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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>34.8. The Fast-Path Interface</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="libpq-cancel.html" title="34.7. Canceling Queries in Progress" /><link rel="next" href="libpq-notify.html" title="34.9. Asynchronous Notification" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">34.8. The Fast-Path Interface</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="libpq-cancel.html" title="34.7. Canceling Queries in Progress">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="libpq.html" title="Chapter 34. libpq — C Library">Up</a></td><th width="60%" align="center">Chapter 34. <span class="application">libpq</span> — C Library</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="libpq-notify.html" title="34.9. Asynchronous Notification">Next</a></td></tr></table><hr /></div><div class="sect1" id="LIBPQ-FASTPATH"><div class="titlepage"><div><div><h2 class="title" style="clear: both">34.8. The Fast-Path Interface <a href="#LIBPQ-FASTPATH" class="id_link">#</a></h2></div></div></div><a id="id-1.7.3.15.2" class="indexterm"></a><p>
<span class="productname">PostgreSQL</span> provides a fast-path interface
to send simple function calls to the server.
</p><div class="tip"><h3 class="title">Tip</h3><p>
This interface is somewhat obsolete, as one can achieve similar
performance and greater functionality by setting up a prepared
statement to define the function call. Then, executing the statement
with binary transmission of parameters and results substitutes for a
fast-path function call.
</p></div><p>
The function <code class="function" id="LIBPQ-PQFN">PQfn</code><a id="id-1.7.3.15.5.2" class="indexterm"></a>
requests execution of a server function via the fast-path interface:
</p><pre class="synopsis">
PGresult *PQfn(PGconn *conn,
int fnid,
int *result_buf,
int *result_len,
int result_is_int,
const PQArgBlock *args,
int nargs);
typedef struct
{
int len;
int isint;
union
{
int *ptr;
int integer;
} u;
} PQArgBlock;
</pre><p>
</p><p>
The <em class="parameter"><code>fnid</code></em> argument is the OID of the function to be
executed. <em class="parameter"><code>args</code></em> and <em class="parameter"><code>nargs</code></em> define the
parameters to be passed to the function; they must match the declared
function argument list. When the <em class="parameter"><code>isint</code></em> field of a
parameter structure is true, the <em class="parameter"><code>u.integer</code></em> value is sent
to the server as an integer of the indicated length (this must be
2 or 4 bytes); proper byte-swapping occurs. When <em class="parameter"><code>isint</code></em>
is false, the indicated number of bytes at <em class="parameter"><code>*u.ptr</code></em> are
sent with no processing; the data must be in the format expected by
the server for binary transmission of the function's argument data
type. (The declaration of <em class="parameter"><code>u.ptr</code></em> as being of
type <code class="type">int *</code> is historical; it would be better to consider
it <code class="type">void *</code>.)
<em class="parameter"><code>result_buf</code></em> points to the buffer in which to place
the function's return value. The caller must have allocated sufficient
space to store the return value. (There is no check!) The actual result
length in bytes will be returned in the integer pointed to by
<em class="parameter"><code>result_len</code></em>. If a 2- or 4-byte integer result
is expected, set <em class="parameter"><code>result_is_int</code></em> to 1, otherwise
set it to 0. Setting <em class="parameter"><code>result_is_int</code></em> to 1 causes
<span class="application">libpq</span> to byte-swap the value if necessary, so that it
is delivered as a proper <code class="type">int</code> value for the client machine;
note that a 4-byte integer is delivered into <em class="parameter"><code>*result_buf</code></em>
for either allowed result size.
When <em class="parameter"><code>result_is_int</code></em> is 0, the binary-format byte string
sent by the server is returned unmodified. (In this case it's better
to consider <em class="parameter"><code>result_buf</code></em> as being of
type <code class="type">void *</code>.)
</p><p>
<code class="function">PQfn</code> always returns a valid
<code class="structname">PGresult</code> pointer, with
status <code class="literal">PGRES_COMMAND_OK</code> for success
or <code class="literal">PGRES_FATAL_ERROR</code> if some problem was encountered.
The result status should be
checked before the result is used. The caller is responsible for
freeing the <code class="structname">PGresult</code> with
<a class="xref" href="libpq-exec.html#LIBPQ-PQCLEAR"><code class="function">PQclear</code></a> when it is no longer needed.
</p><p>
To pass a NULL argument to the function, set
the <em class="parameter"><code>len</code></em> field of that parameter structure
to <code class="literal">-1</code>; the <em class="parameter"><code>isint</code></em>
and <em class="parameter"><code>u</code></em> fields are then irrelevant.
</p><p>
If the function returns NULL, <em class="parameter"><code>*result_len</code></em> is set
to <code class="literal">-1</code>, and <em class="parameter"><code>*result_buf</code></em> is not
modified.
</p><p>
Note that it is not possible to handle set-valued results when using
this interface. Also, the function must be a plain function, not an
aggregate, window function, or procedure.
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