What happens if one of the sites is unavailable?
In an asynchronous (store-and-forward) replication environment, local updates are stored in a deferred transaction queue until the remote site becomes available. When the remote site comes back up, these transactions are propagated and applied at the remote site in the order that they were originally applied at the local site. You can continue to make updates at any remaining replication sites. In addition to replicating the objects that you specify as part of your replication group, Oracle also replicates the replication catalog to each site. The replication catalog is a set of tables that determine which objects are being replicated, where they are being replicated, how often their changes are propagated, and so on. Replicating the replication catalog ensures that there is no single point of failure in a replicated environment.
