title: Java vm slows down with all threads busy with String operations
body: <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>