Request functions

Use a request function to deliver a replicated stored procedure from a primary database to the replicate database through the original user, the same user who invokes the stored procedure at the primary database. This type of function replication is usually used to enable the remote site to make changes to the central data with the authorized user. For example, a client application at a remote location needs to make changes to the central data. The client application first executes a stored procedure at the remote site—a procedure that may or may not make changes at the remote database. When the stored procedure executes, the replicate Replication Server passes a request function to the central site, where a corresponding stored procedure is invoked that updates the central data. In this example, the remote database is the primary database, while the central database is the replicate database of this request function.

With the primary copy model, a single central database contains all the latest updates. A client application at a remote site can update the central data using request functions. As updates occur at the central table, Replication Server captures the updates and sends them to replicate data servers through applied functions. Execution of stored procedures are stored in the Replication Server stable queues until they can be delivered to the appropriate databases.

To use a request function, create a stored procedure in the remote database and a corresponding stored procedure in the central database. Then, create a request function replication definition at the Replication Server that controls the remote database. The Replication Server that controls the central database can subscribe to this request function replication definition.When the stored procedure in the remote database is invoked, it invokes the stored procedure in the central database.

The Replication Server that manages the central database executes the stored procedure in the central database as the user who executed the stored procedure in the remote database. This guarantees that only authorized users can change central data.

In an application, Replication Server may replicate some or all of the data that is changed in the central database. The changes are distributed to the remote databases managed by Replication Servers that have subscriptions to table replication definitions or as separate applied functions. Either way, the effect of a transaction arrives at the central and then remote databases.

When you use request functions, all updates are made at the central database. This preserves Replication Server primary copy data model and protects the replication system from network failure and excess traffic.