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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>F.44. uuid-ossp</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="unaccent.html" title="F.43. unaccent" /><link rel="next" href="xml2.html" title="F.45. xml2" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">F.44. uuid-ossp</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="unaccent.html" title="F.43. unaccent">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="contrib.html" title="Appendix F. Additional Supplied Modules">Up</a></td><th width="60%" align="center">Appendix F. Additional Supplied Modules</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 11.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="xml2.html" title="F.45. xml2">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="UUID-OSSP"><div class="titlepage"><div><div><h2 class="title" style="clear: both">F.44. uuid-ossp</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="uuid-ossp.html#id-1.11.7.53.4">F.44.1. <code class="literal">uuid-ossp</code> Functions</a></span></dt><dt><span class="sect2"><a href="uuid-ossp.html#id-1.11.7.53.5">F.44.2. Building <code class="filename">uuid-ossp</code></a></span></dt><dt><span class="sect2"><a href="uuid-ossp.html#id-1.11.7.53.6">F.44.3. Author</a></span></dt></dl></div><a id="id-1.11.7.53.2" class="indexterm"></a><p>
The <code class="filename">uuid-ossp</code> module provides functions to generate universally
unique identifiers (UUIDs) using one of several standard algorithms. There
are also functions to produce certain special UUID constants.
</p><div class="sect2" id="id-1.11.7.53.4"><div class="titlepage"><div><div><h3 class="title">F.44.1. <code class="literal">uuid-ossp</code> Functions</h3></div></div></div><p>
<a class="xref" href="uuid-ossp.html#UUID-OSSP-FUNCTIONS" title="Table F.32. Functions for UUID Generation">Table F.32</a> shows the functions available to
generate UUIDs.
The relevant standards ITU-T Rec. X.667, ISO/IEC 9834-8:2005, and RFC
4122 specify four algorithms for generating UUIDs, identified by the
version numbers 1, 3, 4, and 5. (There is no version 2 algorithm.)
Each of these algorithms could be suitable for a different set of
applications.
</p><div class="table" id="UUID-OSSP-FUNCTIONS"><p class="title"><strong>Table F.32. Functions for UUID Generation</strong></p><div class="table-contents"><table class="table" summary="Functions for UUID Generation" border="1"><colgroup><col /><col /></colgroup><thead><tr><th>Function</th><th>Description</th></tr></thead><tbody><tr><td><code class="function">uuid_generate_v1()</code><a id="id-1.11.7.53.4.3.2.2.1.1.2" class="indexterm"></a></td><td>
<p>
This function generates a version 1 UUID. This involves the MAC
address of the computer and a time stamp. Note that UUIDs of this
kind reveal the identity of the computer that created the identifier
and the time at which it did so, which might make it unsuitable for
certain security-sensitive applications.
</p>
</td></tr><tr><td><code class="function">uuid_generate_v1mc()</code><a id="id-1.11.7.53.4.3.2.2.2.1.2" class="indexterm"></a></td><td>
<p>
This function generates a version 1 UUID but uses a random multicast
MAC address instead of the real MAC address of the computer.
</p>
</td></tr><tr><td><code class="function">uuid_generate_v3(namespace uuid, name text)</code><a id="id-1.11.7.53.4.3.2.2.3.1.2" class="indexterm"></a></td><td>
<p>
This function generates a version 3 UUID in the given namespace using
the specified input name. The namespace should be one of the special
constants produced by the <code class="function">uuid_ns_*()</code> functions shown
in <a class="xref" href="uuid-ossp.html#UUID-OSSP-CONSTANTS" title="Table F.33. Functions Returning UUID Constants">Table F.33</a>. (It could be any UUID in theory.) The name is an identifier
in the selected namespace.
</p>
<p>
For example:
</p><pre class="programlisting">
SELECT uuid_generate_v3(uuid_ns_url(), 'http://www.postgresql.org');
</pre><p>
The name parameter will be MD5-hashed, so the cleartext cannot be
derived from the generated UUID.
The generation of UUIDs by this method has no random or
environment-dependent element and is therefore reproducible.
