PM70270: A LOWER BUFFER HIT RATIO OR MORE SYNCHRONOUS I/O IF VPSEQT IS SET TO A SMALL VALUE

A fix is available

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APAR status

  • Closed as program error.

Error description

  • When a random Getpage buffer miss resulted in DB2 stealing a
    buffer from the sequential LRU chain, DB2 did not remove the
    buffer from the sequential LRU chain when it should.  This meant
    that random pages were more likely constricted by VPSEQT.
    Therefore in some cases, recently used buffers were stolen more
    quickly than less recently used buffers, resulting in a a lower
    buffer hit ratio or more synchronous I/O.   The impact of this
    problem is relatively small if the default VPSEQT value of 80%
    is used, but the impact is likely to be large if VPSEQT is set
    

Local fix

Problem summary

  • ****************************************************************
    * USERS AFFECTED: All DB2 users.                               *
    ****************************************************************
    * PROBLEM DESCRIPTION: A lower buffer pool hit ratio or more   *
    *                      synchronous I/O.                        *
    ****************************************************************
    * RECOMMENDATION:                                              *
    ****************************************************************
    When a random GetPage operation steals a buffer from the
    sequential LRU (SLRU) chain, DB2 does not reclassify the stolen
    buffer. In rare cases, it may result in a lower buffer pool hit
    ratio or more synchronous I/O.
    

Problem conclusion

  • DB2 has been fixed to reclassify a buffer that is stolen from
    the SLRU chain for a random GetPage operation.
    

Temporary fix

  • *********
    * HIPER *
    *********
    

Comments

APAR Information

  • APAR number

    PM70270

  • Reported component name

    DB2 OS/390 & Z/

  • Reported component ID

    5740XYR00

  • Reported release

    910

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    YesHIPER

  • Special Attention

    NoSpecatt

  • Submitted date

    2012-08-03

  • Closed date

    2012-10-09

  • Last modified date

    2012-11-01

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

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

    UK82555 UK82556

Modules/Macros

  •    DSNB1CMS DSNB1GET
    

Fix information

  • Fixed component name

    DB2 OS/390 & Z/

  • Fixed component ID

    5740XYR00

Applicable component levels

  • RA10 PSY UK82555

       UP12/10/28 P F210

  • R910 PSY UK82556

       UP12/10/28 P F210

Fix is available

  • Select the PTF appropriate for your component level. You will be required to sign in. Distribution on physical media is not available in all countries.



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Document information


More support for:

DB2 for z/OS

Software version:

910

Reference #:

PM70270

Modified date:

2012-11-01

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