Types of Replication

* Snapshot Replication
Snapshot replication is the simplest replication type.
With snapshot replication, a picture, or snapshot,
of the database is taken periodically and propagated to subscribers.
The main advantage of snapshot replication is
that it does not involve continuous overhead on publishers and subscribers.
That is, it does not require publishers to continuously monitor data changes,
and it doesn't require the continuous transmission of data to subscribers.
The main disadvantage is that the database on a subscriber is only as current as the last snapshot.


In many cases, snapshot replication is sufficient and appropriate
- for example, when source data is modified only occasionally.
Information such as phone lists, price lists,
and item descriptions can easily be handled by using snapshot replication.
These lists can be updated once per day during off hours.


* Transactional Replication
Transactional replication can be used to replicate changes to the database.
With transactional replication, any changes made to articles (a set of data configured for replication)
are immediately captured from the transaction log and propagated to the distributors.

Using transactional replication, you can keep a publisher
and its subscribers in almost exactly the same state,
depending on how you configure the replication.
Transactional replication should be used
when it is important to keep all of the replicated systems current.
Transactional replication uses more system overhead than snapshot replication
because it individually applies each transaction that changes data in the system
to the replicated systems.
However, transactional replication keeps the systems in a more up-to-date state
than do snapshot and merge replication.


* Merge Replication
Merge replication is similar to transactional replication
in that it keeps track of the changes made to articles.
However, instead of individually propagating transactions that make changes,
merge replication periodically transmits a batch of changes.
Because merge replication transmits data in batches, it is also similar to snapshot replication.
(Although with snapshot replication, all data configured for replication,
not just changes, is propagated.)


Source: Microsoft SQL Server 2000 Administrator's Companion Book