[Shib-Users] -XX:+UseConcMarkSweepGC

[Russell Beall]

Is there any reason not to try out the garbage collector
UseConcMarkSweepGC instead of UseParallelOldGC?

Thanks,
Russ.

[Taylor Gautier]

I don't recommend it. Every time we have a customer use CMS it always
comes back to bite us.

It seems that CMS slowly fragments the heap meaning at some point it
goes into stop the world GC while it defrags. In high load
environments we see this happen after 5-7 days typically.

When CMS hits this stage you can see pause times as long as 45 minutes
(yes 45 minutes) depending on your heap size.

[Russell Beall]

Thanks for the heads up.

We are soon going to try using the dgc.young you recommended in an
earlier e-mail. Perhaps that will be enough.

I notice that when the Eden space fills up, it collects but spills
some over into the Old collection. If the dgc.young collector can
mark more of these as garbage quicker, perhaps we won't have so much
spillover.

Thanks,
Russ.

[Taylor Gautier]

You can adjust the ratios of the survivor space if you are noticing spill over from Eden that should not make it into the survivor spaces you can change the ratio a bit increasing the size of Eden can help collect more garbage earlier (and is not pauseful).

This setting is briefly discussed in the tuning section of Terracotta: http://www.terracotta.org/web/display/orgsite/Tuning+Terracotta#TuningTerracotta-ExampleGCsettings