Oracle Tips by Burleson

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

Cache Fusion Scenarios

Scenario 1

Figure 7.5 (a) shows Scenario 1, where a typical data block is requested from another instance where it is in shared access mode with a local role. Instance(1) desires to read a data block and it makes a request to the GCS, which keeps track of the resources, location, and status. The GCS in turn forwards the request to owning instance(2).

Figure 7.5(a) Read/Read Cache Fusion – GCS processing

The holding instance (Instance 2) transmits a copy of the block to the requesting instance (Instance 1), but keeps the resource in shared mode and also retains the local role.

Instance 2 now informs the GCS of its own resource disposition (S, L) and also that of the instance that sent the block (S, L). Thus, there is no disk read involved. The block transfer took place through the high-speed private interconnect.