What Is an Instance?

A database server consists of a database and a database instance:

• A database is a collection of data that is treated as a unit.

• A database instance consists of background processes and memory buffers.

Depending on your needs, you can create more than one instance. Multiple instances require additional machine resources, such as processes and memory. On smaller systems, multiple instances could overload your system.

If you are using multiple instances, you might typically set up a separate instance for production and a separate instance for test or training. This allows for maximum flexibility in managing each database.

When multiple data areas share a single database instance, either the SCHEMA parameter or the LOGINNAME/PASSWORD combination in the database configuration file identifies each database. The reason for setting up multiple data areas within a single instance is that each instance has its own complete set of database processes running. In contrast, putting each data area's database within separate instances requires additional processor and memory needs and can easily overload smaller systems.

For more information on using single versus multiple instances, see your Oracle documentation.