Replication Guide and Reference

Setting up the Capture program

This section describes setting the Capture program generally. See the appropriate chapter for your operating system environment (in Operations) for specific information about setting up the Capture program.

Specifying tuning parameters for the Capture program

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

Retention limit

The number of minutes to keep the CD table rows and the unit-of-work (UOW) table rows. The default value is 10 080, which is 7 days.

For AS/400, you can keep the size of tables smaller by reorganizing them using the RGZPFM command.

Lag limit

The number of minutes that the Capture program can be backlogged from the current local time before shutting itself down. The default value is 10 080, which is 7 days. If this value is exceeded, the Apply program will perform a full refresh of all target tables.

Recommendation: Set a high value for the lag limit to ensure the Capture program does not shut itself down unnecessarily.

If the database does not have or support an archive log, and the Capture program shuts itself down, you should perform a cold start of the Capture program.

Commit interval

The number of seconds that the Capture program waits before issuing a COMMIT statement. The default value is 30 seconds.

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.

For AS/400, this value has a different meaning: it is the number of seconds between the time that an application program updates a source table and the time that the corresponding update in the CD table is written to disk. The commit interval can range from 30 to 600 seconds, and the default is 180. If the value is too small, overall system performance can be degraded.

Prune interval

The number of seconds that the Capture program waits 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 by using the prune command.

For AS/400, you can override this value by specifying a value for the wait-time subparameter of the CLNUPITV keyword of the STRDPRCAP command. If you specify *NO on the start-clean-up subparameter of the CLNUPITV keyword, the prune interval value is completely ignored.

For AS/400, if you start up the Capture program daily, *NO allows you to defer pruning (for example, to the weekend). During the week, you can use CLNUPITV (*DPRVSN *NO) on the STDPRCAP command. On weekends, you can use CLNUPITV (*DPRVSN *IMMED), which is the default.

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

• Customize the DPCNTL.* file in the DB2 \sqllib\samples\repl directory before you define the first replication source for a database. ¹⁵

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

  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 AS/400, enter the INZDPRCAP command; for more information about the INZDPRCAP command, see Reinitializing Capture for AS/400.

  For information on the structure of the tuning parameters table, see Table structures.

• Run the AS/400 CHGDPRCAPA command. See Changing Capture program attributes for more information about this command.

Restrictions when running the Capture program

The following actions cause the Capture program to terminate while it is running. Stop the Capture program if you want to perform any of the following tasks:

• Remove an existing replication source table. If you remove an existing replication source, the Capture program might attempt to insert data into a CD table that no longer exists.

• Make changes (other than ALTER ADD changes) that affect the structure of source tables or CD tables. This includes changes resulting from data definition language or utilities. Structural changes can compromise the data integrity of the copies.

Other Capture program restrictions include:

• If the Capture program shuts itself down, perform a cold start if the database does not have or support an archive log.

• Source tables must be created or altered using the DATA CAPTURE CHANGES option. The DB2 Control Center and DJRA automatically specify these keywords when you define replication sources.

• Capture does not capture any changes made by DB2 utilities, even if you specify LOG=YES.

¹⁵

Customizing DPCNTL.400 is not necessary if you already installed DataPropagator Relational for AS/400.

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