qos

Overview

requires shared_preload_libraries = ‘qos’; official support PG15+

Version

Build

You can build the RPM / DEB packages for pg_qos using pig build:

pig build pkg pg_qos         # build RPM / DEB packages

Install

You can install pg_qos directly. First, make sure the PGDG and PIGSTY repositories are added and enabled:

pig repo add pgsql -u          # Add repo and update cache

Install the extension using pig or apt/yum/dnf:

pig install pg_qos;          # Install for current active PG version

pig ext install -y pg_qos -v 18  # PG 18
pig ext install -y pg_qos -v 17  # PG 17
pig ext install -y pg_qos -v 16  # PG 16
pig ext install -y pg_qos -v 15  # PG 15

dnf install -y pg_qos_18       # PG 18
dnf install -y pg_qos_17       # PG 17
dnf install -y pg_qos_16       # PG 16
dnf install -y pg_qos_15       # PG 15

apt install -y postgresql-18-qos   # PG 18
apt install -y postgresql-17-qos   # PG 17
apt install -y postgresql-16-qos   # PG 16
apt install -y postgresql-15-qos   # PG 15

Preload:

shared_preload_libraries = 'qos';

Create Extension:

CREATE EXTENSION qos;

Usage

qos: QoS resource governor extension for PostgreSQL sessions and queries

The qos extension provides Quality of Service resource governance for PostgreSQL, allowing administrators to set per-role and per-database limits on memory usage, CPU cores, and concurrent transactions/statements.

Configuration Parameters

Per-Role Limits

ALTER ROLE app_user SET qos.work_mem_limit = '32MB';
ALTER ROLE app_user SET qos.cpu_core_limit = '2';
ALTER ROLE app_user SET qos.max_concurrent_select = '100';

Per-Database Limits

ALTER DATABASE appdb SET qos.max_concurrent_tx = '200';

Combined Role + Database Limits

ALTER ROLE app_user IN DATABASE appdb SET qos.work_mem_limit = '4MB';
ALTER ROLE app_user IN DATABASE appdb SET qos.max_concurrent_update = '10';

Enforcement Behavior

• Work memory: Intercepts SET work_mem and rejects values exceeding configured limits
• CPU limiting (Linux only): Binds backend to N CPU cores via CPU affinity; on non-Linux platforms, limits parallel workers instead
• Concurrency: Executor hooks track active transactions/statements by type; violations block execution

Observability

SET client_min_messages = 'debug1';  -- enable debug output for QoS events

The most restrictive combination of role-level and database-level settings takes effect. Requires shared_preload_libraries = 'qos' and PostgreSQL 15+.