Parsing Engine

A Parsing Engine (PE) is a virtual processor (vproc). It is made up of the following software components:

• Session Control
• Parser
• Optimizer
• Dispatcher

Parsing Engine

Each PE can support a maximum of 120 sessions.

The Session Control component verifies the request for session authorization (user names and passwords), and either allows or disallows the request.

The Parser does the following:

• Interprets the SQL statement received from the application.
• Verifies SQL requests for the proper syntax and evaluates them semantically.
• Consults the Data Dictionary to ensure that all objects exist and that the user has authority to access them. 

The Optimizer is cost-based and develops the least expensive plan (in terms of time) to return the requested response set.The optimizer must know about system configuration, available units of parallelism (AMPs and PE's), and data demographics. The Teradata Optimizer is robust and intelligent. The optimizer enables Teradata to handle multiple complex, ad hoc queries efficiently. It is parallel-aware and cost-based and uses full look-ahead capability.

The Dispatcher controls the sequence in which the steps are executed and passes the steps received from the optimizer onto the BYNET for execution by the AMPs.

After the AMPs process the steps, the PE receives their responses over the BYNET.

The Dispatcher builds a response message and sends the message back to the user.