.\" This is -*-nroff-*-
.\" XXX standard disclaimer belongs here....
.\" $Header: /usr/local/devel/postgres/src/ref/RCS/fastpath.3pqsrc,v 1.9 1993/01/26 02:43:13 aoki Exp $
.TH INTRODUCTION "FAST PATH" 01/23/93
.XA 0 "Section 6 \(em Fast Path"
.BH "SECTION 6 \(em FAST PATH"
.SH SYNOPSIS
.(l
\fBretrieve (\fPretval \fB=\fP function\fB(\fP[ arg {\fB,\fP arg } ]\fB))\fP
.)l
.SH DESCRIPTION
\*(PG allows any valid \*(PG function to be called in this way.  Prior
implementations of
.BR "fast path"
allowed user functions to be called directly.  For now, the above
syntax should be used, with arguments cast into the appropriate types.
By executing the above type of query, control transfers completely to
the user function; any user function can access any \*(PG function or
any global variable in the \*(PG address space.
.PP
There are six levels at which calls can be performed:
.IP 1)
Traffic cop level
.br
If a function wants to execute a \*(PG command and pass a string
representation, this level is appropriate.
.IP 2)
Parser
.br
A function can access the \*(PG parser, passing a string and
getting a parse tree in return.
.IP 3)
Query optimizer
.br
A function can call the query optimizer, passing it a parse tree
and obtaining a query plan in return.
.IP 4)
Executor
.br
A function can call the executor and pass it a query plan to be executed.
.IP 5)
Access methods
.br
A function can directly call the access methods if it wishes.
.IP 6)
Function manager
.br
A function can call other functions using this level.
.PP
Documentation of layers 1-6 will appear at some future time.
Meanwhile, fast path users must consult the source code for function
names and arguments at each level.
.PP
It should be noted that users who are concerned with ultimate
performance can bypass the query language completely and directly call
functions that in turn interact with the access methods.  On the other
hand, a user can implement a new query language by coding a function
with an internal parser that then calls the \*(PG optimizer and
executor.  Complete flexibility to use the pieces of \*(PG as a tool
kit is thereby provided.