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POJava vm slows down with all threads busy with String operations
 

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  1. POJava vm slows down with all threads busy with String operations
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    <p>I am running into a very peculiar issue. My tomcat runs perfectly at about 25% CPU 24/7, but some days my CPU shoots up to 60% and the system grinds to a halt and fails to recover.</p> <p>When I take a thread dump during the slow down almost all the threads are busy with some kind of String or related operation. </p> <p>There are no OutOfMemory errors or any exceptions being thrown, all requests are still handled but response times deteriorate to the nth degree where even a sub second request slows down to take 60 seconds and more. </p> <p>My server config is as follows:</p> <pre> Ubuntu 12.04.2 LTS Linux 3.2.0-38-virtual #60-Ubuntu SMP x86_64 x86_64 x86_64 GNU/Linux </pre> <pre> java version "1.7.0_13" Java(TM) SE Runtime Environment (build 1.7.0_13-b20) Java HotSpot(TM) 64-Bit Server VM (build 23.7-b01, mixed mode) </pre> <pre> export JAVA_OPTS='-server -Xms18g -Xmx18g -XX:MaxPermSize=512m -XX:ThreadStackSize=512 -XX:NewRatio=1 -XX:SurvivorRatio=4 -XX:+UseConcMarkSweepGC -XX:+UseParNewGC -XX:+CMSClassUnloadingEnabled -Xloggc:/usr/tomcat/logs/gc.log -XX:+PrintGCDetails -XX:+PrintGCDateStamps -XX:+PrintTenuringDistribution -Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.port=9999 -Dcom.sun.management.jmxremote.authenticate=false -Dcom.sun.management.jmxremote.ssl=false -Djava.awt.headless=true' </pre> <p><strong><a href="https://www.dropbox.com/s/e8kvnko76o6e4mh/threadDump.txt?dl=0" rel="nofollow">Click here to download thread dump. I have removed the bulk of the threads and their stackTraces</a></strong></p> <p><strong><a href="https://www.dropbox.com/s/67esde7nfys3vmd/vmstat.2014-08-19.log?dl=0" rel="nofollow">Click here to download vmstat log</a></strong></p> <p><strong><a href="https://www.dropbox.com/s/gwiloe3ooita0sx/gc.2014-08-19.log?dl=0" rel="nofollow">Click here to download gc log</a></strong></p> <p>Any ideas as to the cause of this? Thanks</p>
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    1. USRudi Strydom
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    1. CODo you get more requests at those times? Do you have network graphs to compare to?
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      1. USBrendan Long
    2. COAny chance this being stop-the-world GC? Do you log gc events?
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      1. USmindas
    3. COmaybe your app is happy running with a set of usual chars, then once in a blue moon an unusual char shows up, which somehow disturbed the vm optimization. you can test this theory by feeding different chars and see if any char would trigger the problem. if it's true it should be a vm bug.
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