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PI29726: HIGH CPU IN THE IRLM AND XCFAS ADDRESS SPACES FOLLOWING AN INSERT AND A DELETE IN THE SAME COMMIT SCOPE

A fix is available

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APAR status

  • Closed as program error.

Error description

  • When there is an insert and a delete in the same commit
    scope against a tablespace using page level locking, it
    is possible for DB2 to overload IRLM and XES with alter
    requests for the lock.
    

Local fix

  • Change the logic for DB2 to not send SET/INS on page level
    lock requests.
    

Problem summary

  • ****************************************************************
    * USERS AFFECTED: DB2 10 for z/OS users of                     *
    *                 segmented or UTS table space with page       *
    *                 level locking.                               *
    ****************************************************************
    * PROBLEM DESCRIPTION: When an insert transaction requests     *
    *                      a page lock, and the transaction        *
    *                      already holds the lock from a prior     *
    *                      delete, it will trigger IRLM to alter   *
    *                      the lock from a delete type to an       *
    *                      insert type. If the global lock         *
    *                      manager is on a different member, this  *
    *                      alter request can cause the coupling    *
    *                      facility to reject the alter, which     *
    *                      in turn causes IRLM to reject the page  *
    *                      lock request. The INSERT then           *
    *                      continues to request page locks, and    *
    *                      subsequent inserts do the same. When    *
    *                      there is a high volume of inserts       *
    *                      following a delete in the same commit   *
    *                      scope, it can result in high CPU in     *
    *                      the IRLM and XCFAS address spaces.      *
    *                      This problem can also happen when       *
    *                      there is a high volume of DELETEs       *
    *                      following an INSERT in the same commit  *
    *                      scope. This only happens with page      *
    *                      level locking.                          *
    ****************************************************************
    * RECOMMENDATION:                                              *
    ****************************************************************
    The page lock request by the INSERT transaction can be
    falsely rejected when there is delete transaction already held
    a page lock on the same data page within the same commit scope.
    Under this circumstance, the page lock request by the INSERT
    transaction will trigger IRLM to alter or verify lock holding
    state with CF. As a result, high CPU in the IRLM and XCFAS
    address space can occurr when there is high volume of
    DELETE follow by INSERT within the same commit scope.
    

Problem conclusion

  • DB2 code is changed to avoid sending the alter requests which
    cause the coupling facility to falsely reject page lock
    requests.
    

Temporary fix

Comments

APAR Information

  • APAR number

    PI29726

  • Reported component name

    DB2 OS/390 & Z/

  • Reported component ID

    5740XYR00

  • Reported release

    A10

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt / Xsystem

  • Submitted date

    2014-11-14

  • Closed date

    2014-12-11

  • Last modified date

    2015-01-02

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

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

    UI23808

Modules/Macros

  •    DSNISGRT
    

Fix information

  • Fixed component name

    DB2 OS/390 & Z/

  • Fixed component ID

    5740XYR00

Applicable component levels

  • RA10 PSY UI23808

       UP14/12/30 P F412

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

Modified date:
06 May 2020