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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 30. Logical Replication</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="wal-internals.html" title="29.5. WAL Internals" /><link rel="next" href="logical-replication-publication.html" title="30.1. Publication" /></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 30. Logical Replication</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="wal-internals.html" title="29.5. WAL Internals">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="admin.html" title="Part III. Server Administration">Up</a></td><th width="60%" align="center">Part III. Server Administration</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="logical-replication-publication.html" title="30.1. Publication">Next</a></td></tr></table><hr></hr></div><div class="chapter" id="LOGICAL-REPLICATION"><div class="titlepage"><div><div><h2 class="title">Chapter 30. Logical Replication</h2></div></div></div><div class="toc"><p><strong>Table of Contents</strong></p><dl class="toc"><dt><span class="sect1"><a href="logical-replication-publication.html">30.1. Publication</a></span></dt><dt><span class="sect1"><a href="logical-replication-subscription.html">30.2. Subscription</a></span></dt><dd><dl><dt><span class="sect2"><a href="logical-replication-subscription.html#LOGICAL-REPLICATION-SUBSCRIPTION-SLOT">30.2.1. Replication Slot Management</a></span></dt></dl></dd><dt><span class="sect1"><a href="logical-replication-conflicts.html">30.3. Conflicts</a></span></dt><dt><span class="sect1"><a href="logical-replication-restrictions.html">30.4. Restrictions</a></span></dt><dt><span class="sect1"><a href="logical-replication-architecture.html">30.5. Architecture</a></span></dt><dd><dl><dt><span class="sect2"><a href="logical-replication-architecture.html#LOGICAL-REPLICATION-SNAPSHOT">30.5.1. Initial Snapshot</a></span></dt></dl></dd><dt><span class="sect1"><a href="logical-replication-monitoring.html">30.6. Monitoring</a></span></dt><dt><span class="sect1"><a href="logical-replication-security.html">30.7. Security</a></span></dt><dt><span class="sect1"><a href="logical-replication-config.html">30.8. Configuration Settings</a></span></dt><dt><span class="sect1"><a href="logical-replication-quick-setup.html">30.9. Quick Setup</a></span></dt></dl></div><p>
- Logical replication is a method of replicating data objects and their
- changes, based upon their replication identity (usually a primary key). We
- use the term logical in contrast to physical replication, which uses exact
- block addresses and byte-by-byte replication. PostgreSQL supports both
- mechanisms concurrently, see <a class="xref" href="high-availability.html" title="Chapter 26. High Availability, Load Balancing, and Replication">Chapter 26</a>. Logical
- replication allows fine-grained control over both data replication and
- security.
- </p><p>
- Logical replication uses a <em class="firstterm">publish</em>
- and <em class="firstterm">subscribe</em> model with one or
- more <em class="firstterm">subscribers</em> subscribing to one or more
- <em class="firstterm">publications</em> on a <em class="firstterm">publisher</em>
- node. Subscribers pull data from the publications they subscribe to and may
- subsequently re-publish data to allow cascading replication or more complex
- configurations.
- </p><p>
- Logical replication of a table typically starts with taking a snapshot
- of the data on the publisher database and copying that to the subscriber.
- Once that is done, the changes on the publisher are sent to the subscriber
- as they occur in real-time. The subscriber applies the data in the same
- order as the publisher so that transactional consistency is guaranteed for
- publications within a single subscription. This method of data replication
- is sometimes referred to as transactional replication.
- </p><p>
- The typical use-cases for logical replication are:
-
- </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
- Sending incremental changes in a single database or a subset of a
- database to subscribers as they occur.
- </p></li><li class="listitem"><p>
- Firing triggers for individual changes as they arrive on the
- subscriber.
- </p></li><li class="listitem"><p>
- Consolidating multiple databases into a single one (for example for
- analytical purposes).
- </p></li><li class="listitem"><p>
- Replicating between different major versions of PostgreSQL.
- </p></li><li class="listitem"><p>
- Replicating between PostgreSQL instances on different platforms (for
- example Linux to Windows)
- </p></li><li class="listitem"><p>
- Giving access to replicated data to different groups of users.
- </p></li><li class="listitem"><p>
- Sharing a subset of the database between multiple databases.
- </p></li></ul></div><p>
- </p><p>
- The subscriber database behaves in the same way as any other PostgreSQL
- instance and can be used as a publisher for other databases by defining its
- own publications. When the subscriber is treated as read-only by
- application, there will be no conflicts from a single subscription. On the
- other hand, if there are other writes done either by an application or by other
- subscribers to the same set of tables, conflicts can arise.
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