What Is an Instance?

When you install SQL-NS, you get a set of tools and supporting files placed on your computer, along with the Registry settings that the installer and uninstaller need. However, the installer does not create any SQL-NS instances. You must use the SQL-NS tools to create instances when you need them, to host your various SQL-NS applications.

An instance is a named configuration of SQL-NS that contains one or more SQL-NS applications. Think of an instance as a container that groups a set of applications with common security and administration settings. Subscriber information is shared among applications within an instance: When a new subscriber registers (using a subscription management interface such as the one we'll build in Chapter 7, "The SQL-NS Subscription Management API"), the registration information is stored at the instance level and made available to all applications in the instance.

Several parts make up the physical representation of an instance:

• Database objects encapsulating the instance data and logic

• Database objects for each application in the instance

• Metadata in system tables that describes properties of the instance

• Registry keys that store parts of the instance configuration

• A dedicated SQL-NS engine that hosts the runtime components of the applications in the instance

• Performance counters used to monitor the instance

These are shown in Figure 4.1. In this chapter, we'll create a simple instance and then examine each of these parts in detail.

Figure 4.1. Parts of a SQL-NS instance.