GAPFIX (Fix CDC Gaps) › When to Use

When to Use

Use the GAPFIX function when a gap occurs during Change Data Capture (CDC) processing.

A gap can occur at the following three points in time:

• The first gap can occur when a MUF is defined to have CDC set for a set of databases, but the MUF is then enabled and runs for an extended period of time without an established or started Change Data Capture Listener (CDCL) task, during which time the LXX spills its first CDC record. The CDCL task fails to see the spilled data when it is established or started after the spill, because the spilled data is then missing from the LXX. This point in time includes cases in which the CDC database was for some reason null loaded.
• The second gap can occur when the source MUF and the CDCL task are running normally, the CDC database becomes full, and time passes before the full database is noticed and resolved. By the time the full database is resolved, the LXX no longer has enough room available for the work that occurred before the resolution took place, resulting in some of the CDC data being spilled and overlaid on the LXX. When the CDCL task is restarted, the gap is detected.
• The third gap can occur when the CDCL task starts and processes prior CDC records (the prior records are known to the associated control record) but then discovers that while it was stopped the LXX was initialized or reset. This situation indicates that data could have existed while the CDCL task was stopped but before the LXX was initialized or reset. In this case, provide that missing data before you start new CDC records.

You handle each of the three previously described cases based on whether the control record still exists.

• If the control record still exists, execute the GAPFIX function of DBUTLTY with the ordered RXX file or files from the date-time of the gap. The date-time of the gap is provided in message DB03121I. GAPFIX directs message DB03121I to the MUF JES log. The STARTED and ENDED examples of message DB03121I are:

  DB03121I - DBCPGPR DBDVL A-DBDVM01 STARTED LASTLXX-00000000000000
  
  DB03121I - DBCPGPR DBDVL A-DBDVM01 ENDED LASTLXX-20060622142058
  

  The date-time of the gap is provided in the ENDED form of message DB03121I following the LASTLXX in the format of ccyymmddhhmmss..

  • cc is the century
  • yy is the year
  • mm is the month
  • dd is the day
  • hhmmss to give the hour and minutes and seconds.

  For more information about message DB03121I, see the CA Datacom/DB Message Reference Guide.

  Note: GAPFIX also can generate error message DB03122E and informational message DB03123I.

  For more information about messages DB03122E and DB03123I, see the CA Datacom/DB Message Reference Guide. Examples are:

  DB03122E - DBCPGPR ERROR RXX EMPTY
  
  DB03123I - DBCPGPR ENDING
  

  The GAPFIX function reads the control record and processes the RXX data in the same way that the CDCL task processes the LXX directly. The GAPFIX function adds TSN records and adds or deletes MNT records, just as CDCL does. It also updates the control record and does commits, similar to CDCL, but because the RXX is not track-oriented, the commits occur either after every 1000 CDC records or 10000 log records. The GAPFIX function of DBUTLTY can always be restarted if for some reason it fails.

• If the control record existed and you provided the starting date and time, if a commit has occurred a control record now exists and the date and time option must be removed when running the GAPFIX function. All RXX data needs to be processed, or at least all not currently on the LXX. If the CDCL task is set to open, the last log record handled by the GAPFIX function remains on the LXX and can therefore restart with no risk of missing data. Data spilled to the LXX still exists on the LXX until it has been overlaid with new data.

  If the control record does not exist, it might be because CDC is just starting or because the CDC database has been lost. If a control record does not exist, use GAPFIX and begin by choosing a starting date and time to use as the value of the GAPFIX DATETIME= keyword (see How to Use). In executing the GAPFIX function, ensure that the first and all subsequent RXX files after the date and time you specify are included. When GAPFIX execution begins, it makes certain that no control record exists then adds a record with a starting date and time of the first log record that matches or comes after the DATETIME= you specified. GAPFIX processes all RXX data in the same way as CDCL would. At completion, the CDC control record is updated to reflect the last RXX log record. After the GAPFIX function completes, you have two choices as follows:

  • You can run GAPFIX again, providing the last RXX file and newer RXX files, if any exist.
  • Alternately, you can direct the CDCL task to open with CDCL_OPEN, causing the CDCL task to open and read the control record. If the oldest log record processed is now on the LXX, the CDCL task continues with normal processing. If the LXX does not have the needed record, it indicates that a new gap has been found. The CDCL task issues a new gap message, and closes.