doc/src/sgml/dict-int.sgml

   1 <!-- $PostgreSQL$ -->
   2
   3 <sect1 id="dict-int">
   4  <title>dict_int</title>
   5
   6  <indexterm zone="dict-int">
   7   <primary>dict_int</primary>
   8  </indexterm>
   9
  10  <para>
  11   <filename>dict_int</> is an example of an add-on dictionary template
  12   for full-text search.  The motivation for this example dictionary is to
  13   control the indexing of integers (signed and unsigned), allowing such
  14   numbers to be indexed while preventing excessive growth in the number of
  15   unique words, which greatly affects the performance of searching.
  16  </para>
  17
  18  <sect2>
  19   <title>Configuration</title>
  20
  21   <para>
  22    The dictionary accepts two options:
  23   </para>
  24
  25   <itemizedlist>
  26    <listitem>
  27     <para>
  28      The <literal>maxlen</> parameter specifies the maximum number of
  29      digits allowed in an integer word.  The default value is 6.
  30     </para>
  31    </listitem>
  32    <listitem>
  33     <para>
  34      The <literal>rejectlong</> parameter specifies whether an overlength
  35      integer should be truncated or ignored.  If <literal>rejectlong</> is
  36      <literal>false</> (the default), the dictionary returns the first
  37      <literal>maxlen</> digits of the integer. If <literal>rejectlong</> is
  38      <literal>true</>, the dictionary treats an overlength integer as a stop
  39      word, so that it will not be indexed.  Note that this also means that
  40      such an integer cannot be searched for.
  41     </para>
  42    </listitem>
  43   </itemizedlist>
  44  </sect2>
  45
  46  <sect2>
  47   <title>Usage</title>
  48
  49   <para>
  50    Running the installation script creates a text search template
  51    <literal>intdict_template</> and a dictionary <literal>intdict</>
  52    based on it, with the default parameters.  You can alter the
  53    parameters, for example
  54
  55 <programlisting>
  56 mydb# ALTER TEXT SEARCH DICTIONARY intdict (MAXLEN = 4, REJECTLONG = true);
  57 ALTER TEXT SEARCH DICTIONARY
  58 </programlisting>
  59
  60    or create new dictionaries based on the template.
  61   </para>
  62
  63   <para>
  64    To test the dictionary, you can try
  65
  66 <programlisting>
  67 mydb# select ts_lexize('intdict', '12345678');
  68  ts_lexize
  69 -----------
  70  {123456}
  71 </programlisting>
  72
  73    but real-world usage will involve including it in a text search
  74    configuration as described in <xref linkend="textsearch">.
  75    That might look like this:
  76
  77 <programlisting>
  78 ALTER TEXT SEARCH CONFIGURATION english
  79     ALTER MAPPING FOR int, uint WITH intdict;
  80 </programlisting>
  81
  82   </para>
  83  </sect2>
  84
  85 </sect1>