CMS very long pauses
We are using JRE1.4._10 on Windows with large heaps
min=max=1400M
We are also using CMS in order to reduce pauses.
Two problems are experienced:
On startup we see a GC pause which takes more than an hour (it happens in one every four restarts)
On heavy load from time to time there are 2-3 minutes application pauses.
The memory is not depleted we have at least 200M free memory
(Young generation is 80MB)
Any ideas why it happen and how can it be solved.
[512 byte] By [
haimya] at [2007-10-3 11:45:16]
> We are using JRE1.4._10 on Windows with large heaps
> min=max=1400M
> We are also using CMS in order to reduce pauses.
> (Young generation is 80MB)
So, you're running with something like-server -XX:+UseConcMarkSweepGC -XX:+UseParNewGC -Xms1400m -Xmx1400m -Xmn80m
> On startup we see a GC pause which takes more than an
> hour (it happens in one every four restarts)
This makes no sense at all.
How can there be anything to GC when the JVM is only just starting up?
> On heavy load from time to time there are 2-3 minutes
> application pauses.
http://java.sun.com/performance/reference/whitepapers/tuning.html#section4.2.6
http://blogs.sun.com/jonthecollector/entry/what_the_heck_s_a
How much physical memory do you have on your machine? If you reboot your machine
and then start up the application, do you ever see the 1 hour long pause? Can you
post some of the output with -XX:+PrintGCDetails turned on? Is there anything
else running on the machine or is it just this application?
Some more info
1. We have 4GB of physical memory. (Windows 2003 enterprise edition2 with to xeon cpus)
2. I am familiar with these articles and I know that we should expect Full/Stop the world GC from time to time
I do not understand why does it take so much time to finish, When not using CMS GC takes at most 20 seconds. If CMS fails I would expect same time.
3. We are loading a big cache and performing a lot of computation at startup so maybe this is why it can happen/
4.When not using CMS we do not experience the 1hour freeze at startup
5. When using -XX:+CMSParallelRemarkEnabled we do not see the freeze anymore but the server crashes from time to time.
haimya at 2007-7-15 14:17:35 >
There have been a lot of fixes/bugs with too long taking GCs. Furthermore stability of all the paralell collectors was wastly improved in java-5/6.
Are you using large reference-arrays (e.g. String[]) - there have been also bug-fixes and it would explain your problem.
1.) Java-1.4 is really old, because java-6 was just released and is mostly backward compatible I would recommend to give it a try.
You'll definitifly see much better stability (because some long-standing implementation problems have been fixed) and higher performance (in the range of 10-20% on our servers). We've not seen any incompatibility when migrating from 1.4.2 to 5.0 and just recently to 6.0. I would just give it a try.
2.) We've moved all our high-load Tomcat/Weblogic servers onto Linux-2.6.18 (Opteron boxes), from Windows2000 Advanced Server. For good reasons ;)
lg Clemens