</p>
</td></tr><tr><td><code class="literal">uuid_generate_v4()</code></td><td>
<p>
This function generates a version 4 UUID, which is derived entirely
from random numbers.
</p>
</td></tr><tr><td><code class="literal">uuid_generate_v5(namespace uuid, name text)</code></td><td>
<p>
This function generates a version 5 UUID, which works like a version 3
UUID except that SHA-1 is used as a hashing method. Version 5 should
be preferred over version 3 because SHA-1 is thought to be more secure
than MD5.
</p>
</td></tr></tbody></table></div></div><br class="table-break" /><div class="table" id="UUID-OSSP-CONSTANTS"><p class="title"><strong>Table F.33. Functions Returning UUID Constants</strong></p><div class="table-contents"><table class="table" summary="Functions Returning UUID Constants" border="1"><colgroup><col /><col /></colgroup><tbody><tr><td><code class="literal">uuid_nil()</code></td><td>
<p>
A <span class="quote">“<span class="quote">nil</span>”</span> UUID constant, which does not occur as a real UUID.
</p>
</td></tr><tr><td><code class="literal">uuid_ns_dns()</code></td><td>
<p>
Constant designating the DNS namespace for UUIDs.
</p>
</td></tr><tr><td><code class="literal">uuid_ns_url()</code></td><td>
<p>
Constant designating the URL namespace for UUIDs.
</p>
</td></tr><tr><td><code class="literal">uuid_ns_oid()</code></td><td>
<p>
Constant designating the ISO object identifier (OID) namespace for
UUIDs. (This pertains to ASN.1 OIDs, which are unrelated to the OIDs
used in <span class="productname">PostgreSQL</span>.)
</p>
</td></tr><tr><td><code class="literal">uuid_ns_x500()</code></td><td>
<p>
Constant designating the X.500 distinguished name (DN) namespace for
UUIDs.
</p>
</td></tr></tbody></table></div></div><br class="table-break" /></div><div class="sect2" id="id-1.11.7.53.5"><div class="titlepage"><div><div><h3 class="title">F.44.2. Building <code class="filename">uuid-ossp</code></h3></div></div></div><p>
Historically this module depended on the OSSP UUID library, which accounts
for the module's name. While the OSSP UUID library can still be found
at <a class="ulink" href="http://www.ossp.org/pkg/lib/uuid/" target="_top">http://www.ossp.org/pkg/lib/uuid/</a>, it is not well
maintained, and is becoming increasingly difficult to port to newer
platforms. <code class="filename">uuid-ossp</code> can now be built without the OSSP
library on some platforms. On FreeBSD, NetBSD, and some other BSD-derived
platforms, suitable UUID creation functions are included in the
core <code class="filename">libc</code> library. On Linux, macOS, and some other
platforms, suitable functions are provided in the <code class="filename">libuuid</code>
library, which originally came from the <code class="literal">e2fsprogs</code> project
(though on modern Linux it is considered part
of <code class="literal">util-linux-ng</code>). When invoking <code class="filename">configure</code>,
specify <code class="option">--with-uuid=bsd</code> to use the BSD functions,
or <code class="option">--with-uuid=e2fs</code> to
use <code class="literal">e2fsprogs</code>' <code class="filename">libuuid</code>, or
<code class="option">--with-uuid=ossp</code> to use the OSSP UUID library.
More than one of these libraries might be available on a particular
machine, so <code class="filename">configure</code> does not automatically choose one.
</p><div class="note"><h3 class="title">Note</h3><p>
If you only need randomly-generated (version 4) UUIDs,
consider using the <code class="function">gen_random_uuid()</code> function
from the <a class="xref" href="pgcrypto.html" title="F.25. pgcrypto">pgcrypto</a> module instead.
</p></div></div><div class="sect2" id="id-1.11.7.53.6"><div class="titlepage"><div><div><h3 class="title">F.44.3. Author</h3></div></div></div><p>
Peter Eisentraut <code class="email"><<a class="email" href="mailto:peter_e@gmx.net">peter_e@gmx.net</a>></code>
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