Enterprise Replication uses log-based data capture to gather data for replication. Enterprise 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 Enterprise Replication does not support, include:
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.
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.