Starting mirroring

CDC Replication provides two types of mirroring for source tables that are mapped to target tables: Continuous and Scheduled End (Net Change).

The type of mirroring you select depends on your business needs.

For both types of mirroring, before Management Console starts mirroring, it provides the following warnings:
  • The number of tables that will be refreshed before mirroring. This is informational.
  • The number of parked tables that will not be mirrored. This is informational.
  • Whether source tables are not mapped. This indicates incomplete mapping. CDC Replication cannot start subscriptions that are not completely mapped. Ensure that all tables that you want to mirror are properly mapped.

Continuous mirroring replicates changes to the target on a continuous basis. Use this type of mirroring when business requirements dictate that you need replication to be running continuously and you do not have a clearly defined reason to end replication at the present time.

Continuous mirroring is appropriate when your business processes require the source and target to be synchronized at all times. Continuous mirroring is also useful if your environment experiences frequent changes to large volumes of data. Instead of capturing these changes using a batch transfer, you can replicate changes to the target on a continuous basis.

Scheduled End (Net Change) mirroring replicates changes (to the target) up to a user-specified point in the source database log and then ends replication. Use this type of mirroring when business requirements dictate that you only replicate your data periodically and you have a clearly defined end point for the state of your target database when replication ends. Scheduled End (Net Change) mirroring allows you to end replication at the following points in your source database log:

  • Current time or “Now”
  • User-specified date and time
  • User-specified log position

These user specified end points ensure that your target database is in a known state when replication ends.

For example, if you start Scheduled End (Net Change) mirroring and specify a time of 12 PM, CDC Replication will continue mirroring all changes that have been committed to the target until 12 PM in the source database log. At this point, mirroring will end. You can also reschedule the Scheduled End (Net Change) mirroring to a new time or log position if business reasons warrant.