Task 16: Replication

                                                   Replication

Replication is the mechanism for creating and maintaining multiple copies of the same data. Replication allows:
• Multiple copies of data can be kept in sync. Load balancing. Replication allows you to disseminate your data to a number of servers and then distribute the query load among those servers.
• Allows data be closer to users, improving performance. Redundancy. Replication allows you to build a fail-over database server that’s ready to pick up the processing load at a moment’s notice.
• Allows a branch office to work when not connected to the main office. Offline processing. You may wish to manipulate data from your database on a machine that is not always connected to the network.
• Separate process and offload work from production servers

What are the Components of Replication

Following are the important components in replication setup
• A publication contains articles.
• The publisher either distributes the magazine directly or uses a distributor.
• Subscribers receive publications to which they have subscribed.

What are the Server Roles Involved in Replication ?

SQL Servers can be assigned three different roles in a replication topology:
• Publishers create and modify data. Publishers have data to offer to other servers. Any given replication scheme may have one or more publishers.
• Distributors store replication-specific data associated with one or more publishers.
• A subscriber holds a replica copy of the data. Subscribers are database servers that wish to receive updates from the Publisher when data is modified.

What are the type of replication available in SQL Server ?

SQL Server supports

Snapshot replication sends the entire data set to the subscriber. The publisher simply takes a snapshot of the entire replicated database and shares it with the subscribers. You don't use this replication type for databases that change frequently. 
Transactional replication only sends modifications to the data. The replication agent monitors the publisher for changes to the database and transmits those changes to the subscribers.
Merge replication items are modified at both the publisher and subscribers. Allows the publisher and subscriber to independently make changes to the database. Both entities can work without an active network connection. When they are reconnected, the merge replication agent checks for changes on both sets of data and modifies each database accordingly.

Here you can find how to configure the data replication in SQL Server 2008

You may wish to implement replication in your organization for a number of reasons, such as:

• Load balancing. Replication allows you to disseminate your data to a number of servers and then distribute the query load among those servers.
• Offline processing. You may wish to manipulate data from your database on a machine that is not always connected to the network.
• Redundancy. Replication allows you to build a fail-over database server that’s ready to pick up the processing load at a moment’s notice.