<?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>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 Vsnapshot" /><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 11.5 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>
