In the previous lesson, we discussed how to set up and use instance affinity. In
this lesson, we take a look at a different concept: disk affinity. The OPS system contains a group of interconnected instances and supporting data files stored on disks. If an instance is located on the same node as a data file, the two are considered to have
node affinity[1].
The idea is expanded further to
disk affinity[2], which means that a database instance is located on the same node as a disk that contains the data file.
The Optimizer uses disk affinity to decide which instance runs each component of a parallel query. The Optimizer looks at the data and finds the instance closest to the partition that it needs for the portion of the parallel transaction that the instance is to run. This improves response time by causing the data access to be done as much as possible within a local node, reducing traffic on the network.
