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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>64.4. Implementation</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="gist-extensibility.html" title="64.3. Extensibility" /><link rel="next" href="gist-examples.html" title="64.5. Examples" /></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">64.4. Implementation</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="gist-extensibility.html" title="64.3. Extensibility">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="gist.html" title="Chapter 64. GiST Indexes">Up</a></td><th width="60%" align="center">Chapter 64. GiST 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="gist-examples.html" title="64.5. Examples">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="GIST-IMPLEMENTATION"><div class="titlepage"><div><div><h2 class="title" style="clear: both">64.4. Implementation</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="gist-implementation.html#GIST-BUFFERING-BUILD">64.4.1. GiST Buffering Build</a></span></dt></dl></div><div class="sect2" id="GIST-BUFFERING-BUILD"><div class="titlepage"><div><div><h3 class="title">64.4.1. GiST Buffering Build</h3></div></div></div><p>
- Building large GiST indexes by simply inserting all the tuples tends to be
- slow, because if the index tuples are scattered across the index and the
- index is large enough to not fit in cache, the insertions need to perform
- a lot of random I/O. Beginning in version 9.2, PostgreSQL supports a more
- efficient method to build GiST indexes based on buffering, which can
- dramatically reduce the number of random I/Os needed for non-ordered data
- sets. For well-ordered data sets the benefit is smaller or non-existent,
- because only a small number of pages receive new tuples at a time, and
- those pages fit in cache even if the index as whole does not.
- </p><p>
- However, buffering index build needs to call the <code class="function">penalty</code>
- function more often, which consumes some extra CPU resources. Also, the
- buffers used in the buffering build need temporary disk space, up to
- the size of the resulting index. Buffering can also influence the quality
- of the resulting index, in both positive and negative directions. That
- influence depends on various factors, like the distribution of the input
- data and the operator class implementation.
- </p><p>
- By default, a GiST index build switches to the buffering method when the
- index size reaches <a class="xref" href="runtime-config-query.html#GUC-EFFECTIVE-CACHE-SIZE">effective_cache_size</a>. It can
- be manually turned on or off by the <code class="literal">buffering</code> parameter
- to the CREATE INDEX command. The default behavior is good for most cases,
- but turning buffering off might speed up the build somewhat if the input
- data is ordered.
- </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="gist-extensibility.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="gist.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="gist-examples.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">64.3. Extensibility </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 64.5. Examples</td></tr></table></div></body></html>
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