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1<?xml version="1.0" encoding="UTF-8" standalone="no"?>2<!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>13.7. Locking and Indexes</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="mvcc-caveats.html" title="13.6. Caveats" /><link rel="next" href="performance-tips.html" title="Chapter 14. Performance Tips" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">13.7. Locking and Indexes</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="mvcc-caveats.html" title="13.6. Caveats">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="mvcc.html" title="Chapter 13. Concurrency Control">Up</a></td><th width="60%" align="center">Chapter 13. Concurrency Control</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="performance-tips.html" title="Chapter 14. Performance Tips">Next</a></td></tr></table><hr /></div><div class="sect1" id="LOCKING-INDEXES"><div class="titlepage"><div><div><h2 class="title" style="clear: both">13.7. Locking and Indexes <a href="#LOCKING-INDEXES" class="id_link">#</a></h2></div></div></div><a id="id-1.5.12.10.2" class="indexterm"></a><p>3    Though <span class="productname">PostgreSQL</span>4    provides nonblocking read/write access to table5    data, nonblocking read/write access is not currently offered for every6    index access method implemented7    in <span class="productname">PostgreSQL</span>.8    The various index types are handled as follows:9 10    </p><div class="variablelist"><dl class="variablelist"><dt><span class="term">11       B-tree, <acronym class="acronym">GiST</acronym> and <acronym class="acronym">SP-GiST</acronym> indexes12      </span></dt><dd><p>13        Short-term share/exclusive page-level locks are used for14        read/write access. Locks are released immediately after each15        index row is fetched or inserted.  These index types provide16        the highest concurrency without deadlock conditions.17       </p></dd><dt><span class="term">18       Hash indexes19      </span></dt><dd><p>20        Share/exclusive hash-bucket-level locks are used for read/write21        access.  Locks are released after the whole bucket is processed.22        Bucket-level locks provide better concurrency than index-level23        ones, but deadlock is possible since the locks are held longer24        than one index operation.25       </p></dd><dt><span class="term">26       <acronym class="acronym">GIN</acronym> indexes27      </span></dt><dd><p>28        Short-term share/exclusive page-level locks are used for29        read/write access. Locks are released immediately after each30        index row is fetched or inserted. But note that insertion of a31        GIN-indexed value usually produces several index key insertions32        per row, so GIN might do substantial work for a single value's33        insertion.34       </p></dd></dl></div><p>35   </p><p>36    Currently, B-tree indexes offer the best performance for concurrent37    applications; since they also have more features than hash38    indexes, they are the recommended index type for concurrent39    applications that need to index scalar data. When dealing with40    non-scalar data, B-trees are not useful, and GiST, SP-GiST or GIN41    indexes should be used instead.42   </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="mvcc-caveats.html" title="13.6. Caveats">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="mvcc.html" title="Chapter 13. Concurrency Control">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="performance-tips.html" title="Chapter 14. Performance Tips">Next</a></td></tr><tr><td width="40%" align="left" valign="top">13.6. Caveats </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="40%" align="right" valign="top"> Chapter 14. Performance Tips</td></tr></table></div></body></html>