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  1. JDK
  2. JDK-6368557

UseParallelGC/Adaptive Size/SurvivorRatio broken

    Details

    • Type: Enhancement
    • Status: Closed
    • Priority: P3
    • Resolution: Won't Fix
    • Affects Version/s: 1.4.2
    • Fix Version/s: None
    • Component/s: hotspot
    • Labels:
    • Subcomponent:
      gc
    • CPU:
      sparc
    • OS:
      solaris_2.5.1

      Description

      Large variation in size of Eden and Survivor with every garbage
      collection. It appears that the VM is unable to adapt to the constant
      load on the system. If we try to turn off the adaptive sizing using -
      XX:-UseAdaptiveSizePolicy then we get bizarre behavior in which the
      Survivor size remains small - resulting in large overflows of objects
      to the Old space. -XX:SurvivorRatio=2, or set to any value, has no
      impact on the space actually allocated for Eden or Survivor. This
      prevents any type of tuning and leads to poor performance,
      particularly with very large heaps.

      /opt/java1.4/bin/java -Xverbosegc -Xmx11m -Xms11m -Xmn3m -
      XX:SurvivorRatio=2 -XX:+UseParallelGC xxx

      <GCH: argXms=11264 >
      <GCH: argXmx=11264 >
      <GCH: optNewSize=3072 >
      <GCH: optMaxNewSize=3072 >
      <GCH: optOldSize=4096 >

      <GCH: optNewRatio=2 >
      <GCH: optSurvivorRatio=2 >

      <GCH: optUseParNewGC=0 >
      <GCH: optUseParallelGC=1 >
      <GCH: optUseAdaptiveSizePolicy=1 >

      <GCH: reservnew=3072 >
      <GCH: initnew=3072 >
      <GCH: reservold=9216 >
      <GCH: initold=8192 >
      <GCH: reservperm=65536 >
      <GCH: initperm=16384 >
      <GCH: survsize=384 > -- this is what we get - much too small!!!
      <GCH: edensize=2304 >

      Problems:-

      1. When I do use UseParallelGC and turn off the adaptive size policy,
      the default calculation makes the Survivor space very small.

      2. When I try to increase the size of the Survivor space using
      SurvivorRatio, I cannot get it to work.

      3. There are wild vacillations in the sizes of Eden and Survivor -
      there seems to be little dampening of this wild behavior.

      4. After the Old space fills up, a Full GC occurs - that's okay. But
      then a couple of minutes later, for no apparent reason, another Full
      GC occurs - and this pattern repeats.

      The net effect is very poor performance.

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              • Assignee:
                jmasa Jon Masamitsu (Inactive)
                Reporter:
                ksoshals Kirill Soshalskiy (Inactive)
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                • Created:
                  Updated:
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