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Green_GoodERP18_FSJ_Standard/PostgreSQL/doc/postgresql/html/protocol-logical-replicatio...

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  1. <?xml version="1.0" encoding="UTF-8" standalone="no"?>

  2. <!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><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 12.4 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>

  3.   This section describes the logical replication protocol, which is the message

  4.   flow started by the <code class="literal">START_REPLICATION</code>

  5.   <code class="literal">SLOT</code> <em class="replaceable"><code>slot_name</code></em>

  6.   <code class="literal">LOGICAL</code> replication command.

  7.  </p><p>

  8.   The logical streaming replication protocol builds on the primitives of

  9.   the physical streaming replication protocol.

  10.  </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>

  11.    The logical replication <code class="literal">START_REPLICATION</code> command

  12.    accepts following parameters:

  13. 

  14.    </p><div class="variablelist"><dl class="variablelist"><dt><span class="term">

  15.       proto_version

  16.      </span></dt><dd><p>

  17.        Protocol version. Currently only version <code class="literal">1</code> is

  18.        supported.

  19.       </p></dd><dt><span class="term">

  20.       publication_names

  21.      </span></dt><dd><p>

  22.        Comma separated list of publication names for which to subscribe

  23.        (receive changes). The individual publication names are treated

  24.        as standard objects names and can be quoted the same as needed.

  25.       </p></dd></dl></div><p>

  26. 

  27.   </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>

  28.    The individual protocol messages are discussed in the following

  29.    subsections. Individual messages are described in

  30.    <a class="xref" href="protocol-logicalrep-message-formats.html" title="52.9. Logical Replication Message Formats">Section 52.9</a>.

  31.   </p><p>

  32.    All top-level protocol messages begin with a message type byte.

  33.    While represented in code as a character, this is a signed byte with no

  34.    associated encoding.

  35.   </p><p>

  36.    Since the streaming replication protocol supplies a message length there

  37.    is no need for top-level protocol messages to embed a length in their

  38.    header.

  39.   </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>

  40.    With the exception of the <code class="literal">START_REPLICATION</code> command and

  41.    the replay progress messages, all information flows only from the backend

  42.    to the frontend.

  43.   </p><p>

  44.    The logical replication protocol sends individual transactions one by one.

  45.    This means that all messages between a pair of Begin and Commit messages

  46.    belong to the same transaction.

  47.   </p><p>

  48.    Every sent transaction contains zero or more DML messages (Insert,

  49.    Update, Delete). In case of a cascaded setup it can also contain Origin

  50.    messages. The origin message indicated that the transaction originated on

  51.    different replication node. Since a replication node in the scope of logical

  52.    replication protocol can be pretty much anything, the only identifier

  53.    is the origin name. It's downstream's responsibility to handle this as

  54.    needed (if needed). The Origin message is always sent before any DML

  55.    messages in the transaction.

  56.   </p><p>

  57.    Every DML message contains an arbitrary relation ID, which can be mapped to

  58.    an ID in the Relation messages. The Relation messages describe the schema of the

  59.    given relation. The Relation message is sent for a given relation either

  60.    because it is the first time we send a DML message for given relation in the

  61.    current session or because the relation definition has changed since the

  62.    last Relation message was sent for it. The protocol assumes that the client

  63.    is capable of caching the metadata for as many relations as needed.

  64.   </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">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="protocol.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="protocol-message-types.html">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">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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