PH31012: CICS XID ENHANCEMENT

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• CICS XID enhancement
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: All.                                         *
  ****************************************************************
  * PROBLEM DESCRIPTION: Two DB2 threads from two CICS regions   *
  *                      involved in the same unit of work can   *
  *                      deadlock.                               *
  ****************************************************************
  DB2 does not know that two threads from two different CICS
  regions may be from the same uow in which case it should share
  locks and not lock one thread out whilst the other thread
  holds the lock.
  
  Keywords: AD2Z ASP3 abendAD2Z abendASP3
  

Problem conclusion

• The CICS-DB2 Attach will pass an XID to DB2. No changes are
  required from DB2, as it already supports passing an XID on
  signon from CICS-DB2 Attach. Two threads that pass the same
  XID will share locks and not deadlock.
  
  The passing of an XID will occur if feature toggle
  com.ibm.cics.db2.sharelocks is set to true.
  
  CICS-DB2 Attach will query MVS RRS to see if a unit of work was
  initiated from outside of CICS and being coordinated by MVS RRS.
  It will pass in the lu6.2 uowid as a filter and RRS will return
  the associated unit of recovery if there is one. If an RRS unit
  of recovery is returned, then CICS will obtain the XID
  associated with the RRS Unit of Recovery and pass the short
  form of it to DB2 (ie with no BQUAL).  This scenario is the case
  when the initial part of a distributed unit of work ran under
  IMS/TM, invoked DB2, and then invoked CICS via appc/LU6.2.
  
  If RRS is not involved in the unit of work, CICS will generate
  an XID based on data from the LU6.2 uowid associated with the
  unit of work. All CICS regions participating in the same unit of
  work will generate the same XID from the same lu6.2 uowid.
  
  Passing an XID to DB2 involves a partial signon to DB2 at the
  start of each unit of work. The number of partial signons for
  existing workloads will increase compared with previous
  releases.
  
  A signon at the start of each unit of work will close any held
  cursors. Therefore when using an XID, the ability for
  held cursors to remain open across syncpoints is not supported.
  A subsequent fetch for a previously held cursor will receive
  a -501 sqlcode.
  
  The CICS Knowledge Center will be updated to reflect the support
  for CICS passing an XID to DB2 and the use of the
  com.ibm.cics.db2.sharelocks feature toggle.
  

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:

  UI73629 UI73630

Modules/Macros

• DFHD2CC  DFHD2CM1 DFHD2CO  DFHD2D2  DFHD2DUF DFHD2EDF DFHD2EX1
  DFHD2EX2 DFHD2EX3 DFHD2IN1 DFHD2MSB DFHD2RL  DFHD2RP  DFHD2ST
  DFHD2STP DFHD2STR DFHD2TM  DFHD2TR1 DFHD2TRI DFHDSMT
  

Fix information

• Fixed component name

  CICS TS Z/OS V5

• Fixed component ID

  5655Y0400

Applicable component levels

• R200 PSY UI73630

     UP21/01/27 P F101

• R300 PSY UI73629

     UP21/01/27 P F101

Fix is available

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