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IT15752: REVERT TO PREVIOUS METHOD OF CALCULATING ASYNCHRONOUS WRITE TIME FOR DB2 MONITORING

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APAR status

  • Closed as fixed if next.

Error description

  • DB2 Versions 10.1 Fix Pack 5 (APAR IT05851), 10.5 Fix Pack 7
    (IT06005), and 11.1 GA introduced a behavior change in the way
    asynchronous write time is accumulated.  Asynchronous writes are
    submitted in large batches using asynchronous I/O services/APIs
    provided by an operating system.  The approximate previous
    behavior apportioned a pagecleaner EDU's I/O wait time evenly
    across all pages in a batch.  For example, if a batch of 10 I/O
    requests took 10ms to complete, each I/O request/page write
    would be assigned 1ms of the overall 10ms time.
    
    In many cases the apportionment approach masks underlying
    response time issues, and a change was made in the
    above-mentioned DB2 levels to stop splitting a pagecleaner's
    wait time across all pages written, and instead assign the
    entire batch time to each page write request.  In the case where
    a batch of 10 I/O requests took 10ms to complete each "page
    write" would be assigned the full 10ms.  While there is some
    value in providing this information, as it may more accurately
    reflect I/O response time in some storage configurations, it can
    also cause unnecessary concern.  This is due to the much higher
    calculated average asynchronous page write time, which bubbles
    up to overall average page write time.  It is reasonable that a
    large batch of I/Os may incur some overhead and take longer than
    a single I/O, thus the higher reported time may not be a good
    indicator of underlying I/O performance.  In addition, the wait
    time for pagecleaner write activity does not typically impact
    the time a db2agent EDU spends servicing application requests.
    As such, this APAR fix will revert to the former behaviour of
    splitting pagecleaner I/O wait time across the pages involved in
    a batch of asynchronous I/O requests.
    

Local fix

Problem summary

  • ****************************************************************
    * USERS AFFECTED:                                              *
    * ALL                                                          *
    ****************************************************************
    * PROBLEM DESCRIPTION:                                         *
    * See Error Description                                        *
    ****************************************************************
    * RECOMMENDATION:                                              *
    * Upgrade to DB2 V11.1 FP1                                     *
    ****************************************************************
    

Problem conclusion

Temporary fix

Comments

APAR Information

  • APAR number

    IT15752

  • Reported component name

    DB2 FOR LUW

  • Reported component ID

    DB2FORLUW

  • Reported release

    B10

  • Status

    CLOSED FIN

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt / Xsystem

  • Submitted date

    2016-06-15

  • Closed date

    2017-01-12

  • Last modified date

    2017-01-12

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

    IT15748

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

Fix information

Applicable component levels

[{"Business Unit":{"code":"BU053","label":"Cloud & Data Platform"},"Product":{"code":"SSEPGG","label":"Db2 for Linux, UNIX and Windows"},"Platform":[{"code":"PF025","label":"Platform Independent"}],"Version":"11.1","Line of Business":{"code":"LOB10","label":"Data and AI"}}]

Document Information

Modified date:
29 June 2020