Chapter 42. Overview of PostgreSQL Internals
   This chapter gives an overview of the internal structure of the
   backend of PostgreSQL.  After having
   read the following sections you should have an idea of how a query
   is processed. This chapter does not aim to provide a detailed
   description of the internal operation of
   PostgreSQL, as such a document would be
   very extensive. Rather, this chapter is intended to help the reader
   understand the general sequence of operations that occur within the
   backend from the point at which a query is received, to the point
   at which the results are returned to the client.