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  Oracle Database Tips by Donald Burleson

Oracle10g Grid Computing with RAC
Chapter 7 - Cache Fusion and Inter Instance Coordination


The less synchronization necessary, the better the system's performance and scalability will be. The overhead of synchronization can be very expensive if there is excessive inter-node communication. Block access times vary, as shown in Fig. 7.4. According to Oracle studies, accessing a block within the local cache is many times faster than accessing a block in a remote cache (or buffer of another instance in the cluster). At the same time, accessing a block from disk is even more expensive. A combination of local cache block access with occasional access to remote cache blocks gives good performance levels.


Figure 7.4 Block Access Times

GCS Resource Modes and Roles

Because of data block transfers among multiple instances, the same data block can exist in multiple caches. The resource mode is defined as a concurrency control that establishes global access rights for instances in a cluster. The data block (or GCS resource) can be held in different resource modes, depending on whether a resource holder intends to modify the data or read the data. The modes are as follows:

The above text is an excerpt from:

Oracle 10g Grid & Real Application Clusters
Oracle 10g Grid Computing with RAC
ISBN 0-9744355-4-6

by Mike Ault, Madhu Tumma


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