Chapter 54. Frontend/Backend Protocol

   Table of Contents

   54.1. Overview

        54.1.1. Messaging Overview
        54.1.2. Extended Query Overview
        54.1.3. Formats and Format Codes
        54.1.4. Protocol Versions

   54.2. Message Flow

        54.2.1. Start-up
        54.2.2. Simple Query
        54.2.3. Extended Query
        54.2.4. Pipelining
        54.2.5. Function Call
        54.2.6. COPY Operations
        54.2.7. Asynchronous Operations
        54.2.8. Canceling Requests in Progress
        54.2.9. Termination
        54.2.10. SSL Session Encryption
        54.2.11. GSSAPI Session Encryption

   54.3. SASL Authentication

        54.3.1. SCRAM-SHA-256 Authentication
        54.3.2. OAUTHBEARER Authentication

   54.4. Streaming Replication Protocol
   54.5. Logical Streaming Replication Protocol

        54.5.1. Logical Streaming Replication Parameters
        54.5.2. Logical Replication Protocol Messages
        54.5.3. Logical Replication Protocol Message Flow

   54.6. Message Data Types
   54.7. Message Formats
   54.8. Error and Notice Message Fields
   54.9. Logical Replication Message Formats
   54.10. Summary of Changes since Protocol 2.0

   PostgreSQL uses a message-based protocol for communication between
   frontends and backends (clients and servers). The protocol is supported
   over TCP/IP 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.

   This document describes version 3.2 of the protocol, introduced in
   PostgreSQL version 18. The server and the libpq client library are
   backwards compatible with protocol version 3.0, implemented in
   PostgreSQL 7.4 and later.

   In order to serve multiple clients efficiently, the server launches a
   new “backend” 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 “backend” and “server” are interchangeable;
   likewise “frontend” and “client” are interchangeable.