<?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>Chapter 53. Frontend/Backend 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="view-pg-views.html" title="52.93. pg_views" /><link rel="next" href="protocol-overview.html" title="53.1. Overview" /></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 53. Frontend/Backend Protocol</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="view-pg-views.html" title="52.93. pg_views">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="internals.html" title="Part VII. Internals">Up</a></td><th width="60%" align="center">Part VII. Internals</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 11.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="protocol-overview.html" title="53.1. Overview">Next</a></td></tr></table><hr></hr></div><div class="chapter" id="PROTOCOL"><div class="titlepage"><div><div><h2 class="title">Chapter 53. Frontend/Backend Protocol</h2></div></div></div><div class="toc"><p><strong>Table of Contents</strong></p><dl class="toc"><dt><span class="sect1"><a href="protocol-overview.html">53.1. Overview</a></span></dt><dd><dl><dt><span class="sect2"><a href="protocol-overview.html#PROTOCOL-MESSAGE-CONCEPTS">53.1.1. Messaging Overview</a></span></dt><dt><span class="sect2"><a href="protocol-overview.html#PROTOCOL-QUERY-CONCEPTS">53.1.2. Extended Query Overview</a></span></dt><dt><span class="sect2"><a href="protocol-overview.html#PROTOCOL-FORMAT-CODES">53.1.3. Formats and Format Codes</a></span></dt></dl></dd><dt><span class="sect1"><a href="protocol-flow.html">53.2. Message Flow</a></span></dt><dd><dl><dt><span class="sect2"><a href="protocol-flow.html#id-1.10.5.7.3">53.2.1. Start-up</a></span></dt><dt><span class="sect2"><a href="protocol-flow.html#id-1.10.5.7.4">53.2.2. Simple Query</a></span></dt><dt><span class="sect2"><a href="protocol-flow.html#PROTOCOL-FLOW-EXT-QUERY">53.2.3. Extended Query</a></span></dt><dt><span class="sect2"><a href="protocol-flow.html#id-1.10.5.7.6">53.2.4. Function Call</a></span></dt><dt><span class="sect2"><a href="protocol-flow.html#PROTOCOL-COPY">53.2.5. COPY Operations</a></span></dt><dt><span class="sect2"><a href="protocol-flow.html#PROTOCOL-ASYNC">53.2.6. Asynchronous Operations</a></span></dt><dt><span class="sect2"><a href="protocol-flow.html#id-1.10.5.7.9">53.2.7. Canceling Requests in Progress</a></span></dt><dt><span class="sect2"><a href="protocol-flow.html#id-1.10.5.7.10">53.2.8. Termination</a></span></dt><dt><span class="sect2"><a href="protocol-flow.html#id-1.10.5.7.11">53.2.9. <acronym class="acronym">SSL</acronym> Session Encryption</a></span></dt></dl></dd><dt><span class="sect1"><a href="sasl-authentication.html">53.3. SASL Authentication</a></span></dt><dd><dl><dt><span class="sect2"><a href="sasl-authentication.html#SASL-SCRAM-SHA-256">53.3.1. SCRAM-SHA-256 authentication</a></span></dt></dl></dd><dt><span class="sect1"><a href="protocol-replication.html">53.4. Streaming Replication Protocol</a></span></dt><dt><span class="sect1"><a href="protocol-logical-replication.html">53.5. Logical Streaming Replication Protocol</a></span></dt><dd><dl><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></dd><dt><span class="sect1"><a href="protocol-message-types.html">53.6. Message Data Types</a></span></dt><dt><span class="sect1"><a href="protocol-message-formats.html">53.7. Message Formats</a></span></dt><dt><span class="sect1"><a href="protocol-error-fields.html">53.8. Error and Notice Message Fields</a></span></dt><dt><span class="sect1"><a href="protocol-logicalrep-message-formats.html">53.9. Logical Replication Message Formats</a></span></dt><dt><span class="sect1"><a href="protocol-changes.html">53.10. Summary of Changes since Protocol 2.0</a></span></dt></dl></div><a id="id-1.10.5.2" class="indexterm"></a><p> <span class="productname">PostgreSQL</span> uses a message-based protocol for communication between frontends and backends (clients and servers). The protocol is supported over <acronym class="acronym">TCP/IP</acronym> and also over Unix-domain sockets. Port number 5432 has been registered with IANA as the customary TCP port number for servers supporting this protocol, but in practice any non-privileged port number can be used. </p><p> This document describes version 3.0 of the protocol, implemented in <span class="productname">PostgreSQL</span> 7.4 and later. For descriptions of the earlier protocol versions, see previous releases of the <span class="productname">PostgreSQL</span> documentation. A single server can support multiple protocol versions. The initial startup-request message tells the server which protocol version the client is attempting to use. If the major version requested by the client is not supported by the server, the connection will be rejected (for example, this would occur if the client requested protocol version 4.0, which does not exist as of this writing). If the minor version requested by the client is not supported by the server (e.g. the client requests version 3.1, but the server supports only 3.0), the server may either reject the connection or may respond with a NegotiateProtocolVersion message containing the highest minor protocol version which it supports. The client may then choose either to continue with the connection using the specified protocol version or to abort the connection. </p><p> In order to serve multiple clients efficiently, the server launches a new <span class="quote">“<span class="quote">backend</span>”</span> process for each client. In the current implementation, a new child process is created immediately after an incoming connection is detected. This is transparent to the protocol, however. For purposes of the protocol, the terms <span class="quote">“<span class="quote">backend</span>”</span> and <span class="quote">“<span class="quote">server</span>”</span> are interchangeable; likewise <span class="quote">“<span class="quote">frontend</span>”</span> and <span class="quote">“<span class="quote">client</span>”</span> are interchangeable. </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="view-pg-views.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="internals.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="protocol-overview.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">52.93. <code class="structname">pg_views</code> </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 53.1. Overview</td></tr></table></div></body></html>
