Chapter 55. Frontend/Backend Protocol

Chapter 55. Frontend/Backend Protocol
Prev	Up	Part VII. Internals	Home	Next

Table of Contents

55.1. Overview

55.1.1. Messaging Overview
55.1.2. Extended Query Overview
55.1.3. Formats and Format Codes

55.2. Message Flow

55.2.1. Start-up
55.2.2. Simple Query
55.2.3. Extended Query
55.2.4. Pipelining
55.2.5. Function Call
55.2.6. COPY Operations
55.2.7. Asynchronous Operations
55.2.8. Canceling Requests in Progress
55.2.9. Termination
55.2.10. SSL Session Encryption
55.2.11. GSSAPI Session Encryption

55.3. SASL Authentication

55.3.1. SCRAM-SHA-256 Authentication

55.4. Streaming Replication Protocol

55.5. Logical Streaming Replication Protocol

55.5.1. Logical Streaming Replication Parameters
55.5.2. Logical Replication Protocol Messages
55.5.3. Logical Replication Protocol Message Flow

55.6. Message Data Types

55.7. Message Formats

55.8. Error and Notice Message Fields

55.9. Logical Replication Message Formats

55.10. 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 3.0 of the protocol, implemented in + PostgreSQL 7.4 and later. For descriptions + of the earlier protocol versions, see previous releases of the + PostgreSQL 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. +

+ 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. +

Prev	Up	Next
54.35. `pg_views`	Home	55.1. Overview