Log-Based Data Capture

uses log-based data capture to gather data for replication. reads the logical log to obtain the row images for tables that participate in replication and then evaluates the row images.

Log-based data capture takes changes from the logical log and does not compete with transactions for access to production tables. Log-based data-capture systems operate as part of the normal database-logging process and thus add minimal overhead to the system.

Two other methods of data capture, which does not support, include:
  • Trigger-based data capture

    A trigger is code in the database that is associated with a piece of data. When the data changes, the trigger activates the replication process.

  • Trigger-based transaction capture

    A trigger is associated with a table. Data changes are grouped into transactions and a single transaction might trigger several replications if it modifies several tables. The trigger receives the whole transaction, but the procedure that captures the data runs as a part of the original transaction, thus slowing down the original transaction.