IZ63035: -XSHARECLASSES SLOWDOWN ATTEMPTING TO LOAD CLASS

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APAR status

  • Closed as program error.

Error description

  • Error Message: In rare situations, a thread can take many
    seconds to attempt to load a class when the shared classes
    feature is enabled.
    This normally only occurs when multiple threads are attempting
    to load the same class simultaneously, and the class does not
    exist (java.lang.ClassNotFoundException would eventually be
    thrown).
    .
    Stack Trace: The problem can be identified by observing a thread
    emitting the j9shr.48 tracepoint repeatedly, as in the example
    below:
    j9shr.48   Event       CM access: waiting for another JVM to
    load class - waited 1 times
    j9shr.48   Event       CM access: waiting for another JVM to
    load class - waited 2 times
    j9shr.48   Event       CM access: waiting for another JVM to
    load class - waited 3 times
    j9shr.48   Event       CM access: waiting for another JVM to
    load class - waited 4 times
    .
    

Local fix

  • The problem can be avoided by adding the
    -Xshareclasses:noReduceStoreContention option.  This disables
    the shared classes optimisation causing the problem.  Note that
    enabling this option may result in more time being taken when
    populating a cold cache.
    

Problem summary

  • In rare situations, a thread can take many seconds to attempt to
    load a class when the shared classes feature is enabled.
    
    This normally only occurs when multiple threads are attempting
    to load the same class simultaneously, and the class does not
    exist (java.lang.ClassNotFoundException would eventually be
    thrown).
    

Problem conclusion

  • The JVM has been updated to resolve the performance problem.
    
    This defect will be fixed in:
    5.0.0 SR11 FP1
    

Temporary fix

Comments

APAR Information

  • APAR number

    IZ63035

  • Reported component name

    JAVA 5 J9 COMMO

  • Reported component ID

    620500127

  • Reported release

    500

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt

  • Submitted date

    2009-10-19

  • Closed date

    2009-12-03

  • Last modified date

    2012-06-15

  • APAR is sysrouted FROM one or more of the following:

  • APAR is sysrouted TO one or more of the following:

Fix information

  • Fixed component name

    JAVA 5 J9 COMMO

  • Fixed component ID

    620500127

Applicable component levels

  • R500 PSN

       UP



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Document information


More support for:

Runtimes for Java Technology
Virtual Machine

Software version:

5.0

Reference #:

IZ63035

Modified date:

2012-06-15

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