When and How?

Once you have determined why and what you are replicating and to which sites, you want to look at when the data needs to be delivered to each site and how to keep the data synchronized between all the distributed sites. This will help you determine your propagation schedule and method. We have already explained what Propagation means in Chapter 1, All the Pieces: The Parts of an Oracle 11g Streams Environment. Now, let's dig a bit deeper and look at how Propagation and data synchronization interrelate.

Data Propagation is one aspect of data synchronization; conflict detection and resolution are the other two aspects.

The two methods of data Propagation are Synchronous and Asynchronous.

Synchronous propagation is a distributed transaction in its truest form. All sites have to "agree" to commit the change before it can be committed anywhere; including the originating site. This means that all sites take out a lock on the piece of data until the transaction is committed at all...