The Sync Pull Notify feature decreases the delay between updating information about the master database and updating information on the replica databases. However, in some situations it might increase network traffic.
Sync Pull Notify might increase the load on your network. If your current synchronization approach is to synchronize each replica database every hour, and if you typically have multiple updates per hour, then you use only one set of network messages per replica database per hour to synchronize. If you switch to using the Sync Pull Notify feature, however, then you will have as many sets of network messages per replica database per hour as you have updates.
The converse is also true. If you currently refresh frequently but only have updates infrequently, then Sync Pull Notify might actually reduce your network traffic because you will only refresh when you actually need data; you will not need to "poll" to see if any data has changed. If you work in a situation where updates are infrequent, but it is necessary for you to know about those updates immediately when they occur, then Sync Pull Notify is a very good solution.
Note that "pull" and "push" (Sync Pull Notify) approaches are not mutually exclusive. You can use a combination of these approaches. As an example, you might choose to design your system so that, at a specific time every day, the master notifies the replicas that it is time to refresh. However, a repair person going out into the field and taking a replica database with them could also execute a REFRESH statement just before leaving the office, thus making sure that they have the most up-to-date data.
When designing your system for Sync Pull Notify, you might find it helpful to know that there are only three ways that data in the master database can be changed, and therefore there are only three situations in which you might need to "push" updated data to the affected replica databases:
1 Data might be changed directly on the master database, that is, a client might insert, update, or delete a record in a table on the master database.
2 The master database might receive data from a replica database.
3 If a database is both a master database and a replica database (for example, it is in a hierarchy that has three or more levels), then the database might request a refresh and receive data from its master database.