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Date: Wed, 20 Feb 2013 19:52:56 +1100
Subject: Re: Help in diagnosing server unresponsiveness
From: Zoran Avtarovski <zoran@sparecreative.com>
To: Tomcat Users List <users@tomcat.apache.org>
Message-ID: <CD4AD867.3760D%zoran@sparecreative.com>
Thread-Topic: Help in diagnosing server unresponsiveness
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 <CAGV1rDJgOzAw0UzaBdQXZjisfpO6A+4UPEKneL4OFfC3D7bdaw@mail.gmail.com>
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Hi Guys,

It's been a while but the nature of this problem means it may be a while
between crashes. But we just had a big one which hung the system and
required a reboot.

I have changed the tomcat options as follows inline with all the advice
and material I read to be as follows:

-server -Xms1460m -Xmx11460m -Djava.awt.headless=true
-XX:+UseCompressedOops -XX:+UseConcMarkSweepGC -XX:+CMSIncrementalMode
-XX:MaxPermSize=512M -XX:NewSize=4500m -XX:+CMSClassUnloadingEnabled
-XX:+UseConcMarkSweepGC -XX:-UseGCOverheadLimit
-XX:CMSInitiatingOccupancyFraction=80 -verbose:gc -XX:+PrintGCDetails
-XX:+PrintGCTimeStamps -Xloggc:/usr/local/tomcat/logs/gc.log


The garbage collection log had the following details just prior to the
crash:

4163.757: [GC [1 CMS-initial-mark: 0K(5376K)] 1834200K(4152576K),
1.9237250 secs] [Times: user=1.92 sys=0.00, real=1.92 secs]
4165.682: [CMS-concurrent-mark-start]
4165.834: [CMS-concurrent-mark: 0.152/0.152 secs] [Times: user=0.15
sys=0.00, real=0.16 secs]
4165.834: [CMS-concurrent-preclean-start]
4165.849: [CMS-concurrent-preclean: 0.015/0.015 secs] [Times: user=0.01
sys=0.00, real=0.01 secs]
4165.849: [CMS-concurrent-abortable-preclean-start]
 CMS: abort preclean due to time 4171.285:
[CMS-concurrent-abortable-preclean: 5.035/5.436 secs] [Times: user=5.05
sys=0.00, real=5.44 secs]
4171.285: [GC[YG occupancy: 1834200 K (4147200 K)]4171.286: [Rescan
(parallel) , 1.5184720 secs]4172.804: [weak refs processing, 0.0001420
secs]4172.804: [class unloading, 0.0118860 secs]4172.816: [scrub symbol &
string tables, 0.0141570 secs] [1 CMS-remark: 0K(5376K)]
1834200K(4152576K), 1.5484470 secs]


And the JavaMelody monitoring indicated the crash occurred at the same
time as garbage collection took place. Basically the Garbage collector
time chart peaked at 20 and ran for about 15minutes.


I has a look at the garbage collector chart over a longer period and when
the collector runs more frequently it appears to be more stable.

Any advice on where to go next?


Z.


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