longer ParNew collection in JDK8?

[Joy Xiong]

Hi Jon,
Yes, most objects in my application die young and very little promoted. As you can see from the attached figure (the occupied heap size from Sep 28 to Nov 11), CMS happened very rare. However, it seems two releases do not have much difference in promotion rate, as they have same number of CMS in the log.
We have the same JVM parameters for both releases as below:
CommandLine flags: -XX:+AlwaysPreTouch -XX:CMSInitiatingOccupancyFraction=70 -XX:ErrorFile=logs/hs_err.log -XX:InitialHeapSize=34271657984 -XX:+ManagementServer -XX:MaxHeapSize=34271657984 -XX:MaxNewSize=2147483648 -XX:NewSize=2147483648 -XX:OldPLABSize=16 -XX:+PrintGC -XX:+PrintGCApplicationConcurrentTime -XX:+PrintGCApplicationStoppedTime -XX:+PrintGCDateStamps -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:+PrintTenuringDistribution -XX:SurvivorRatio=2 -XX:+UnlockDiagnosticVMOptions -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseConcMarkSweepGC -XX:+UseParNewGC
thanks,-Joy 

     On Monday, February 2, 2015 10:06 AM, Jon Masamitsu <jon.masamitsu at oracle.com> wrote:
   

  Joy,
 
 Is your application such that most everything dies in the
 young generation and very little is promoted?  If yes,
 do you know if there is a difference in how much is
 promoted between the two releases?
 
 Jon
 
 On 01/29/2015 10:27 AM, Joy Xiong wrote:
  
    
  Hi, 
  We recently move our services from JDK6 to JDK8, but observe longer ParNew GC pause in JDK8. For example, the pause time increase from 27ms to 43ms in one service. The service has the JVM parameters as below:  -Xms32684m -Xmx32684m -XX:NewSize=2048m -XX:MaxNewSize=2048m -XX:+UseConcMarkSweepGC -XX:+UseParNewGC -XX:CMSInitiatingOccupancyFraction=70 -XX:SurvivorRatio=2 -XX:+AlwaysPreTouch -XX:+UseCompressedOops -XX:+PrintTenuringDistribution -XX:+PrintGCDetails -XX:+PrintGCDateStamps -Xloggc:logs/gc.log -XX:+PrintGCApplicationStoppedTime -XX:+PrintGCApplicationConcurrentTime 
   Is this longer ParNew pause expected? Any suggestions to mitigate the longer pause? 
  thanks, -Joy    
  
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