Modes Of SQL Server Database Replication
Most medium and big businesses over the net are spread over different locations in distributed environments. They have different servers that cater to the different locations. In this scenario, SQL server database replication is a facility that allows database administrators to distribute data to various servers throughout an organization.
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Now what are the reasons you would want the facility of SQL Server replication for and what business needs would be satisfied by this facility? Well there are many such reasons. They are described below.
Offline processing- Replication even allows you to manipulate data in a purely offline mode if that is what you wish for machines not connected to your business network.Load balancing- The basic advantage of replication allows you to distribute the query load equally among all your servers. This is done by disseminating data among all your servers.
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Data redundancy- Through replication, you get a fail-over database server that is ready to pick up the query processing load almost instantaneously.
There are two main components to any replication scenario. First of all, publishers can offer data to other servers and more than one publisher can do so in any replication scheme. Secondly, subscribers, which are database servers that want to receive updates from publishers, whenever the data is modified. Nothing really prevents a single system from acting as a publisher as well as a subscriber. This advantage is mostly available in large-scale distributed environments.
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Microsoft SQL Server supports three types of database replication. These are described below.
Snapshot replication- A publisher simply takes a snapshot of the entire replicated database at an instant and shares it with the subscribers. Since this is both a resource and time intensive process, database administrators do not use it commonly for databases that change recurrently. In other words, this type of replication is used only rarely changing databases. It is also used to establish a baseline for future updates of databases (that may be in the pipeline) through merger or transactional replication.
Transactional replication offers a more viable solution for frequently changing databases. In this replication the transactional replication agent monitors the publisher in respect of changes made to the database and transmits the changes to subscribers. Such transmissions may occur immediately in synchronization with the changes or at set intervals.
Merge replication- With this type of replication, both the publisher and the subscriber is allowed to make changes to the database. During this time both of them work without an active network connection.
The merge replication agent monitors the changes made by both as soon as they reconnect to the network and modifies both databases accordingly. Conflicts in changes are resolved by use of a pre-defined conflict resolution algorithm. Merge replication is suitable for laptop users and for others who are not constantly connected to publishers.
SQL Server database replication capabilities depend entirely on the edition of the software application that you have. It provides nevertheless a powerful data mapping facility to you.