DB2 Replication Guide and Reference

Specifying Tuning Parameters for the Capture Program

To control the performance of the Capture program, you can specify the following tuning parameters in the ASN.IBMSNAP_CCPPARMS tuning parameters table:

Retention limit

The number of minutes to keep the change data (CD) table rows and the unit-of-work (UOW) table rows. The default value is 10,800, which is 7 days. The rows are deleted up to where the changes have been applied.

Lag limit

The number of minutes the Capture program can be backlogged from the current local time before shutting itself down. The default value is 10,800 (which is 7 days). This value is higher for a busy system; therefore, a lower lag limit shuts down the Capture program.

Commit interval

The number of seconds to wait before issuing a COMMIT statement. The default value is 30 seconds. Set the interval smaller than the DB2 timeout interval if the Capture and Apply programs are running at the same time. This precaution helps to avoid locking overhead for Capture running on DB2 for MVS 3.1 where uncommitted read is not supported. If the Apply program is not running at the same time as the Capture program, you can set the commit interval no higher than the DB2 timeout interval.To avoid unnecessary lock contentions, issue a COMMIT statement regularly. This should be close to the DB2 timeout value since COMMIT has associated resource costs. See the DB2 Administration Guide for additional details.

Prune interval

The number of seconds to wait before pruning the staging tables. The default value is ten times the commit value or 300 seconds, whichever is larger. This parameter is ignored if you start the Capture program with the NOPRUNE option; however, you can override this option with the PRUNE command.

To specify the tuning parameters, do one of the following tasks:

• Modify DPCNTL.* in the Control Center /sqllib/samples/repl directory before you define the first replication source for a database.

• If you want to change the default values, update the table with the following SQL statement after you create the tuning parameters table:

  UPDATE TABLE ASN.IBMSNAP_CCPPARMS
  SET RETENTION_LIMIT=number_of_minutes,
  LAG_LIMIT=number_of_minutes,
  COMMIT_INTERVAL=number_of_seconds,
  PRUNE_INTERVAL=number_of_seconds
  

If you need to change the values and refresh the tuning parameters while the Capture program is running, enter the REINIT command after changing the table values.

For information on the structure of the tuning parameters table, see Chapter 19. Table Structures.

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