Author: This chapter originally appeared as a part of Simkovics,
1998, Stefan Simkovics' Master's Thesis prepared at Vienna
University of Technology under the direction of O.Univ.Prof.Dr.
Georg Gottlob and Univ.Ass. Mag. Katrin Seyr. This chapter gives
an overview of the internal structure of the backend of
Postgres. After having read the following sections you should
have an idea of how a query is processed. Don't expect a
detailed description here (I think such a description dealing
with all data structures and functions used within Postgres
would exceed 1000 pages!). This chapter is intended to help
understanding the general control and data flow within the
backend from receiving a query to sending the results. Here we
give a short overview of the stages a query has to pass in order
to obtain a result. A connection from an application program to
the Postgres server has to be established. The application
program transmits a query to the server and receives the results
sent back by the server. The parser sta