Heap Size Variations

[Peng Du]

Hello, guys

I am doing some analysis on the parallel GC for the old generation. But I am
confused by the output of -XX:+PrintGCDetails. I intentionally set the size
of the heap to be [-Xms8m -Xmx8m]. However, the GC log indicated that the
size of heap was varying in between every GC (minor and full).

For example:
===============================================================================================
[GC [PSYoungGen: 768K->128K(896K)] 768K->320K(8064K), 0.0075060 secs]
[Times: user=0.01 sys=0.01, real=0.01 secs]
[GC [PSYoungGen: 876K->128K(896K)] 1069K->406K(8064K), 0.0060870 secs]
[Times: user=0.00 sys=0.00, real=0.00 secs]
[GC [PSYoungGen: 896K->128K(896K)] 1174K->507K(8064K), 0.0058220 secs]
[Times: user=0.01 sys=0.00, real=0.01 secs]
[GC [PSYoungGen: 896K->128K(512K)] 1390K->699K(7680K), 0.0019780 secs]
[Times: user=0.00 sys=0.00, real=0.00 secs]
[GC [PSYoungGen: 512K->64K(704K)] 1083K->727K(7872K), 0.0012320 secs]
[Times: user=0.00 sys=0.00, real=0.00 secs]
[GC [PSYoungGen: 445K->154K(704K)] 1109K->838K(7872K), 0.0017830 secs]
[Times: user=0.00 sys=0.00, real=0.01 secs]
[GC [PSYoungGen: 538K->144K(704K)] 1222K->848K(7872K), 0.0019050 secs]
[Times: user=0.00 sys=0.00, real=0.00 secs]
[GC [PSYoungGen: 416K->32K(704K)] 1262K->882K(7872K), 0.0025930 secs]
[Times: user=0.00 sys=0.00, real=0.00 secs]
[GC [PSYoungGen: 416K->32K(704K)] 1282K->906K(7872K), 0.0025650 secs]
[Times: user=0.00 sys=0.00, real=0.01 secs]
[GC [PSYoungGen: 416K->176K(704K)] 1290K->1058K(7872K), 0.0022590 secs]
[Times: user=0.00 sys=0.00, real=0.00 secs]
[GC [PSYoungGen: 560K->176K(704K)] 1442K->1098K(7872K), 0.0029060 secs]
[Times: user=0.00 sys=0.00, real=0.00 secs]
[GC [PSYoungGen: 560K->64K(704K)] 1482K->1142K(7872K), 0.0014460 secs]
[Times: user=0.00 sys=0.00, real=0.00 secs]
.......................
===============================================================================================

My analysis requires the heap size to be fixed as well as the relative ratio
of each generation within the heap. Is there a way I can strictly restrict
the sizes of the heap and each generation?

Thanks!



Peng Du
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mail.openjdk.java.net/pipermail/hotspot-gc-use/attachments/20090311/2b902f61/attachment.html