An application that maintains state typically stores that state in database tables. Because each conversation group has a unique identifier, that identifier is typically used as a key for the state table. Service Broker also provides message retention for applications that must preserve the precise messages sent and received.
Many applications do not require state. In general, an application maintains state if the task involves more than one message, and there is information about the task that cannot be stored in the existing tables for the database.
For example, an application that looks up and returns customer information does not require state, and does not use a state table. On the other hand, an application that manages order fulfillment generates requests to several other services. A program that coordinates requests to other services often uses a state table to track the requests. The application updates the data tables and clears the state table when all of the requests have completed successfully. If a request returns an error, the application resends the request, or uses the state table to send a compensating request.
An application may also use a state table for auditing or logging purposes. The application saves the important information about each request to the state table. In this case, the application does not delete information the state table when a conversation completes.
Some applications may require a precise record of the messages sent and received while the conversation is active. For this scenario, Service Broker provides message retention.