Need help on long minor GC pause

[Avinash Mishra]

Hi folks,

Thanks for the quick feedback. We got lucky with the issue and got these logs today:

120850.013: [ParNew120865.142: [SoftReference, 0 refs, 0.0000052 secs]120865.142: [WeakReference, 1 refs, 0.0000022 secs]120865.142: [FinalReference, 0 refs, 0.0000014 secs]120865.142: [PhantomReference, 2 refs, 0.0000018 secs]120865.142: [JNI Weak Reference, 0.0000014 secs]: 59007K->6528K(59008K), 15.1290884 secs] 893600K->843004K(1042048K)After GC:
Statistics for BinaryTreeDictionary:
------------------------------------
Total Free Space: 37142932
Max   Chunk Size: 19517862
Number of Blocks: 20
Av.  Block  Size: 1857146
Tree      Height: 8
After GC:
Statistics for BinaryTreeDictionary:
------------------------------------
Total Free Space: 3635496
Max   Chunk Size: 3634176
Number of Blocks: 3
Av.  Block  Size: 1211832
Tree      Height: 2
, 15.1295291 secs] [Times: user=0.13 sys=0.00, real=15.13 secs] 


So you were probably right about swapping to be the potential issue. The strange thing is that its we have 8GB of RAM on the server and only 2.5 GB is used.

Could you please suggest us on how can we confirm if its a swapping issue (we do have perfmons). Also, please suggest how we can fix this problem on Windows server.

Regards,
Avinash



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Today's Topics:

   1. Re: Need help on long minor GC pause (W?thrich J?rg)


----------------------------------------------------------------------

Message: 1
Date: Wed, 11 Sep 2013 11:54:16 +0200
From: W?thrich J?rg <jwu at gmx.ch>
Subject: Re: Need help on long minor GC pause
To: hotspot-gc-use at openjdk.java.net
Message-ID: <52303DC8.5000801 at gmx.ch>
Content-Type: text/plain; charset="iso-8859-1"

Hi Avinash,

If it turns out to be a fragmentation issue, you might want to consider 
upgrading to a newer java version, because 1.6u25 and above have serious 
improvements concerning fragmentation 
(http://blog.ragozin.info/2011/10/java-cg-hotspots-cms-and-heap.html).

One place where I saw very long pauses with fragmentation was when 
concurrent mode failures occurred. I am not sure if fragmentation 
affects minor GCs so much.

You might also want to follow another lead: swapping. GC logs also 
contain the "|Times:user=2.19sys=1.35,real=385.50secs]" in the end of 
the lines. If "real" is much longer than "user"+"sys" your system might 
be swapping.|
|||
Regards,
J?rg

|Am 11.09.2013 10:24, schrieb Avinash Mishra:
> Hi folks,
>
> We are facing a strange issue where the minor GC gets stuck for 
> several seconds:
>
> 734827.324: [GC 639235K->587610K(1042048K), 2.4140118 secs]
> 734846.488: [GC 640090K->589859K(1042048K), 22.1046232 secs]
> 734949.577: [GC 642339K->590078K(1042048K), 12.2527731 secs]
> 735045.592: [GC 642558K->591084K(1042048K), 0.1158979 secs]
> Our Java configuration is something like this:
>
> java -Xms1024m -Xmx1024m -XX:+UseConcMarkSweepGC -cp %MY_CLASSPATH% 
> com.myclass
>
> We are using Java 1.6u24 and the application is running on a Windows 
> 2003 server.
>
> The issue is specific to a couple of servers at a customer site and 
> nowhere else. The servers here run fine for up to some 45 days when 
> the issue shows up.
>
> From the logs(above) it seems that there is plenty of old space 
> available on heap so we have ruled out concurrent failures. We are 
> looking into fragmentation as the potential root cause. We have 
> enabled these traces to confirm if we have a fragmentation issue
>
> -XX:+PrintGCDetails
> -XX:+PrintPromotionFailure
> -XX:PrintFLSStatistics=1
>
> From these logs we are monitoring "Max chunk available" and look for a 
> decrease in trend to determine if the servers are heading towards a 
> fragmentation problem. Please let me know if anything else is required 
> to confirm on fragmentation issue and if there is a a way to confirm 
> it sooner instead of waiting for couple of months.
>
> Please let me know if you have any other pointers on potential root cause.
>
> Thanks,
> Avinash
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