IT42355: MQ classes for JMS applications become blocked while creating a JMS Session when using automatic client reconnection

APAR status

• Closed as program error.

Error description

• A multi-threaded MQ classes for JMS application is configured to
  use a ConnectionFactory that contains information about how to
  connect to a queue manager using the CLIENT transport. The
  Connection Factory also has the following property set:
  
  CLIENTRECONNECTOPTIONS=QMGR
  
  which means that the MQ classes for JMS will use automatic
  client reconnection to try and reconnect to the queue manager if
  the application becomes disconnected for some reason.
  
  After the main thread within the application uses the Connection
  Factory to create a JMS Connection to the queue manager, other
  threads call the method:
  
  Connection.createSession(boolean, int)
  
  to create JMS Sessions which will be used to perform JMS
  operations with the queue manager.
  
  While one or more threads are calling this method, the queue
  manager fails over to another system. Intermittently, one or
  more threads that were creating a JMS Session at this time get
  stuck in the call to:
  
  Connection.createSession(boolean, int)
  
  and the number of channel instances (or TCP/IP connections)
  between the application and the queue manager start to grow.
  

Local fix

• Set the  -Dcom.ibm.mq.cfg.TCP.Connect_Timeout value to less
  than 60 seconds.
  

Problem summary

• ****************************************************************
  USERS AFFECTED:
  This issue affects users of:
  
  - The IBM MQ 9.2 classes for JMS.
  - The IBM MQ 9.3 classes for JMS.
  - The IBM MQ 9.3 classes for Jakarta Messaging.
  
  who have applications that use automatic client reconnection
  when connecting to a queue manager.
  
  
  Platforms affected:
  MultiPlatform
  
  ****************************************************************
  PROBLEM DESCRIPTION:
  When using either the MQ classes for JMS or the MQ classes for
  Jakarta Messaging:
  
  - Every JMS Connection created by an application has its own
  conversation or connection handle (hconn) to the queue manager.
  This is known as the "Parent hconn".
  - Each JMS Session created by an application also has its own
  conversation or hconn to the queue manager. Because JMS Sessions
  are created from JMS Connections, the Session's hconns are
  "Child hconns" of the Connection's "Parent hconn".
  
  Here is a simple diagram that shows this relationship
  
  JMS Connection               [Parent Hconn]
     |----> JMS Session 1      [    |----> Child Hconn1]
     |----> JMS Session 2      [    |----> Chilld Hconn2]
  
  If an application is connecting to a queue manager using the
  CLIENT transport, then the "Parent Hconn" and the "Child Hconns"
  will be assigned to a channel instance. The maximum number of
  hconns that can use a single channel instance is determined by
  the channel attribute SHARECNV (Shared Connections).
  
  
  Now, an MQ classes for JMS or MQ classes for Jakarta Messaging
  application will be able to use some functionality called
  "automatic client reconnection" if it is:
  
  - Either using a ConnectionFactory that has the
  CLIENTRECONNECTOPTIONS property set to either QMGR or ANY.
  - Or using a ConnectionFactory that has the
  CLIENTRECONNECTOPTIONS property set to ASDEF, and the MQ channel
  specified in the ConnectionFactory definition has the
  DefReconnect attribute set to QMGR or YES.
  
  When automatic client reconnection is being used, if the
  application become disconnected from the queue manager, the MQ
  classes for JMS or MQ classes for Jakarta Messaging will
  initially try to reconnect the Parent hconn associated with the
  JMS Connection. Once that hconn has been reconnected, the MQ
  classes for JMS will reconnect the Child hconns associated with
  the JMS Sessions created from the JMS Connection.
  
  If an application that was using this functionality:
  
  - Become disconnected from the queue manager while it was
  calling the method Connection.createSession(boolean,int)
  - And the attempt to reconnect the Parent hconn associated with
  the JMS Connection failed with a permanent error.
  
  then the MQ classes for JMS and MQ classes for Jakarta messaging
  would get stuck within the Connection.createSession(boolean,int)
  call, continually creating new hconns to the queue manager. This
  would result in the number of channel instances between the
  application and the queue manager growing over time.
  

Problem conclusion

• To resolve this issue, the MQ classes for JMS and MQ classes for
  Jakarta Messaging have been updated so that:
  
  - If an application becomes disconnected from a queue manager
  while calling the Connection.createSession(boolean,int) method.
  - And an attempt to automatically reconnect the the application
  fails with a permanent error.
  
  then the Connection.createSession(boolean,int) method will exit
  with a JMSException containing a linked exception which includes
  MQ reason code 2548 (MQRC_RECONNECT_FAILED).
  
  ---------------------------------------------------------------
  The fix is targeted for delivery in the following PTFs:
  
  Version    Maintenance Level
  v9.2 LTS   9.2.0.10
  v9.3 LTS   9.3.0.5
  v9.x CD    9.3.2
  
  The latest available maintenance can be obtained from
  'WebSphere MQ Recommended Fixes'
  http://www-1.ibm.com/support/docview.wss?rs=171&uid=swg27006037
  
  If the maintenance level is not yet available information on
  its planned availability can be found in 'WebSphere MQ
  Planned Maintenance Release Dates'
  http://www-1.ibm.com/support/docview.wss?rs=171&uid=swg27006309
  ---------------------------------------------------------------
  

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:

Fix information

• Fixed component name

  MQ BASE V9.2

• Fixed component ID

  5724H7281

Applicable component levels