G1 discovers same garbage again?
java at java4.info
Mon Nov 28 11:18:17 PST 2011
I have a java application with 20gb (large-table) memory and using the
g1 garbage collector.
The application calculates the whole time with 10 threads some ratios
(high cpu load). This is done without producing any garbage. About two
times a minute a request is sent which produce a littlebit garbage.
Since we are working with realtime data we are interested in very short
stop-the-world pauses. Therefore we have used the CMS gc in the past
until we have got problems with fragmentation now.
Therefore I am trying the g1.
This seemed to work very well at first. The stw-pauses were, except the
cleanup pause, very short. This yields me to my first question:
Is this normal and are there any parameters to influence the
cleanup-process? I thought this phase should be short because there is
just finished the counting, the role of the bitmaps is switched and the
next possible garbage regions are detemined. All things, which should be
very fast. So what is taking the time?
The second cause for my email is the crazy behaviour after a few hours:
After the startup of the server it uses about 13.5 gb old-gen memory and
generates very slowly eden-garbage. Since the new allocated memory is
mostly garbage the (young) garbage collections are very fast and g1
decides to grow up the eden space. This works 4 times until eden space
has more than about 3.5 gb memory. After this the gc is making much more
collections and while the collections it discovers new garbage (probably
the old one again). Eden memory usage jumps between 0 and 3.5gb even
though I am sure the java-application is not making more than before. I
assume that it runs during a collection in the old garbage and collects
it again. Is this possible? Or is there an overflow since eden space
uses more than 3.5 gb?
Thanks and regards,
Some useful information:
$ java -version
java version "1.6.0_29"
Java(TM) SE Runtime Environment (build 1.6.0_29-b11)
Java HotSpot(TM) 64-Bit Server VM (build 20.4-b02, mixed mode)
$ cat /proc/meminfo | grep Huge
Hugepagesize: 2048 kB
A few screen-shots of the jconsole memory-view:
The sysout end syserr logfile with the gc logging and PrintFinalFlags:
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