Oracle RAC
An Oracle cluster architecture in which multiple database instances concurrently access the same database on shared storage for availability and scale.
In Oracle Real Application Clusters, each node runs its own Oracle instance while the database files are shared. Instances coordinate buffer-cache block ownership and locking information across the cluster interconnect; Cache Fusion is therefore central to RAC behavior.
RAC does not make every workload scale linearly. Workloads that repeatedly modify the same blocks can generate global-cache traffic and interconnect latency. Service placement, partitioning, hot-block analysis, and instance affinity belong in capacity planning. Failure tolerance and horizontal throughput gain are separate properties.
Related: Cache Fusion, Global Cache Service, Oracle Clusterware, SCAN Listener, Oracle Database and PL/SQL.