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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>Chapter 15. Parallel Query</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="non-durability.html" title="14.5. Non-Durable Settings" /><link rel="next" href="how-parallel-query-works.html" title="15.1. How Parallel Query Works" /></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">Chapter 15. Parallel Query</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="non-durability.html" title="14.5. Non-Durable Settings">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="sql.html" title="Part II. The SQL Language">Up</a></td><th width="60%" align="center">Part II. The SQL Language</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="how-parallel-query-works.html" title="15.1. How Parallel Query Works">Next</a></td></tr></table><hr></hr></div><div class="chapter" id="PARALLEL-QUERY"><div class="titlepage"><div><div><h2 class="title">Chapter 15. Parallel Query</h2></div></div></div><div class="toc"><p><strong>Table of Contents</strong></p><dl class="toc"><dt><span class="sect1"><a href="how-parallel-query-works.html">15.1. How Parallel Query Works</a></span></dt><dt><span class="sect1"><a href="when-can-parallel-query-be-used.html">15.2. When Can Parallel Query Be Used?</a></span></dt><dt><span class="sect1"><a href="parallel-plans.html">15.3. Parallel Plans</a></span></dt><dd><dl><dt><span class="sect2"><a href="parallel-plans.html#PARALLEL-SCANS">15.3.1. Parallel Scans</a></span></dt><dt><span class="sect2"><a href="parallel-plans.html#PARALLEL-JOINS">15.3.2. Parallel Joins</a></span></dt><dt><span class="sect2"><a href="parallel-plans.html#PARALLEL-AGGREGATION">15.3.3. Parallel Aggregation</a></span></dt><dt><span class="sect2"><a href="parallel-plans.html#PARALLEL-APPEND">15.3.4. Parallel Append</a></span></dt><dt><span class="sect2"><a href="parallel-plans.html#PARALLEL-PLAN-TIPS">15.3.5. Parallel Plan Tips</a></span></dt></dl></dd><dt><span class="sect1"><a href="parallel-safety.html">15.4. Parallel Safety</a></span></dt><dd><dl><dt><span class="sect2"><a href="parallel-safety.html#PARALLEL-LABELING">15.4.1. Parallel Labeling for Functions and Aggregates</a></span></dt></dl></dd></dl></div><a id="id-1.5.14.2" class="indexterm"></a><p>
- <span class="productname">PostgreSQL</span> can devise query plans which can leverage
- multiple CPUs in order to answer queries faster. This feature is known
- as parallel query. Many queries cannot benefit from parallel query, either
- due to limitations of the current implementation or because there is no
- imaginable query plan which is any faster than the serial query plan.
- However, for queries that can benefit, the speedup from parallel query
- is often very significant. Many queries can run more than twice as fast
- when using parallel query, and some queries can run four times faster or
- even more. Queries that touch a large amount of data but return only a
- few rows to the user will typically benefit most. This chapter explains
- some details of how parallel query works and in which situations it can be
- used so that users who wish to make use of it can understand what to expect.
- </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="non-durability.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="sql.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="how-parallel-query-works.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">14.5. Non-Durable Settings </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 15.1. How Parallel Query Works</td></tr></table></div></body></html>
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