<?xml version="1.0" encoding="UTF-8" standalone="no"?> <!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 Vsnapshot" /><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 11.5 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>
