IBM Support

IV47984: LONG GC PAUSE TIMES WHEN USING WIDE CLASS HIERARCHIES

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APAR status

  • Closed as program error.

Error description

  • Error Message: The problem presents as long pauses during which
    the application appears to hang. Taking a verbose GC log shows
    that each pause is associated with an unusually long GC event.
    The problem is associated with the use of very wide class
    inheritance trees, often due to the use of an application
    framework with an abstract base class which is sub-classed many
    thousands of times by the application.
    .
    Stack Trace: N/A
    .
    

Local fix

  • The problem can be avoided by disabling the use of class
    hierarchy information during JIT compilation by using the
    following Java command line option:
    -Xjit:disableCHOpts,disableCHTable
    

Problem summary

  • Very wide class hierarchies cause the JIT to collect excessive
    amounts of metadata about the resulting compiled code if certain
    optimisations are used. This metadata has to be cleaned up after
    class unloading which results in the long GC times.
    

Problem conclusion

  • This defect will be fixed in:
    6.0.0 SR15
    7.0.0 SR6
    6.0.1 SR7
    5.0.0 SR16 FP4
    .
    The JIT has been modified to avoid collecting the metadata if a
    wide class hierarchy is detected for the method being compiled.
    

Temporary fix

Comments

APAR Information

  • APAR number

    IV47984

  • Reported component name

    JIT

  • Reported component ID

    620700124

  • Reported release

    600

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt

  • Submitted date

    2013-09-06

  • Closed date

    2013-09-06

  • Last modified date

    2013-10-18

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

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

    IV47990

Fix information

  • Fixed component name

    JIT

  • Fixed component ID

    620700124

Applicable component levels

  • R600 PSY

       UP

  • R260 PSY

       UP

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Document Information

Modified date:
18 October 2013