<?xml version="1.0" encoding="UTF-8" standalone="no"?> <!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>53.5. 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 Vsnapshot" /><link rel="prev" href="protocol-replication.html" title="53.4. Streaming Replication Protocol" /><link rel="next" href="protocol-message-types.html" title="53.6. Message Data Types" /></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">53.5. Logical Streaming Replication Protocol</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="protocol-replication.html" title="53.4. Streaming Replication Protocol">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="protocol.html" title="Chapter 53. Frontend/Backend Protocol">Up</a></td><th width="60%" align="center">Chapter 53. Frontend/Backend Protocol</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 11.12 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="protocol-message-types.html" title="53.6. 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">53.5. 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">53.5.1. Logical Streaming Replication Parameters</a></span></dt><dt><span class="sect2"><a href="protocol-logical-replication.html#PROTOCOL-LOGICAL-MESSAGES">53.5.2. Logical Replication Protocol Messages</a></span></dt><dt><span class="sect2"><a href="protocol-logical-replication.html#PROTOCOL-LOGICAL-MESSAGES-FLOW">53.5.3. 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">53.5.1. 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">53.5.2. 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="53.9. Logical Replication Message Formats">Section 53.9</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">53.5.3. 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="53.4. Streaming Replication Protocol">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="protocol.html" title="Chapter 53. Frontend/Backend Protocol">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="protocol-message-types.html" title="53.6. Message Data Types">Next</a></td></tr><tr><td width="40%" align="left" valign="top">53.4. Streaming Replication Protocol </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 11.12 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 53.6. Message Data Types</td></tr></table></div></body></html>