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  1. JDK
  2. JDK-8281743

Missing information about how and why to specify MMU in tuning guide



    • Type: Bug
    • Status: Closed
    • Priority: P2
    • Resolution: Duplicate
    • Affects Version/s: 9, 11, 17, 18, 19
    • Fix Version/s: 19
    • Component/s: hotspot
    • Labels:
    • Subcomponent:


      In the JDK8 tuning guide there has been a paragraph explaining how setting the MMU using MaxGCPauseMillis/GCPauseIntervalMillis works (https://docs.oracle.com/javase/8/docs/technotes/guides/vm/gctuning/g1_gc.html#pause_time_goal )

      "Pause Time Goal

      Set a pause time goal for G1 with the flag MaxGCPauseMillis. G1 uses a prediction model to decide how much garbage collection work can be done within that target pause time. At the end of a collection, G1 chooses the regions to be collected in the next collection (the collection set). The collection set will contain young regions (the sum of whose sizes determines the size of the logical young generation). It is partly through the selection of the number of young regions in the collection set that G1 exerts control over the length of the GC pauses. You can specify the size of the young generation on the command line as with the other garbage collectors, but doing so may hamper the ability of G1 to attain the target pause time. In addition to the pause time goal, you can specify the length of the time period during which the pause can occur. You can specify the minimum mutator usage with this time span (GCPauseIntervalMillis) along with the pause time goal. The default value for MaxGCPauseMillis is 200 milliseconds. The default value for GCPauseIntervalMillis (0) is the equivalent of no requirement on the time span."

      The current tuning guide/documentation mentions GCPauseIntervalMillis only in passing, and uses a wrong name too (as "PauseTimeIntervalMillis").

      Fix this.


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              Unassigned Unassigned
              tschatzl Thomas Schatzl
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