PI94872: Update operations that overlap an external load might not be mirrored correctly

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• If a table is being actively changed with update operations
  while it is being externally refreshed, an edge condition could
  occur that causes subsequent update records for that table to
  be mirrored incorrectly. Specifically, if the update is an
  out-of-place update, for example caused by a change in a
  partition or an increase in size, and the start of the external
  load is logged between the separate log records for the before
  and after images, then subsequent updates could be mirrored by
  using the before image of one update and the after image of
  another. Possible consequences could be lost data on the target
  if the earlier update used a key that is different than the
  later update. In this situation, the mirrored key change would
  have the net effect of deleting the record on the target based
  on the prior update.
  

Local fix

• Re-do the external load ensuring that the table does not have
  in-flight updates at the time the start of the external load.
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: Users of InfoSphere Change Data Capture for  *
  *                 z/OS.                                        *
  ****************************************************************
  * PROBLEM DESCRIPTION: If a table is being actively changed    *
  *                      with update operations while it is      *
  *                      being externally refreshed, an edge     *
  *                      condition could occur that causes       *
  *                      subsequent update records for that      *
  *                      table to be mirrored incorrectly.       *
  *                                                              *
  *                      Specifically, if the update is an       *
  *                      out-of-place update, for example        *
  *                      caused by a change in a partition or    *
  *                      an increase in size, and the start of   *
  *                      the external load is logged between     *
  *                      the separate log records for the        *
  *                      before and after images, then           *
  *                      subsequent updates could be mirrored    *
  *                      by using the before image of one        *
  *                      update and the after image of another.  *
  *                                                              *
  *                      Possible consequences could be lost     *
  *                      data on the target if the earlier       *
  *                      update used a key that is different     *
  *                      than the later update. In this          *
  *                      situation, the mirrored key change      *
  *                      would have the net effect of deleting   *
  *                      the record on the target based on the   *
  *                      prior update.                           *
  ****************************************************************
  * RECOMMENDATION: APPLY CORRECTIVE SERVICE                     *
  ****************************************************************
  The code that constructs update operations from their
  corresponding log records incorrectly associated the second log
  record of the split update with the first log record of the
  next update for that table. Because the split update cannot be
  reconstructed due to the usage pattern of the external load, it
  should be discarded. This process allows following updates to
  be processed normally.
  

Problem conclusion

• The code that constructs update operations from their
  corresponding log records was modified to discard the split
  update.
  

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:

  UI54988

Modules/Macros

•    CHCDLSGP
  

Fix information

• Fixed component name

  INFO SRVR CDC Z

• Fixed component ID

  5655U7600

Applicable component levels

• RA21 PSY UI54988

     UP18/04/07 P F804

Fix is available

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