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PH22382: IBM MQ 9.0 CLIENT CONNECTIONS UNDER LOAD ENCOUNTER MQRC 2538 AFTER ISSUING MQCONN

A fix is available

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APAR status

  • Closed as program error.

Error description

  • Change Team finds that during periods of high volume connection
    requests, two tasks (listener and nameserver TCBs) may not
    be dispatched with sufficient frequency in order to service the
    incoming backlog
    .
    Additional keywords:
    2538 MQRC_HOST_NOT_AVAILABLE
    

Local fix

Problem summary

  • ****************************************************************
    * USERS AFFECTED: All users of IBM MQ for z/OS Version 9       *
    *                 Release 0 Modification 0.                    *
    ****************************************************************
    * PROBLEM DESCRIPTION: When a large number of clients attempt  *
    *                      to connect simultaneously, some of the  *
    *                      clients receive MQRC_HOST_NOT_AVAILABLE *
    *                      (2538).                                 *
    ****************************************************************
    A large number of clients attempted to connect to the listener
    at the same time. During processing of each connection,
    inet_ntop was scheduled to run on the nameserver task, and the
    listener task was suspended waiting to be redispatched when the
    request completed.
    While the listener task was suspended waiting on the nameserver
    task, incoming connections were queued up, until the number of
    queued connections reached the TCP socket backlog limit.
    At this point any further connections fail with MQRC 2538
    immediately, without being processed by the MQ listener task.
    

Problem conclusion

  • The listener is changed to call inet_ntop and inet_pton inline
    rather than passing a request to the nameserver task and waiting
    for a response.
    
    In addition the socket backlog value specified on the listen()
    call made by the listener is increased.
    

Temporary fix

Comments

APAR Information

  • APAR number

    PH22382

  • Reported component name

    IBM MQ Z/OS V9

  • Reported component ID

    5655MQ900

  • Reported release

    000

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt / Xsystem

  • Submitted date

    2020-02-19

  • Closed date

    2020-06-26

  • Last modified date

    2020-09-01

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

    PH12344

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

    UI70282

Modules/Macros

  • CSQIRECP CSQMSTRT CSQXBNT1 CSQXCCXT CSQXCLIT CSQXLMOD CSQXPENT
    CSQXPIPI CSQXSFRE CSQXSGET CSQXTNSC
    

Fix information

  • Fixed component name

    IBM MQ Z/OS V9

  • Fixed component ID

    5655MQ900

Applicable component levels

  • R000 PSY UI70282

       UP20/08/08 P F008

Fix is available

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Document Information

Modified date:
03 September 2020