Stretched clustering basics

Before showing my preferred solution for Oracle stretched high availability clusters, first some clustering basics.

Active/passive versus Active/Active clusters

NASA cluster

NASA cluster

Most clustering software is based on active/passive scenarios. You have a system (say, a database) that is running on a set of resources (i.e. a server, to keep it simple) and you have another system (a standby system) that is ready to run the system (failover) but is not actually running it at the same time.

An Active/Active system in general means both systems are active at the same time. There is some confusion as this can mean that the standby system is used for other processing (say, A is production and B is standby but currently running acceptance or testing environments).

By my definition, active/active clustering describes a cluster where all cluster nodes (systems) are processing against the same data set at the same time. There aren’t many products that can do this, especially in the database world. One of the few exceptions is Oracle RAC.

Read more of this post