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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>52.5. Logical Streaming Replication Protocol</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="protocol-replication.html" title="52.4. Streaming Replication Protocol" /><link rel="next" href="protocol-message-types.html" title="52.6. Message Data Types" /></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">52.5. Logical Streaming Replication Protocol</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="protocol-replication.html" title="52.4. Streaming Replication Protocol">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="protocol.html" title="Chapter 52. Frontend/Backend Protocol">Up</a></td><th width="60%" align="center">Chapter 52. Frontend/Backend Protocol</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="protocol-message-types.html" title="52.6. Message Data Types">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="PROTOCOL-LOGICAL-REPLICATION"><div class="titlepage"><div><div><h2 class="title" style="clear: both">52.5. Logical Streaming Replication Protocol</h2></div></div></div><div class="toc"><dl class="toc"><dt><span class="sect2"><a href="protocol-logical-replication.html#PROTOCOL-LOGICAL-REPLICATION-PARAMS">52.5.1. Logical Streaming Replication Parameters</a></span></dt><dt><span class="sect2"><a href="protocol-logical-replication.html#PROTOCOL-LOGICAL-MESSAGES">52.5.2. Logical Replication Protocol Messages</a></span></dt><dt><span class="sect2"><a href="protocol-logical-replication.html#PROTOCOL-LOGICAL-MESSAGES-FLOW">52.5.3. Logical Replication Protocol Message Flow</a></span></dt></dl></div><p>
This section describes the logical replication protocol, which is the message
flow started by the <code class="literal">START_REPLICATION</code>
<code class="literal">SLOT</code> <em class="replaceable"><code>slot_name</code></em>
<code class="literal">LOGICAL</code> replication command.
</p><p>
The logical streaming replication protocol builds on the primitives of
the physical streaming replication protocol.
</p><div class="sect2" id="PROTOCOL-LOGICAL-REPLICATION-PARAMS"><div class="titlepage"><div><div><h3 class="title">52.5.1. Logical Streaming Replication Parameters</h3></div></div></div><p>
The logical replication <code class="literal">START_REPLICATION</code> command
accepts following parameters:
</p><div class="variablelist"><dl class="variablelist"><dt><span class="term">
proto_version
</span></dt><dd><p>
Protocol version. Currently only version <code class="literal">1</code> is
supported.
</p></dd><dt><span class="term">
publication_names
</span></dt><dd><p>
Comma separated list of publication names for which to subscribe
(receive changes). The individual publication names are treated
as standard objects names and can be quoted the same as needed.
</p></dd></dl></div><p>
</p></div><div class="sect2" id="PROTOCOL-LOGICAL-MESSAGES"><div class="titlepage"><div><div><h3 class="title">52.5.2. Logical Replication Protocol Messages</h3></div></div></div><p>
The individual protocol messages are discussed in the following
subsections. Individual messages are described in
<a class="xref" href="protocol-logicalrep-message-formats.html" title="52.9. Logical Replication Message Formats">Section 52.9</a>.
</p><p>
All top-level protocol messages begin with a message type byte.
While represented in code as a character, this is a signed byte with no
associated encoding.
</p><p>
Since the streaming replication protocol supplies a message length there
is no need for top-level protocol messages to embed a length in their
header.
</p></div><div class="sect2" id="PROTOCOL-LOGICAL-MESSAGES-FLOW"><div class="titlepage"><div><div><h3 class="title">52.5.3. Logical Replication Protocol Message Flow</h3></div></div></div><p>
With the exception of the <code class="literal">START_REPLICATION</code> command and
the replay progress messages, all information flows only from the backend
to the frontend.
</p><p>
The logical replication protocol sends individual transactions one by one.
This means that all messages between a pair of Begin and Commit messages
belong to the same transaction.
</p><p>
Every sent transaction contains zero or more DML messages (Insert,
Update, Delete). In case of a cascaded setup it can also contain Origin
messages. The origin message indicates that the transaction originated on
different replication node. Since a replication node in the scope of logical
replication protocol can be pretty much anything, the only identifier
is the origin name. It's downstream's responsibility to handle this as
needed (if needed). The Origin message is always sent before any DML
messages in the transaction.
</p><p>
Every DML message contains an arbitrary relation ID, which can be mapped to
an ID in the Relation messages. The Relation messages describe the schema of the
given relation. The Relation message is sent for a given relation either
because it is the first time we send a DML message for given relation in the
current session or because the relation definition has changed since the
last Relation message was sent for it. The protocol assumes that the client
is capable of caching the metadata for as many relations as needed.
</p></div></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="protocol-replication.html" title="52.4. Streaming Replication Protocol">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="protocol.html" title="Chapter 52. Frontend/Backend Protocol">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="protocol-message-types.html" title="52.6. Message Data Types">Next</a></td></tr><tr><td width="40%" align="left" valign="top">52.4. Streaming Replication Protocol </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"> 52.6. Message Data Types</td></tr></table></div></body></html>
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