Oracle Fault Tolerance
The successor to Oracle Parallel Server is the RAC (Real Application Cluster). In a RAC setup multiple instances access a single database. This implies that if an instance crashes, there are other instances that a connection can fail over to. This includes transactional fail over as well wherein a transaction can be retried on another instance when the one it was previously executing on has crashed.
Note: if the disk that the database is mounted on crashes then RAC will be useful as well.
In an active-active setup, all instances are active and thus the benefits include:
- Fault tolerance through fail over
- Scalability through load balancing
HACMP (High Availability Cluster Multi-Processing) versus RAC
HACMP is a clusterware that can be used with Oracle RAC as well. Either Oracle Clusterware or HACMP can be used to provide these services bulleted above. If there is more than Oracle (other apps such as NFS server etc) that has to be HA then use HACMP as the clusterware.
HACMP and Oralce Clusterware are complimentary
Note: SMP => Symmetric MultiProcessing.