Avoiding
direct system dependencies can help to avoid ???cascading??? failures, allowing interconnected
systems to continue to operate even if one system fails. For example,
Streams can enable change data capture among Oracle databases and can be
used with non-Oracle databases by leveraging gateways. These capabilities are
described in more detail in the following section and in Chapter 13.
Oracle Streams Replication
You can use Oracle??™s built-in replication functionality to provide data redundancy.
Changes made by transactions are replicated synchronously or asynchronously to
other databases. If the primary database fails, the data is available from the other
databases. As of Oracle9i Release 2, log-based replication is included as part of
Streams. Replication is described in more detail in Chapter 13.
Real Application Clusters
Real Application Clusters can increase the scalability of the Oracle database over
multiple nodes in a cluster. But by supporting multiple instances with full access
to the same database, RAC also provides the highest levels of availability for protection
from the failure of a node in a clustered environment.
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