qos

pg_qos : QoS resource governor extension for PostgreSQL sessions and queries

Overview

Packages

Source

pig build pkg pg_qos;		# build rpm/deb

Install

Make sure PGDG and PIGSTY repo available:

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

Install this extension with pig:

pig install pg_qos;		# install via package name, for the active PG version
pig install qos;		# install by extension name, for the current active PG version

pig install qos -v 18;   # install for PG 18
pig install qos -v 17;   # install for PG 17
pig install qos -v 16;   # install for PG 16
pig install qos -v 15;   # install for PG 15

Config this extension to shared_preload_libraries:

shared_preload_libraries = 'qos';

Create this extension with:

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+.