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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>55.5. 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="55.4. Streaming Replication Protocol" /><link rel="next" href="protocol-message-types.html" title="55.6. Message Data Types" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">55.5. Logical Streaming Replication Protocol</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="protocol-replication.html" title="55.4. Streaming Replication Protocol">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="protocol.html" title="Chapter 55. Frontend/Backend Protocol">Up</a></td><th width="60%" align="center">Chapter 55. Frontend/Backend Protocol</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 15.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="protocol-message-types.html" title="55.6. Message Data Types">Next</a></td></tr></table><hr /></div><div class="sect1" id="PROTOCOL-LOGICAL-REPLICATION"><div class="titlepage"><div><div><h2 class="title" style="clear: both">55.5. 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">55.5.1. Logical Streaming Replication Parameters</a></span></dt><dt><span class="sect2"><a href="protocol-logical-replication.html#PROTOCOL-LOGICAL-MESSAGES">55.5.2. Logical Replication Protocol Messages</a></span></dt><dt><span class="sect2"><a href="protocol-logical-replication.html#PROTOCOL-LOGICAL-MESSAGES-FLOW">55.5.3. 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">55.5.1. 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 versions <code class="literal">1</code>, <code class="literal">2</code>,
       and <code class="literal">3</code> are supported.
      </p><p>
       Version <code class="literal">2</code> is supported only for server version 14
       and above, and it allows streaming of large in-progress transactions.
      </p><p>
       Version <code class="literal">3</code> is supported only for server version 15
       and above, and it allows streaming of two-phase commits.
      </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">55.5.2. 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="55.9. Logical Replication Message Formats">Section 55.9</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">55.5.3. 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. Similarly, all messages between a pair of
   Begin Prepare and Prepare messages belong to the same transaction.
   It also sends changes of large in-progress transactions between a pair of
   Stream Start and Stream Stop messages. The last stream of such a transaction
   contains a Stream Commit or Stream Abort message.
  </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 a relation OID, identifying the publisher's
   relation that was acted on.  Before the first DML message for a given
   relation OID, a Relation message will be sent, describing the schema of
   that relation.  Subsequently, a new Relation message will be sent if
   the relation's definition has changed since the last Relation message
   was sent for it.  (The protocol assumes that the client is capable of
   remembering this metadata for as many relations as needed.)
  </p><p>
   Relation messages identify column types by their OIDs.  In the case
   of a built-in type, it is assumed that the client can look up that
   type OID locally, so no additional data is needed.  For a non-built-in
   type OID, a Type message will be sent before the Relation message,
   to provide the type name associated with that OID.  Thus, a client that
   needs to specifically identify the types of relation columns should
   cache the contents of Type messages, and first consult that cache to
   see if the type OID is defined there.  If not, look up the type OID
   locally.
  </p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="protocol-replication.html" title="55.4. Streaming Replication Protocol">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="protocol.html" title="Chapter 55. Frontend/Backend Protocol">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="protocol-message-types.html" title="55.6. Message Data Types">Next</a></td></tr><tr><td width="40%" align="left" valign="top">55.4. Streaming Replication Protocol </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 15.5 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 55.6. Message Data Types</td></tr></table></div></body></html>