Oracle RAC partitioning Don Burleson

In Shared-Nothing model, also termed as Data-Partitioning Model, each system owns a portion of the database and each partition can only be read or modified by the owning system. [Fig. 3.10] Data Partitioning enables each system to locally cache its portion of the database in processor memory without requiring cross-system communication to provide data access concurrency and coherency controls.

Each server in the cluster has its own independent subset of the data (a partition) it can work on independently without encountering resource contention from other servers. The clustered nodes communicate by passing messages through a network that interconnects the servers. Client requests are automatically routed to the system that owns the particular resource (for example, memory or disk). Only one of the clustered systems can "own" and access a particular resource at a time. In the event of a failure, resource ownership can be dynamically transferred to another system in the cluster.

This architecture has several advantages:

• Shared nothing systems provide for incremental growth.
• Good for read-only databases and decision support applications.
• Failure is local - if one node fails, the other nodes stay up. However, disk system of failed node moves over to the surviving node.

It does suffer from some drawbacks as well:

• More coordination is required.
• More overhead is required in terms of processing or function shipping for a SQL operation working on a data/disk belonging to another node.