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PM13232: WLM Feedback Mechanism fails to reset weights properly

Fixes are available

7.0.0.15: WebSphere Application Server V7.0 Fix Pack 15 for AIX
7.0.0.15: Java SDK 1.6 SR9 Cumulative Fix for WebSphere Application Server
7.0.0.15: WebSphere Application Server V7.0 Fix Pack 15 for HP-UX
7.0.0.15: WebSphere Application Server V7.0 Fix Pack 15 for IBM i
7.0.0.15: WebSphere Application Server V7.0 Fix Pack 15 for Linux
7.0.0.15: WebSphere Application Server V7.0 Fix Pack 15 for Solaris
7.0.0.15: WebSphere Application Server V7.0 Fix Pack 15 for Windows
7.0.0.17: WebSphere Application Server V7.0 Fix Pack 17
7.0.0.17: Java SDK 1.6 SR9 FP1 Cumulative Fix for WebSphere Application Server
7.0.0.19: WebSphere Application Server V7.0 Fix Pack 19
7.0.0.21: WebSphere Application Server V7.0 Fix Pack 21
7.0.0.23: WebSphere Application Server V7.0 Fix Pack 23
7.0.0.25: WebSphere Application Server V7.0 Fix Pack 25
7.0.0.27: WebSphere Application Server V7.0 Fix Pack 27
7.0.0.29: WebSphere Application Server V7.0 Fix Pack 29
7.0.0.31: WebSphere Application Server V7.0 Fix Pack 31
7.0.0.27: Java SDK 1.6 SR13 FP2 Cumulative Fix for WebSphere Application Server
7.0.0.33: WebSphere Application Server V7.0 Fix Pack 33
7.0.0.35: WebSphere Application Server V7.0 Fix Pack 35
7.0.0.37: WebSphere Application Server V7.0 Fix Pack 37
7.0.0.39: WebSphere Application Server V7.0 Fix Pack 39
7.0.0.41: WebSphere Application Server V7.0 Fix Pack 41
7.0.0.43: WebSphere Application Server V7.0 Fix Pack 43
7.0.0.45: WebSphere Application Server V7.0 Fix Pack 45
7.0.0.19: Java SDK 1.6 SR9 FP2 Cumulative Fix for WebSphere Application Server
7.0.0.21: Java SDK 1.6 SR9 FP2 Cumulative Fix for WebSphere
7.0.0.23: Java SDK 1.6 SR10 FP1 Cumulative Fix for WebSphere
7.0.0.25: Java SDK 1.6 SR11 Cumulative Fix for WebSphere Application Server
7.0.0.27: Java SDK 1.6 SR12 Cumulative Fix for WebSphere Application Server
7.0.0.29: Java SDK 1.6 SR13 FP2 Cumulative Fix for WebSphere Application Server
7.0.0.45: Java SDK 1.6 SR16 FP60 Cumulative Fix for WebSphere Application Server
7.0.0.31: Java SDK 1.6 SR15 Cumulative Fix for WebSphere Application Server
7.0.0.35: Java SDK 1.6 SR16 FP1 Cumulative Fix for WebSphere Application Server
7.0.0.37: Java SDK 1.6 SR16 FP3 Cumulative Fix for WebSphere Application Server
7.0.0.39: Java SDK 1.6 SR16 FP7 Cumulative Fix for WebSphere Application Server
7.0.0.41: Java SDK 1.6 SR16 FP20 Cumulative Fix for WebSphere Application Server
7.0.0.43: Java SDK 1.6 SR16 FP41 Cumulative Fix for WebSphere Application Server

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APAR status

  • Closed as program error.

Error description

  • The WeightnceedProportional Algorithm for Proxy creates a
    routing imbalance.
    

Local fix

Problem summary

  • ****************************************************************
    * USERS AFFECTED:  Users of IBM WebSphere Application          *
    *                  Server V7.0 Proxy Server with multiple      *
    *                  applications installed to the cluster       *
    *                  members.                                    *
    ****************************************************************
    * PROBLEM DESCRIPTION: Workload management (WLM) Feedback      *
    *                      Mechanism fails to reset weights        *
    *                      properly                                *
    ****************************************************************
    * RECOMMENDATION:                                              *
    ****************************************************************
    There is code within the WLM algorithms which, by default,
    will attempt to slightly modify the internally held weight
    distribution of the cluster members in order to provide better
    overall throughput. Members with a larger backlog of requests
    will see less load in the short term versus the members with a
    smaller backlog of requests.
    
    When using a WebSphere Application Server Proxy server and
    routing requests concurrently to multiple applications
    installed on the same cluster members, and primarily when the
    clusters only contain two members, it is possible for the
    feedback mechanism to get into a bad state and route all the
    requests for one application to only one cluster member for
    extended periods of time (anywhere from multiple minutes to
    multiple hours).
    
    Although it would be possible for this problem to occur with
    more than two members in the cluster, it would be extremely
    unlikely.
    

Problem conclusion

  • Evaluation of the code indicated that the problem with the
    feedback mechanism in this particular Proxy Server scenario
    required a solution which would not necessarily be ideal for
    other routing scenarios.  The solution was to create a custom
    property to force certain behavior out of the feedback
    mechanism, which would prevent the code from getting into a
    state of sending requests to only one member for extended
    periods of time.
    
    In order to enable and use the custom property, you must take
    the following steps:
    
    In the administrative  console click on "System Administration"
    on the left side, click on "Cell" underneath that, then click
    on "Custom Properties" in the middle frame.
    
    You'll want to create the following custom property:
    
    IBM_CLUSTER_FORCE_FEEDBACK with a value of true.
    
    Save that change and sync the config with the nodes, then
    shut everything down (dmgr NA and servers) and start it up
    again. If you have WLM trace enabled, you should see this in
    the trace logs:
    
    [3/23/06 15:17:59:828 CST] 0000000a ProcessRuntim >
    loadCustomProperties Entry
    [3/23/06 15:17:59:828 CST] 0000000a ProcessRuntim 1
    Loaded custom property
    IBM_CLUSTER_FORCE_FEEDBACK
    true
    
    The fix for this APAR is currently targeted for inclusion in
    fix pack 7.0.0.15.  Please refer to the Recommended Updates
    page for delivery information:
    http://www.ibm.com/support/docview.wss?rs=180&uid=swg27004980
    

Temporary fix

Comments

APAR Information

  • APAR number

    PM13232

  • Reported component name

    WEBSPHERE APP S

  • Reported component ID

    5724J0800

  • Reported release

    700

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt

  • Submitted date

    2010-04-27

  • Closed date

    2010-10-21

  • Last modified date

    2010-10-21

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

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

Fix information

  • Fixed component name

    WEBSPHERE APP S

  • Fixed component ID

    5724J0800

Applicable component levels

  • R700 PSY

       UP

[{"Business Unit":{"code":"BU053","label":"Cloud & Data Platform"},"Product":{"code":"SSEQTP","label":"WebSphere Application Server"},"Platform":[{"code":"PF025","label":"Platform Independent"}],"Version":"7.0","Line of Business":{"code":"LOB45","label":"Automation"}}]

Document Information

Modified date:
24 October 2021