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Distributed Database Services

SQL Server has the ability to refer to the tables from multiple databases in a query, even the tables on a different computer. The tables are stated in the FROM clause of a SELECT statement, INSERT, UPDATE, or DELETE.

Distributed Queries, very useful. For example you will combine data from tabeltabel on several servers. Besides the remote table can also be accessed using OLE DB or ODBC.

SQL Server supports the use of Microsoft Distributed Transaction Coordinator (MS DTC) to conduct transactions in multiple SQL Server by using two-phase commit protocol. SQL Server can create a list of all remote servers automatically within a two-phase commit.

SQL Server also supports a number of model replication using replication architecture-and publish-subscribe. Replication automates the process to synchronize data between multiple SQL Server databases to facilitate the development of distributed applications.

Snapshot Replication is a replication of the basic model in SQL Server. With this model, a 'shot' with a scheduled publication created and distributed to all subscribers. This method is very useful if the information in the publication of the relatively static and subscriber only needs to refresh periodically.

Transactional Replication is used when all active subscriber on a LAN or WAN, and changes to the published data should be replicated to the installation of SQL Server subscriber.

Merge Replication is used if the subscriber is autonomous and often operate in a way disconnected. For example a user at the computer not connected can make changes in his data on the subscript when offline. When the user is connected to the network and start the synchronization, the subscript will be merged line by line with published data on the server. Just new rows and changes rows involved process.

Therefore, the publication can be simultaneously on multiple subscriber is offline. Conflict will easily occur when a user makes changes to the same data. Merge Replication supports a number of conflict resolution scheme that detects conflicts at the row or column level.

Microsoft Data Transformation Services (DTS) is a facility for the transformation and integration of data transfer. DTS is a COM object model for transferring data between a source and destination data. DTS object model will run the DTS package. A DTS package is a set of transformation commands and transfer data can be stored in a file in the system database msdb, or in Microsoft Repository.


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