Multiple residency refers to multiple database servers and their associated shared memory and disk structures that coexist on a single computer.

When you set up multiple independent database server environments on the same computer, you can do the following tasks:
  • Separate production and development environments to protect the production system from the unpredictable nature of the development environment.
  • Isolate sensitive applications or databases that are critically important, either to increase security or to accommodate more frequent backups than most databases require.

    When you use multiple residency, each database server has its own configuration file. Thus, you can create a configuration file for each database server that meets its special requirements for backups, shared-memory use, and tuning priorities.

  • Test distributed data transactions on a single computer. If you are developing an application for use on a network, you can use local loopback to simulate distributed data and testing on a single computer. Later, when a network is ready, you can use the application without changes to application source code.
When you plan for multiple residency on a computer, consider the following factors:
  • Storage space

    Each database server must have its own dedicated storage space. You cannot use the same disk space for more than one instance of a database server. When you prepare another database server, you must repeat some of the planning that you did to install the first database server. For example, you must consider these factors:

    • UNIX, Linux: Whether the files are buffered or unbuffered, and whether the files share a disk partition with another application.
    • The location of mirrored disks, if you plan to use mirroring.
    • The location of the message log.
    • The type of backups that you run.
  • Shared memory

    Each database server has dedicated shared memory. Your computer must have enough shared memory for all the database servers.

Running multiple database servers on the same computer is not as efficient as running one database server. You must balance the advantages of separate database servers with the extra performance cost.