Oracle Database Tips by Donald Burleson

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

Nature of Cache Fusion

This is where the method of cache fusion plays a key role. For all practical purposes, multiple buffer caches join and act as if they were a single entity. As shown in Figure 7.1, cache buffers from three nodes are fused together to form a single entity and share data blocks. Maintaining consistency among the cached versions of data blocks in multiple instances is called 'cache coherency'. Cache fusion treats multiple buffer caches as one joint global cache, solving data consistency issues internally, without any impact on the application code or design.

Figure 7.1 Global Cache - Cache Fusion in a three-node cluster

Benefits of Cache Fusion

Oracle RAC, with its multiple instances, is able to provide more resources through multiple system global areas (SGA). Cache fusion technology makes it easier to process a very high number of concurrent users and SQL operations without compromising data consistency. It adheres to Oracle's multi-version consistency model and ensures data integrity and data consistency across the instances.

Cache fusion in 9i, implemented fully, creates an environment where users are able to utilize any instance in the cluster without giving undue preference for a particular instance. There is no need for the extra effort of partitioning data access across nodes, as required in earlier versions of parallel servers. Load balancing is more effective in such an environment.