PK85641: ENQ CONTENTION ON DB2 ARCHIVE LOG

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• ENQ contention can occur for a DB2 archive tape after DB2 uses
  the tape and is waiting for the deallocation time to expire.
  .
  When DB2 needs a tape device for read of an archive tape, and
  the maximum count specified in the zparm DSN6LOGP MAXRTU field
  hs been reached, DB2 can reuse a drive that is waiting for the
  time interval DEALLCT to expire.
  .
  This condition does not occur if the time interval DEALLCT is
  set to zero.
  GRS contention report will show the allocation.
  DB2 -display archive command will not show the tape volume.
  

Local fix

• Set DSN6LOGP DEALLCT to zero in zparm.
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of DB2 with archive log data       *
  *                 sets on tape volumes.                        *
  ****************************************************************
  * PROBLEM DESCRIPTION: An ENQ on SYSZVOLS for an archive log   *
  *                      data set tape volume can be left        *
  *                      allocated to the DB2_MSTR address       *
  *                      space after the archive log data set    *
  *                      has been closed and deallocated.        *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  If DB2 reaches the maximum tape unit count allocated for
  archive read processing (DSN6LOGP MAXRTU parm in DSNZPARM),
  DSNJR206 will look for allocated tape volumes that are in
  the delayed deallocation process (DSN6LOGP DEALLCT parm in
  DSNZPARM).  If any tape volumes are in delayed deallocation,
  DB2 will 'steal' the tape unit by modifying the JFCB with the
  new archive log data set information and issuing an OPEN-J
  for this archive log.  The original archive volume will be
  closed and unloaded, allowing the new archive log volume
  to be opened on the allocated tape unit.  Even though the
  tape volume has been unloaded, the ENQ on SYSZVOLS for the
  archive log tape volume is not released, apparently because
  DB2 runs authorized.
  

Problem conclusion

• DB2 will now mark an archive log data set in delayed
  deallocation as 'expired', so it will be deallocated
  when DB2 has reached the maximum archive tape unit count.  This
  will allow the new archive log tape read request to be honored
  after the 'expired' archive log tape unit has been
  deallocated.
  Recommendation:  Only use the delayed deallocation option
  when you know there will be multiple requests for the same
  archive log tape volume.  Data sharing users may not want to
  use this option as it can cause requests from other members
  of the group to wait for the archive log volume while in
  delayed deallocation.  Also, make sure that the maximum
  archive tape unit count is sufficiently large to prevent
  unnecessary queuing for tape units.  Both options can be
  modified with the -SET ARCHIVE command for this instance of
  DB2.  The values in DSNZPARM will be used when DB2 is
  restarted.
  

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:

  UK46655 UK46656

Modules/Macros

• DSNJR206 DSNJR208
  

Fix information

• Fixed component name

  DB2 OS/390 & Z/

• Fixed component ID

  5740XYR00

Applicable component levels

• R810 PSY UK46655

     UP09/05/30 P F905

• R910 PSY UK46656

     UP09/05/30 P F905

Fix is available

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