doc/src/sgml/uuid-ossp.sgml

   1 <!-- $PostgreSQL$ -->
   2
   3 <sect1 id="uuid-ossp">
   4  <title>uuid-ossp</title>
   5
   6  <indexterm zone="uuid-ossp">
   7   <primary>uuid-ossp</primary>
   8  </indexterm>
   9
  10  <para>
  11   The <filename>uuid-ossp</> module provides functions to generate universally
  12   unique identifiers (UUIDs) using one of several standard algorithms.  There
  13   are also functions to produce certain special UUID constants.
  14  </para>
  15
  16  <para>
  17   This module depends on the OSSP UUID library, which can be found at
  18   <ulink url="http://www.ossp.org/pkg/lib/uuid/"></ulink>.
  19  </para>
  20
  21  <sect2>
  22   <title><literal>uuid-ossp</literal> Functions</title>
  23
  24   <para>
  25    The relevant standards ITU-T Rec. X.667, ISO/IEC 9834-8:2005, and RFC
  26    4122 specify four algorithms for generating UUIDs, identified by the
  27    version numbers 1, 3, 4, and 5.  (There is no version 2 algorithm.)
  28    Each of these algorithms could be suitable for a different set of
  29    applications.
  30   </para>
  31
  32   <table>
  33    <title>Functions for UUID Generation</title>
  34    <tgroup cols="2">
  35     <thead>
  36      <row>
  37       <entry>Function</entry>
  38       <entry>Description</entry>
  39      </row>
  40     </thead>
  41     <tbody>
  42      <row>
  43       <entry><literal>uuid_generate_v1()</literal></entry>
  44       <entry>
  45        <para>
  46         This function generates a version 1 UUID.  This involves the MAC
  47         address of the computer and a time stamp.  Note that UUIDs of this
  48         kind reveal the identity of the computer that created the identifier
  49         and the time at which it did so, which might make it unsuitable for
  50         certain security-sensitive applications.
  51        </para>
  52       </entry>
  53      </row>
  54      <row>
  55       <entry><literal>uuid_generate_v1mc()</literal></entry>
  56       <entry>
  57        <para>
  58         This function generates a version 1 UUID but uses a random multicast
  59         MAC address instead of the real MAC address of the computer.
  60        </para>
  61       </entry>
  62      </row>
  63      <row>
  64       <entry><literal>uuid_generate_v3(namespace uuid, name text)</literal></entry>
  65       <entry>
  66        <para>
  67         This function generates a version 3 UUID in the given namespace using
  68         the specified input name.  The namespace should be one of the special
  69         constants produced by the <function>uuid_ns_*()</> functions shown
  70         below.  (It could be any UUID in theory.)  The name is an identifier
  71         in the selected namespace.
  72        </para>
  73       </entry>
  74      </row>
  75      <row>
  76       <entry><literal>uuid_generate_v4()</literal></entry>
  77       <entry>
  78        <para>
  79         This function generates a version 4 UUID, which is derived entirely
  80         from random numbers.
  81        </para>
  82       </entry>
  83      </row>
  84      <row>
  85       <entry><literal>uuid_generate_v5(namespace uuid, name text)</literal></entry>
  86       <entry>
  87        <para>
  88         This function generates a version 5 UUID, which works like a version 3
  89         UUID except that SHA-1 is used as a hashing method.  Version 5 should
  90         be preferred over version 3 because SHA-1 is thought to be more secure
  91         than MD5.
  92        </para>
  93       </entry>
  94      </row>
  95     </tbody>
  96    </tgroup>
  97   </table>
  98
  99   <para>
 100    For example:
 101
 102    <programlisting>
 103     SELECT uuid_generate_v3(uuid_ns_url(), 'http://www.postgresql.org');
 104    </programlisting>
 105
 106    The name parameter will be MD5-hashed, so the cleartext cannot be
 107    derived from the generated UUID.
 108    The generation of UUIDs by this method has no random or
 109    environment-dependent element and is therefore reproducible.
 110   </para>
 111
 112   <table>
 113    <title>Functions Returning UUID Constants</title>
 114    <tgroup cols="2">
 115     <tbody>
 116      <row>
 117       <entry><literal>uuid_nil()</literal></entry>
 118       <entry>
 119        <para>
 120         A <quote>nil</> UUID constant, which does not occur as a real UUID.
 121        </para>
 122       </entry>
 123      </row>
 124      <row>
 125       <entry><literal>uuid_ns_dns()</literal></entry>
 126       <entry>
 127        <para>
 128         Constant designating the DNS namespace for UUIDs.
 129        </para>
 130       </entry>
 131      </row>
 132      <row>
 133       <entry><literal>uuid_ns_url()</literal></entry>
 134       <entry>
 135        <para>
 136         Constant designating the URL namespace for UUIDs.
 137        </para>
 138       </entry>
 139      </row>
 140      <row>
 141       <entry><literal>uuid_ns_oid()</literal></entry>
 142       <entry>
 143        <para>
 144         Constant designating the ISO object identifier (OID) namespace for
 145         UUIDs.  (This pertains to ASN.1 OIDs, which are unrelated to the OIDs
 146         used in <productname>PostgreSQL</>.)
 147        </para>
 148       </entry>
 149      </row>
 150      <row>
 151       <entry><literal>uuid_ns_x500()</literal></entry>
 152       <entry>
 153        <para>
 154         Constant designating the X.500 distinguished name (DN) namespace for
 155         UUIDs.
 156        </para>
 157       </entry>
 158      </row>
 159     </tbody>
 160    </tgroup>
 161   </table>
 162  </sect2>
 163
 164  <sect2>
 165   <title>Author</title>
 166
 167   <para>
 168    Peter Eisentraut <email>peter_e@gmx.net</email>
 169   </para>
 170
 171  </sect2>
 172
 173 </sect1>