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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >Frontend/Backend Protocol</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK REV="MADE" HREF="mailto:pgsql-docs@postgresql.org"><LINK REL="HOME" TITLE="PostgreSQL 9.2.24 Documentation" HREF="index.html"><LINK REL="UP" TITLE="Internals" HREF="internals.html"><LINK REL="PREVIOUS" TITLE="pg_views" HREF="view-pg-views.html"><LINK REL="NEXT" TITLE="Overview" HREF="protocol-overview.html"><LINK REL="STYLESHEET" TYPE="text/css" HREF="stylesheet.css"><META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-8859-1"><META NAME="creation" CONTENT="2017-11-06T22:43:11"></HEAD ><BODY CLASS="CHAPTER" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="5" ALIGN="center" VALIGN="bottom" ><A HREF="index.html" >PostgreSQL 9.2.24 Documentation</A ></TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A TITLE="pg_views" HREF="view-pg-views.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="internals.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="60%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="20%" ALIGN="right" VALIGN="top" ><A TITLE="Overview" HREF="protocol-overview.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="CHAPTER" ><H1 ><A NAME="PROTOCOL" ></A >Chapter 46. Frontend/Backend Protocol</H1 ><DIV CLASS="TOC" ><DL ><DT ><B >Table of Contents</B ></DT ><DT >46.1. <A HREF="protocol-overview.html" >Overview</A ></DT ><DD ><DL ><DT >46.1.1. <A HREF="protocol-overview.html#PROTOCOL-MESSAGE-CONCEPTS" >Messaging Overview</A ></DT ><DT >46.1.2. <A HREF="protocol-overview.html#PROTOCOL-QUERY-CONCEPTS" >Extended Query Overview</A ></DT ><DT >46.1.3. <A HREF="protocol-overview.html#PROTOCOL-FORMAT-CODES" >Formats and Format Codes</A ></DT ></DL ></DD ><DT >46.2. <A HREF="protocol-flow.html" >Message Flow</A ></DT ><DD ><DL ><DT >46.2.1. <A HREF="protocol-flow.html#AEN95777" >Start-up</A ></DT ><DT >46.2.2. <A HREF="protocol-flow.html#AEN95852" >Simple Query</A ></DT ><DT >46.2.3. <A HREF="protocol-flow.html#PROTOCOL-FLOW-EXT-QUERY" >Extended Query</A ></DT ><DT >46.2.4. <A HREF="protocol-flow.html#AEN95963" >Function Call</A ></DT ><DT >46.2.5. <A HREF="protocol-flow.html#PROTOCOL-COPY" >COPY Operations</A ></DT ><DT >46.2.6. <A HREF="protocol-flow.html#PROTOCOL-ASYNC" >Asynchronous Operations</A ></DT ><DT >46.2.7. <A HREF="protocol-flow.html#AEN96049" >Canceling Requests in Progress</A ></DT ><DT >46.2.8. <A HREF="protocol-flow.html#AEN96057" >Termination</A ></DT ><DT >46.2.9. <A HREF="protocol-flow.html#AEN96066" ><ACRONYM CLASS="ACRONYM" >SSL</ACRONYM > Session Encryption</A ></DT ></DL ></DD ><DT >46.3. <A HREF="protocol-replication.html" >Streaming Replication Protocol</A ></DT ><DT >46.4. <A HREF="protocol-message-types.html" >Message Data Types</A ></DT ><DT >46.5. <A HREF="protocol-message-formats.html" >Message Formats</A ></DT ><DT >46.6. <A HREF="protocol-error-fields.html" >Error and Notice Message Fields</A ></DT ><DT >46.7. <A HREF="protocol-changes.html" >Summary of Changes since Protocol 2.0</A ></DT ></DL ></DIV ><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, and then the server follows that protocol if it is able. </P ><P > In order to serve multiple clients efficiently, the server launches a new <SPAN CLASS="QUOTE" >"backend"</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" >"backend"</SPAN > and <SPAN CLASS="QUOTE" >"server"</SPAN > are interchangeable; likewise <SPAN CLASS="QUOTE" >"frontend"</SPAN > and <SPAN CLASS="QUOTE" >"client"</SPAN > are interchangeable. </P ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="view-pg-views.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="protocol-overview.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><TT CLASS="STRUCTNAME" >pg_views</TT ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="internals.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Overview</TD ></TR ></TABLE ></DIV ></BODY ></HTML >