Query Processing

A typical interaction with Ingres consists of at least two processes:

• An Ingres tool or application
• DBMS Server process

The Ingres Tool or Application Process

The Ingres tool or application performs the following actions:

• Takes user input and issues a query that is sent to the DBMS Server.
• Formats, optimizes, and executes the query on behalf of the user.
• Displays the resulted data returned by the DBMS Server.

DBMS Server Process

The Ingres DBMS Server is a multi-threaded process. It can execute queries for a large number of users, each running an Ingres tool. Even though it is a single process, the DBMS Server can execute queries as multiple "sessions" on behalf of multiple users. The ipm, iimonitor, and Visual Performance Monitor tools lets you view which sessions are running in the DBMS Server at any moment.

Query Environment

When a thread or session executes a query inside the DBMS Server, it does so in a query environment. The query environment consists of:

• A quantity of resources available from the operating system for use by the session.
• The rules under which the query is executed. These rules reflect which query language is used, which locking strategy is employed, which diagnostic information is returned, which default behavior Ingres adopts for various query language statements, and so on.