Checking the values of IBM InfoSphere Change Data Capture system parameters

Verify that InfoSphere® CDC system parameters are set to appropriate values so that query plans can use shadow tables

To ensure that the required InfoSphere CDC system parameters are set correctly:

1. Log in to the cdc-server-host as a cdc-user.
2. Change to the bin folder for InfoSphere CDC for DB2® for LUW by issuing the following command:

   $ cd /cdc-installation-dir/bin 

3. View the current settings for the system parameters that are not set to their default values by issuing the dmset command as follows:

   ./dmset -I cdc-instance-name

4. Check whether the value of the acceptable_latency_in_seconds_for_column_organized_tables system parameter was modified by issuing the dmset command as follows:

   ./dmset -I cdc-instance-name
       acceptable_latency_in_seconds_for_column_organized_tables

   The default setting for the acceptable_latency_in_seconds_for_column_organized_tables system parameter is 5 seconds.

   The acceptable_latency_in_seconds_for_column_organized_tables system parameter controls the interval between batched commits when InfoSphere CDC replication is active. The value of the acceptable_latency_in_seconds_for_column_organized_tables system parameter must be less than the value of the CURRENT REFRESH AGE special register. If the interval between batched commits is similar to or larger than the value of the CURRENT REFRESH AGE special register, latency might regularly become out-of-date for short periods. When latency becomes out-of-date, queries are routed to base tables intermittently.

5. Ensure that the maintain_replication_mqt_latency_table system parameter is set by issuing the dmset command as follows:

   ./dmset -I maintain_replication_mqt_latency_table

   For InfoSphere CDC to update the SYSTOOLS.REPL_MQT_LATENCY table, you must set the maintain_replication_mqt_latency_table system parameter. By default, this parameter is set to false, and InfoSphere CDC does not send latency information to DB2. In the absence of latency information that is required to make routing decisions, shadow tables are not used.

6. Ensure that the mirror_auto_restart_interval_minutes system parameter is set to a value greater than 0 by issuing the dmset command as follows:

   ./dmset -I mirror_auto_restart_interval_minutes

   The mirror_auto_restart_interval_minutes system parameter determines the interval in minutes between attempts to restart a persistent subscription when replication for that subscription fails due to a recoverable error. A value of 1 or 2 seconds is suitable for most environments.