Progress® DataXtend™ Remote Edition and Microsoft® SQL Server™ both provide a set of replication tools for copying, distributing, and synchronizing data from one database to another. DataXtend RE (Remote Edition) provides the most comprehensive and flexible replication and synchronization tools available for software developers and enterprise IT departments to make their applications mobile and available both on-line and off-line. While SQL Server replication technology can be used for replicating data for reporting, backup and recovery, or mobile applications, its features are better suited for non-mobile, non-distributed/connected applications.

If you are considering Microsoft replication for a mobile or distributed application, this whitepaper will help you understand which features may and may not be appropriate before investing valuable development resources.

There are three types of replication available with Microsoft SQL Server. These are snapshot replication, transactional replication and merge replication. Each replication type provides different capabilities depending on the application, and different levels of ACID properties of transactions and site autonomy. Snapshot replication is the process of copying and distributing data exactly as it appears at a moment in time. This may be helpful in situations where data is rather static or infrequently changes. With transactional replication, an initial snapshot of data is propagated to Subscribers, and then when data modifications are made at the Publisher, the individual transactions are captured and propagated to Subscribers. This would be useful in applications where changes must be replicated quickly to subscribers, but may require a nearly constant network connection for installations where a high rate of change persists and/or limited disk resources exist.

With merge replication, an initial snapshot is applied to the distributed sites; subsequent changes to the database are tracked, then published to all subscribers. This allows the replicated sites to work online or offline and merge data modifications made at multiple sites into a single, uniform result at a later time. Merge replication synchronizes pairs of sites to the same data values. As in any distributed environment, as other sites may be simultaneously changing, ACID properties cannot be assured. Data values in the replication topology converge to the same value over time..

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