Today, Oracle supports Sockets Direct Protocol (SDP)
and asynchronous I/O protocols, lighter-weight transports than those used in previous
traditional TCP/IP based RAC implementations. More recent database releases
further improved performance by leveraging faster interconnects such as Infiniband
networks through support of Reliable Datagram Sockets (RDS). For example, Infiniband
node-to-node latency is about a tenth of the latency in Gigabit Ethernet
(typically about 70-80 microseconds).
Prior to Real Application Clusters, you would configure clusters to deliver higher
throughput or greater availability for the system. In the high-availability scenario, if a
single node fails, a secondary node attached to the shared disk can get access to the
same data. Queries can run to completion without further intervention through
transparent client failover. RAC provides both availability and scalability since each
node in a cluster can act as a failover node for all the other nodes in the cluster.
Real Application Clusters are increasingly used in Windows and Linux environments
where a single platform cannot scale adequately or as an alternative to higher-cost
Unix high-end solutions.
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