PH12344: IBM MQ 9.1 CLIENT CONNECTIONS UNDER LOAD ENCOUNTER MQRC 2538 AFTER ISSUING MQCONN. IF THE FIX IS PARTLY APPLIED, NO CONNECTIONS.

Obtain the fix for this APAR.

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
  .
  **NOTE**
  If this fix is partially applied, symptoms night include:
  - MQRC_HOST_NOT_AVAILABLE 2538 for any client trying to connect
  - Sender (SDR or CLUSSDR) channels trying to connect to the
    queue manager hang with a STATUS of BINDING and a substate of
    NETCONNECT.  A z/OS channel eventually times out with
      CSQX202E CSQXRCTL Connection or remote listener unavailable,
      channel <channel-name> connection <ipaddr>
      TRPTYPE=TCP RC=00000467 (ETIMEDOUT) reason=769E0291
    A similar message for distributed channels is AMQ9202.
  - The TSO command
      NETSTAT ALL (PORT nnnn)
    where "nnnn" is the MQ listener port number
    has MAXIMUMBACKLOG: 0000000000
  .
  Validate that the maintenance is correctly copied to the
  libraries used by the MSTR and CHIN jobs. In the libraries
  listed below, browse the load module and search for the CSECT
  names. The PTF eyecatcher must be UI64414 or higher for this
  fix to be applied correctly.
  - SCSQAUTH: Load module CSQILPLM: CSECT CSQIRECP
              Load module CSQMLPLM: CSECT CSQMSTRT
              Load module CSQXJST:  CSECT CSQXLMOD
  - SCSQMVR1: Load module CSQXRCTL: CSQXCCXT, CSQXCLIT
              Load module CSQXRCTL: CSQXCCXT
              Load module CSQXPIPI: CSQXBNT1, CSQXSFRE, CSQXSGET
  Another way to see the fix level for the first two SCSQAUTH
  modules is to issue the MQ command
    /cpf RECOVER QMGR(CSECT csect-name)
  where 'csect-name' is replaced with CSQIRECP and CSQMSTRT.
  The command does not work for the CSQXxxxx CSECTs.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of IBM MQ for z/OS Version 9       *
  *                 Release 1 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 2358
  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 is sysrouted FROM one or more of the following:

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

  UI64414 PH22382

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

• R100 PSY UI64414

     UP19/09/25 P F909

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.