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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>66.1. Introduction</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 V1.79.1" /><link rel="prev" href="gin.html" title="Chapter 66. GIN Indexes" /><link rel="next" href="gin-builtin-opclasses.html" title="66.2. Built-in Operator Classes" /></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">66.1. Introduction</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="gin.html" title="Chapter 66. GIN Indexes">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="gin.html" title="Chapter 66. GIN Indexes">Up</a></td><th width="60%" align="center">Chapter 66. GIN Indexes</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 12.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="gin-builtin-opclasses.html" title="66.2. Built-in Operator Classes">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="GIN-INTRO"><div class="titlepage"><div><div><h2 class="title" style="clear: both">66.1. Introduction</h2></div></div></div><p>
- <acronym class="acronym">GIN</acronym> stands for Generalized Inverted Index.
- <acronym class="acronym">GIN</acronym> is designed for handling cases where the items
- to be indexed are composite values, and the queries to be handled by
- the index need to search for element values that appear within
- the composite items. For example, the items could be documents,
- and the queries could be searches for documents containing specific words.
- </p><p>
- We use the word <em class="firstterm">item</em> to refer to a composite value that
- is to be indexed, and the word <em class="firstterm">key</em> to refer to an element
- value. <acronym class="acronym">GIN</acronym> always stores and searches for keys,
- not item values per se.
- </p><p>
- A <acronym class="acronym">GIN</acronym> index stores a set of (key, posting list) pairs,
- where a <em class="firstterm">posting list</em> is a set of row IDs in which the key
- occurs. The same row ID can appear in multiple posting lists, since
- an item can contain more than one key. Each key value is stored only
- once, so a <acronym class="acronym">GIN</acronym> index is very compact for cases
- where the same key appears many times.
- </p><p>
- <acronym class="acronym">GIN</acronym> is generalized in the sense that the
- <acronym class="acronym">GIN</acronym> access method code does not need to know the
- specific operations that it accelerates.
- Instead, it uses custom strategies defined for particular data types.
- The strategy defines how keys are extracted from indexed items and
- query conditions, and how to determine whether a row that contains
- some of the key values in a query actually satisfies the query.
- </p><p>
- One advantage of <acronym class="acronym">GIN</acronym> is that it allows the development
- of custom data types with the appropriate access methods, by
- an expert in the domain of the data type, rather than a database expert.
- This is much the same advantage as using <acronym class="acronym">GiST</acronym>.
- </p><p>
- The <acronym class="acronym">GIN</acronym>
- implementation in <span class="productname">PostgreSQL</span> is primarily
- maintained by Teodor Sigaev and Oleg Bartunov. There is more
- information about <acronym class="acronym">GIN</acronym> on their
- <a class="ulink" href="http://www.sai.msu.su/~megera/wiki/Gin" target="_top">website</a>.
- </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="gin.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="gin.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="gin-builtin-opclasses.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 66. GIN Indexes </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 66.2. Built-in Operator Classes</td></tr></table></div></body></html>
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