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II14026: PERFORMANCE DEGRADATION AFTER CONVERTING LLA MANAGED PDS TO LLA MANAGED PDSE

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You can track all active APARs for this component.

APAR status

  • Closed as canceled.

Error description

  • Note: The text of this APAR was updated on 04/09/2012 and
    again on 02/25/2015 to clarify the effect that page fault
    loading has upon LLA and VLF caching, to provide a better
    explanation for how the Binder FETCHOPT parameter affects
    this processing, and to remove incorrect and/or extraneous
    information.
    This update supersedes and corrects the related discussion
    in Redbook SG24-6106, the Partitioned Data Set Extended
    Usage Guide, which contained information based upon the
    original text in this APAR.
    ******************************************************
    Some customers have reported higher I/O rates or performance
    issues after migrating modules from a PDS to a PDSE, because
    the modules were no longer being cached in VLF by LLA even
    though the PDSE library was LLA managed. It was determined
    that the reason that the PDSE program objects (modules) were
    not cached was that the use of page fault loading caused LLA
    to decide that they were not good candidates for the VLF cache.
    -
    Page fault loading is a method chosen by the Loader for large
    modules, where only part of the program is loaded into storage
    initially and the rest is brought in as needed via paging
    operations.  Since only part of the program is loaded into
    storage initially, LLA's staging algorithm may decide that
    the program would not benefit from being cached in VLF.
    Avoiding page fault loading will help LLA to make the best
    decision about whether a module should be cached in VLF.
    -
    The Loader selects which loading method to use based upon the
    the characteristics of the program object to be loaded.  Page
    fault mode may be chosen by the Loader for large program
    objects when *none* of the following conditions exist:
    . the program object is to be fetched from the LNKLST
    . the program object is to be fetched from an HFS
    . the program object is to be loaded to Global (common storage)
    . the program object is to be loaded to a user-supplied address
    . the program object is less than 96k in size
    . the program object was bound with FETCHOPT=(NOPACK,PRIME)
      or FETCHOPT=(PACK,PRIME)
    -
    Binder option FETCHOPT=(NOPACK,PRIME) causes the Loader to
    bring the entire module into storage immediately, and is a
    recommended way of ensuring that the program is not loaded in
    page fault mode if none of the other conditions listed above
    are fulfilled.  This option does not guarantee that a program
    will be cached in VLF.  It only helps LLA to make the best
    determination as to whether caching the program object in VLF
    is appropriate.  Binder option FETCHOPT=(PACK,PRIME) also will
    ensure that page fault loading is not used, but NOPACK should
    provide better performance when PACK is not otherwise required.
    -
    The CSVLLIX1 and CSVLLIX2 exits can be used to tell LLA to
    cache individual modules or modules from specific libraries.
    -
    Note that when a program object resides in a library that
    is not LLA managed, the default Binder option of
    FETCHOPT=(NOPACK,NOPRIME) may provide better performance.
    

Local fix

Problem summary

Problem conclusion

Temporary fix

Comments

APAR Information

  • APAR number

    II14026

  • Reported component name

    V2 LIB INFO ITE

  • Reported component ID

    INFOV2LIB

  • Reported release

    001

  • Status

    CLOSED CAN

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt / Xsystem

  • Submitted date

    2005-04-26

  • Closed date

    2005-04-26

  • Last modified date

    2015-02-25

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

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

Fix information

Applicable component levels



Document information

More support for: z/OS family

Software version: 001

Operating system(s): MVS, OS/390, z/OS

Reference #: II14026

Modified date: 25 February 2015