How Transactional Replication Works

Transactional replication is implemented by the SQL Server Snapshot Agent, Log Reader Agent, and Distribution Agent. The Snapshot Agent prepares snapshot files containing schema and data of published tables and database objects, stores the files in the snapshot folder, and records synchronization jobs in the distribution database on the Distributor.
The Log Reader Agent monitors the transaction log of each database configured for transactional replication and copies the transactions marked for replication from the transaction log into the distribution database, which acts as a reliable store-and-forward queue. The Distribution Agent copies the initial snapshot files from the snapshot folder and the transactions held in the distribution database tables to Subscribers.
Incremental changes made at the Publisher flow to Subscribers according to the schedule of the Distribution Agent, which can run continuously for minimal latency, or at scheduled intervals. Because changes to the data must be made at the Publisher (when transactional replication is used without immediate updating or queued updating options), update conflicts are avoided. Ultimately, all Subscribers will achieve the same values as the Publisher. If immediate updating or queued updating options are used with transactional replication, updates can be made at the Subscriber, and with queued updating, conflicts might occur. For more information, see How Updatable Subscriptions Work.



URL: http://msdn.microsoft.com/en-us/library/ms151706(v=sql.105).aspx