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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 48. Logical Decoding</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="bgworker.html" title="Chapter 47. Background Worker Processes" /><link rel="next" href="logicaldecoding-example.html" title="48.1. Logical Decoding Examples" /></head><body id="docContent" class="container-fluid col-10"><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">Chapter 48. Logical Decoding</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="bgworker.html" title="Chapter 47. Background Worker Processes">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="server-programming.html" title="Part V. Server Programming">Up</a></td><th width="60%" align="center">Part V. Server Programming</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 13.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="logicaldecoding-example.html" title="48.1. Logical Decoding Examples">Next</a></td></tr></table><hr></hr></div><div class="chapter" id="LOGICALDECODING"><div class="titlepage"><div><div><h2 class="title">Chapter 48. Logical Decoding</h2></div></div></div><div class="toc"><p><strong>Table of Contents</strong></p><dl class="toc"><dt><span class="sect1"><a href="logicaldecoding-example.html">48.1. Logical Decoding Examples</a></span></dt><dt><span class="sect1"><a href="logicaldecoding-explanation.html">48.2. Logical Decoding Concepts</a></span></dt><dd><dl><dt><span class="sect2"><a href="logicaldecoding-explanation.html#id-1.8.14.8.2">48.2.1. Logical Decoding</a></span></dt><dt><span class="sect2"><a href="logicaldecoding-explanation.html#LOGICALDECODING-REPLICATION-SLOTS">48.2.2. Replication Slots</a></span></dt><dt><span class="sect2"><a href="logicaldecoding-explanation.html#id-1.8.14.8.4">48.2.3. Output Plugins</a></span></dt><dt><span class="sect2"><a href="logicaldecoding-explanation.html#id-1.8.14.8.5">48.2.4. Exported Snapshots</a></span></dt></dl></dd><dt><span class="sect1"><a href="logicaldecoding-walsender.html">48.3. Streaming Replication Protocol Interface</a></span></dt><dt><span class="sect1"><a href="logicaldecoding-sql.html">48.4. Logical Decoding <acronym class="acronym">SQL</acronym> Interface</a></span></dt><dt><span class="sect1"><a href="logicaldecoding-catalogs.html">48.5. System Catalogs Related to Logical Decoding</a></span></dt><dt><span class="sect1"><a href="logicaldecoding-output-plugin.html">48.6. Logical Decoding Output Plugins</a></span></dt><dd><dl><dt><span class="sect2"><a href="logicaldecoding-output-plugin.html#LOGICALDECODING-OUTPUT-INIT">48.6.1. Initialization Function</a></span></dt><dt><span class="sect2"><a href="logicaldecoding-output-plugin.html#LOGICALDECODING-CAPABILITIES">48.6.2. Capabilities</a></span></dt><dt><span class="sect2"><a href="logicaldecoding-output-plugin.html#LOGICALDECODING-OUTPUT-MODE">48.6.3. Output Modes</a></span></dt><dt><span class="sect2"><a href="logicaldecoding-output-plugin.html#LOGICALDECODING-OUTPUT-PLUGIN-CALLBACKS">48.6.4. Output Plugin Callbacks</a></span></dt><dt><span class="sect2"><a href="logicaldecoding-output-plugin.html#LOGICALDECODING-OUTPUT-PLUGIN-OUTPUT">48.6.5. Functions for Producing Output</a></span></dt></dl></dd><dt><span class="sect1"><a href="logicaldecoding-writer.html">48.7. Logical Decoding Output Writers</a></span></dt><dt><span class="sect1"><a href="logicaldecoding-synchronous.html">48.8. Synchronous Replication Support for Logical Decoding</a></span></dt><dd><dl><dt><span class="sect2"><a href="logicaldecoding-synchronous.html#id-1.8.14.14.2">48.8.1. Overview</a></span></dt><dt><span class="sect2"><a href="logicaldecoding-synchronous.html#LOGICALDECODING-SYNCHRONOUS-CAVEATS">48.8.2. Caveats</a></span></dt></dl></dd></dl></div><a id="id-1.8.14.2" class="indexterm"></a><p>
PostgreSQL provides infrastructure to stream the modifications performed
via SQL to external consumers. This functionality can be used for a
variety of purposes, including replication solutions and auditing.
</p><p>
Changes are sent out in streams identified by logical replication slots.
</p><p>
The format in which those changes are streamed is determined by the output
plugin used. An example plugin is provided in the PostgreSQL distribution.
Additional plugins can be
written to extend the choice of available formats without modifying any
core code.
Every output plugin has access to each individual new row produced
by <code class="command">INSERT</code> and the new row version created
by <code class="command">UPDATE</code>. Availability of old row versions for
<code class="command">UPDATE</code> and <code class="command">DELETE</code> depends on
the configured replica identity (see <a class="xref" href="sql-altertable.html#SQL-CREATETABLE-REPLICA-IDENTITY"><code class="literal">REPLICA IDENTITY</code></a>).
</p><p>
Changes can be consumed either using the streaming replication protocol
(see <a class="xref" href="protocol-replication.html" title="52.4. Streaming Replication Protocol">Section 52.4</a> and
<a class="xref" href="logicaldecoding-walsender.html" title="48.3. Streaming Replication Protocol Interface">Section 48.3</a>), or by calling functions
via SQL (see <a class="xref" href="logicaldecoding-sql.html" title="48.4. Logical Decoding SQL Interface">Section 48.4</a>). It is also possible
to write additional methods of consuming the output of a replication slot
without modifying core code
(see <a class="xref" href="logicaldecoding-writer.html" title="48.7. Logical Decoding Output Writers">Section 48.7</a>).
</p></div><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navfooter"><hr></hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="bgworker.html" title="Chapter 47. Background Worker Processes">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="server-programming.html" title="Part V. Server Programming">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="logicaldecoding-example.html" title="48.1. Logical Decoding Examples">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 47. Background Worker Processes </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 13.4 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 48.1. Logical Decoding Examples</td></tr></table></div></body></html>
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