With Real Application Clusters, the problem caused by pings was eliminated. RAC
fully supports the technology known as Cache Fusion. Cache Fusion makes all the
data in every cache on every machine in a Real Application Cluster available to every
other machine in the cluster. If one machine needs a block that is either being used
by another machine or simply residing in the cache of another machine, the block is
directly shipped to the requesting machine, usually over a very high-speed
interconnect.
Figure 9-6. RAC architecture
Disk 1 Disk 2
Node 1 Node 2 Node 3 Node 4
High Availability | 217
Cache Fusion means that you do not have to work around the problems of pinging.
With Real Application Clusters you will be able to see significant scalability improvements
for most all applications, without any modifications. With that said, for OLTP
applications deployed to RAC (where there are frequent modifications to indexes
within a small set of leaf blocks), reverse key indexes might be used to distribute
inserts across leaf keys in the index and eliminate possible performance issues for
this special situation (see Chapter 4 for an explanation of reverse key indexes).
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