During the installation of a RAC, you can configure the Enterprise Manager agent and Enterprise
Manager Database Control to manage your cluster. EM Database Control extends the functionality
available to manage a single instance by providing a cluster-aware layer; you can manage both
the Oracle instances and the underlying cluster configuration from a single web interface.
In subsequent chapters, we will present other ways to ensure high database availability and
recoverability: Chapter 13 will give a detailed look at Oracle Data Guard for near-real-time
failover capabilities, and Chapter 17 will cover Oracle Streams for advanced replication. In
Chapter 14, we??™ll finish up our discussion on Flashback options started in Chapter 7 by showing
you how to perform Flashback Drop and Flashback Database as well as how to use LogMiner to
undo individual transactions.
Overview of Real Application Clusters
A Real Application Cluster is highly available and scalable. The failure of one node in the cluster
does not affect client sessions or the availability of the cluster itself until the last node in the
cluster fails; the only impact a lost node has on the cluster is a slight degradation in response
time, depending on the total number of nodes in the cluster.
A RAC database has a few disadvantages. Licensing costs are higher, because each node in
the cluster has to have its own Oracle license. The close physical proximity of the nodes in the
cluster due to the high-speed requirements of the cluster interconnect means that a natural disaster
can take out the entire cluster; using a remote standby database can help alleviate some of these
concerns.
Pages:
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566