap too much, there's physical
memory sitting idle for all but that one moment in a day when it
compacts.

There are so many factors, I think the only way to solve this is to do
a binary search to home in on the best value.

See http://mindprod.com/project/tweakable.html

Unfortunately, that best value will change as soon as you process a
bigger data set, or you run something else at the same time.