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PI20352: INCREASED CPU (SRB) IN DIST WHEN USING HIGH PERFORMANCE DBATS

A fix is available

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APAR status

  • Closed as unreproducible in next release.

Error description

  • DB2DDF DB2HIGHPERFDBAT defect pi20352 dpi20352
    When a connection terminates before using a high performance
    DBAT 200 times, DDF terminates the DBAT rather than pooling
    it.  This forces DDF to create new high performance DBATs more
    frequently than is necessary.  This behavior causes an increase
    in non-enclave (non-preemptible) SRB time in the DDF address
    space.
    

Local fix

Problem summary

  • ****************************************************************
    * USERS AFFECTED: All Distributed Data Facility (DDF) users    *
    *                 who are using, or plan to use,               *
    *                 High Performance DBAT support.  That is,     *
    *                 users which operate DDF with option          *
    *                 PKGREL(BNDOPT).                              *
    ****************************************************************
    * PROBLEM DESCRIPTION: New function is being provided to       *
    *                      reduce the CPU required to manage       *
    *                      High Performance DBATs.                 *
    ****************************************************************
    * RECOMMENDATION:                                              *
    ****************************************************************
    DB2 10 for z/OS introduced a new DDF server thread processing
    mode called High Performance DBATs.  If DDF has been modified
    to operate in this mode (-MODIFY DDF PKGREL(BNDOPT)), DDF keeps
    a client connection attached to its DBAT for up to 200 units-
    of-work.  The DBAT must have allocated a package which was
    bound with the RELEASE DEALLOCATE bind option to activate high
    performance DBAT processing.  Also, the 200 units-of-work must
    not hold resources, such as open WITH HOLD cursors, declared
    global temporary tables, and/or LOB locators, past any
    transaction end of unit-of-work.
    Currently, as soon as the client connection terminates, DDF
    also terminates the associated DBAT if the DBAT has operated
    in high performance DBAT mode.  That is, DDF will not attempt
    to pool the high performance DBAT regardless of how many
    units-of-work the connection/DBAT has processed.  If a client
    connection terminates before using a high performance DBAT for
    more than 200 units-of-work, DDF could potentially use more CPU
    to create new DBATs for the benefit of subsequent connections.
    

Problem conclusion

Temporary fix

Comments

  • DB2 has been changed to pool a high performance DBAT when the
    associated connection terminates.  DDF will still only allow
    the DBAT to be pooled for up to 200 units-of-work.  The
    improved availability of pooled DBATs will help reduce the CPU
    cost that would otherwise be required to create a new DBAT when
    needed.
    Also, in order to prevent a high performance DBAT from being
    pooled indefinitely, or until DDF has been recycled, when the
    POOL THREAD TIMEOUT (DSN6FAC POOLINAC) subsystem parameter is
    set to 0, DB2 will internally apply a default value of 120
    seconds.
    ž**** PE15/05/12 FIX IN ERROR. SEE APAR PI31597  FOR DESCRIPTION
    

APAR Information

  • APAR number

    PI20352

  • Reported component name

    DB2 OS/390 & Z/

  • Reported component ID

    5740XYR00

  • Reported release

    A10

  • Status

    CLOSED UR1

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    YesSpecatt / New Function

  • Submitted date

    2014-06-18

  • Closed date

    2014-07-23

  • Last modified date

    2015-05-12

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

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

    UI19900 UI19901

Modules/Macros

  •    DSNLEDDA DSNLQCTL DSNLQDIS
    

Fix information

  • Fixed component name

    DB2 OS/390 & Z/

  • Fixed component ID

    5740XYR00

Applicable component levels

  • RA10 PSY UI19900

       UP14/08/07 P F408

  • RB10 PSY UI19901

       UP14/08/07 P F408

Fix is available

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Document information

More support for: DB2 for z/OS

Software version: A10

Reference #: PI20352

Modified date: 12 May 2015


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