Continous FULL GC

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Performance and scalability: Continous FULL GC

  1. Continous FULL GC (1 messages)

    We have an application running on IBM websphere server with the following JVM and heap settings

    Heap Settings
    Min Hep : 750MB, MaxHeap : 1500 MB

    JVM Settings
    -XX:PermSize=64m -XX:MaxPermSize=128m -XX:+PrintGCTimeStamps -XX:+PrintHeapAtGC

    In the verbose log file we observed that FULL GC is triggered even though we have enough memory in all generations (young,old, permannent) of JVM. Here is a sample output from the GC log file

    } {Heap before GC invocations=1420:
    Heap
    def new generation total 83136K, used 217K [0x94400000, 0x997a0000, 0x9eaa0000)
    eden space 80640K, 0% used [0x94400000, 0x94436570, 0x992c0000)
    from space 2496K, 0% used [0x99530000, 0x99530000, 0x997a0000)
    to space 2496K, 0% used [0x992c0000, 0x992c0000, 0x99530000)
    tenured generation total 682688K, used 115942K [0x9eaa0000, 0xc8550000, 0xf2000000)
    the space 682688K, 16% used [0x9eaa0000, 0xa5bd9a08, 0xa5bd9c00, 0xc8550000)
    compacting perm gen total 131072K, used 40314K [0xf2000000, 0xfa000000, 0xfa000000)
    the space 131072K, 30% used [0xf2000000, 0xf475ebc0, 0xf475ec00, 0xfa000000)
    64557.286: [Full GC 116159K->115961K(765824K), 2.1373354 secs] Heap after GC invocations=1421:
    Heap
    def new generation total 83136K, used 0K [0x94400000, 0x997a0000, 0x9eaa0000)
    eden space 80640K, 0% used [0x94400000, 0x94400000, 0x992c0000)
    from space 2496K, 0% used [0x99530000, 0x99530000, 0x997a0000)
    to space 2496K, 0% used [0x992c0000, 0x992c0000, 0x99530000)
    tenured generation total 682688K, used 115961K [0x9eaa0000, 0xc8550000, 0xf2000000)
    the space 682688K, 16% used [0x9eaa0000, 0xa5bde658, 0xa5bde800, 0xc8550000)
    compacting perm gen total 131072K, used 40314K [0xf2000000, 0xfa000000, 0xfa000000)
    the space 131072K, 30% used [0xf2000000, 0xf475ebc0, 0xf475ec00, 0xfa000000)
    }

    We started observing this behaviour only after we started using webservice (HTTP) as communication protocal instead of RMI/IIOP. Is there any specific reason for this kind of bahaviour. Do we need to make any special settings to avoid this behavior.

    Threaded Messages (1)

  2. rmi gc?[ Go to top ]

    if its occuring every minute, it might be the RMI GC which is enabled by default. If its appropiate for your application, you should disable your RMI GC thread..

    also, when using such a large VM, you should configure your tenuring thresholds as well to prevent too much leakage from eden to old gen.