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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>13.6. 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 V1.79.1" /><link rel="prev" href="mvcc-caveats.html" title="13.5. Caveats" /><link rel="next" href="performance-tips.html" title="Chapter 14. Performance Tips" /></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">13.6. Locking and Indexes</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="mvcc-caveats.html" title="13.5. 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 12.4 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></hr></div><div class="sect1" id="LOCKING-INDEXES"><div class="titlepage"><div><div><h2 class="title" style="clear: both">13.6. Locking and Indexes</h2></div></div></div><a id="id-1.5.12.9.2" class="indexterm"></a><p>
- Though <span class="productname">PostgreSQL</span>
- provides nonblocking read/write access to table
- data, nonblocking read/write access is not currently offered for every
- index access method implemented
- in <span class="productname">PostgreSQL</span>.
- The various index types are handled as follows:
-
- </p><div class="variablelist"><dl class="variablelist"><dt><span class="term">
- B-tree, <acronym class="acronym">GiST</acronym> and <acronym class="acronym">SP-GiST</acronym> indexes
- </span></dt><dd><p>
- Short-term share/exclusive page-level locks are used for
- read/write access. Locks are released immediately after each
- index row is fetched or inserted. These index types provide
- the highest concurrency without deadlock conditions.
- </p></dd><dt><span class="term">
- Hash indexes
- </span></dt><dd><p>
- Share/exclusive hash-bucket-level locks are used for read/write
- access. Locks are released after the whole bucket is processed.
- Bucket-level locks provide better concurrency than index-level
- ones, but deadlock is possible since the locks are held longer
- than one index operation.
- </p></dd><dt><span class="term">
- <acronym class="acronym">GIN</acronym> indexes
- </span></dt><dd><p>
- Short-term share/exclusive page-level locks are used for
- read/write access. Locks are released immediately after each
- index row is fetched or inserted. But note that insertion of a
- GIN-indexed value usually produces several index key insertions
- per row, so GIN might do substantial work for a single value's
- insertion.
- </p></dd></dl></div><p>
- </p><p>
- Currently, B-tree indexes offer the best performance for concurrent
- applications; since they also have more features than hash
- indexes, they are the recommended index type for concurrent
- applications that need to index scalar data. When dealing with
- non-scalar data, B-trees are not useful, and GiST, SP-GiST or GIN
- indexes should be used instead.
- </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">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="mvcc.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="performance-tips.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">13.5. Caveats </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 14. Performance Tips</td></tr></table></div></body></html>
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