PH65656: CORRECT EAV RELATIVE BLOCK NUMBER CALCULATION TO ACCOUNT FOR BLOCK NUMBER WRAP AND ENHANCE OLDS OVERWRITE 25/03/14 PTF PECHANGE

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• Correct EAV relative block number calculation to account for
  block number wrap and enhance OLDS overwrite detection
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: Classic CDC for z/OS for IMS                 *
  *                 IIDR for IMS                                 *
  ****************************************************************
  * PROBLEM DESCRIPTION: Correct EAV relative block number       *
  *                      calculation to account for block        *
  *                      number wrap and enhance OLDS overwrite  *
  *                      detection                               *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  The IMS log reader reports a non-recoverable error that forces
  replication to stop for all subscriptions when reading an
  active OLDS and the block count wraps. The OLDS must be an
  extended address volume dataset (for example, a striped
  dataset).
  The error is reported when the IMS log reader is waiting for
  IMS to write more data to the log after the block count has
  wrapped and IMS has switched to the next OLDS.
  This APAR also addresses another problem where the IMS log
  reader is unable to detect that IMS has overwritten an OLDS
  with new log data. Typically, a log overwrite is detected
  because the block number in the new data written by IMS is
  larger than the block number of the first block in the log plus
  the block capacity of the OLDS being read. However, if a
  sequence of log switches is performed causing little data to be
  written in the OLDS, the new block number may be much smaller.
  If this happens, the IMS log reader will not detect the
  over-write until IMS overwrites the log a second time.
  

Problem conclusion

• The OLDS relative block calculation has been updated to
  correctly position in an OLDS stored on an extended address
  volume when the block number wraps in that OLDS.
  The overwrite detection logic has been enhanced to handle the
  case where frequent log switches were performed by checking
  DBRC to determine if IMS has overwritten the OLDS that the IMS
  log reader is currently reading. The DBRC check occurs when a
  new block of data is read, and the block number is not one more
  than the previously read block of data (the block number is
  incremented by one for each new block written to the log).
  The call to check DBRC is only performed when the difference
  between the new block number and the previous block number
  exceeds a threshold. It is possible for the IMS log reader to
  skip over one or two new blocks of data, so the default
  threshold is 7. The default threshold can be modified, and the
  calls to DBRC can be disabled by updating the TASKPARM global
  configuration parameter to include a BLOCKLIMIT setting.
  Setting BLOCKLIMIT=0 disables calling DBRC to check for one of
  these special overwrite conditions. Specifying a non-zero value
  identifies the read ahead limit before DBRC is called to check
  to see if it has overwritten the OLDS currently being read.
  Using the BLOCKLIMT keyword to override default processing is
  not expected to be necessary. If it is, updates to the
  BLOCKLIMT setting take effect the next time the IMS log reader
  reads ahead.
  

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:

  UO02474

Modules/Macros

•    CECCLRFU CECCLRIC CECCLRID CECCLRIE CECCLRIH
  CECCLRII CECCLRIM CECCLRIQ CECCLRIR CECCLRIS CECCLRIT CECCSRVC
  

Fix information

• Fixed component name

  CLASSIC FED & E

• Fixed component ID

  5697I8200

Applicable component levels

• RB30 PSY UO02474

     UP25/03/18 P F503 Ø

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.