Cache Fusion In Oracle Rac

cache fusion is disk less cache coherency mechanism in Oracle RAC that provides copies of data blocks directly from one instance’s memory cache (in which that block is available) to other instance (instance which is request for specific data block).  Cache Fusion provides single buffer cache (for all instances in cluster) through interconnect.

In Single Node oracle database, an instance looking for data block first checks in cache, if block is not in cache then goes to disk to pull block from disk to cache and return block to client.

In RAC Database there is remote cache so instance should look not only in local cache (cache local to instance) but on remote cache (cache on remote instance). If cache is available in local cache then it should return data block from local cache; if data block is not in local cache, instead of going to disk it should first go to remote cache (remote instance) to check if block is available in local cache (via interconnect)

This is because of accessing data block from remote cache is faster than accessing it from disk.