PostgreSQL Patterns

Quick reference for PostgreSQL best practices. For detailed guidance, use the database-reviewer agent.

When to Activate

• Writing SQL queries or migrations
• Designing database schemas
• Troubleshooting slow queries
• Implementing Row Level Security
• Setting up connection pooling

Quick Reference

Index Cheat Sheet

Data Type Quick Reference

Common Patterns

Composite Index Order:

sql
1-- Equality columns first, then range columns
2CREATE INDEX idx ON orders (status, created_at);
3-- Works for: WHERE status = 'pending' AND created_at > '2024-01-01'

Covering Index:

sql
1CREATE INDEX idx ON users (email) INCLUDE (name, created_at);
2-- Avoids table lookup for SELECT email, name, created_at

Partial Index:

sql
1CREATE INDEX idx ON users (email) WHERE deleted_at IS NULL;
2-- Smaller index, only includes active users

RLS Policy (Optimized):

sql
1CREATE POLICY policy ON orders
2  USING ((SELECT auth.uid()) = user_id);  -- Wrap in SELECT!

UPSERT:

sql
1INSERT INTO settings (user_id, key, value)
2VALUES (123, 'theme', 'dark')
3ON CONFLICT (user_id, key)
4DO UPDATE SET value = EXCLUDED.value;

Cursor Pagination:

sql
1SELECT * FROM products WHERE id > $last_id ORDER BY id LIMIT 20;
2-- O(1) vs OFFSET which is O(n)

Queue Processing:

sql
1UPDATE jobs SET status = 'processing'
2WHERE id = (
3  SELECT id FROM jobs WHERE status = 'pending'
4  ORDER BY created_at LIMIT 1
5  FOR UPDATE SKIP LOCKED
6) RETURNING *;

Anti-Pattern Detection

sql
1-- Find unindexed foreign keys
2SELECT conrelid::regclass, a.attname
3FROM pg_constraint c
4JOIN pg_attribute a ON a.attrelid = c.conrelid AND a.attnum = ANY(c.conkey)
5WHERE c.contype = 'f'
6  AND NOT EXISTS (
7    SELECT 1 FROM pg_index i
8    WHERE i.indrelid = c.conrelid AND a.attnum = ANY(i.indkey)
9  );
10
11-- Find slow queries
12SELECT query, mean_exec_time, calls
13FROM pg_stat_statements
14WHERE mean_exec_time > 100
15ORDER BY mean_exec_time DESC;
16
17-- Check table bloat
18SELECT relname, n_dead_tup, last_vacuum
19FROM pg_stat_user_tables
20WHERE n_dead_tup > 1000
21ORDER BY n_dead_tup DESC;

Configuration Template

sql
1-- Connection limits (adjust for RAM)
2ALTER SYSTEM SET max_connections = 100;
3ALTER SYSTEM SET work_mem = '8MB';
4
5-- Timeouts
6ALTER SYSTEM SET idle_in_transaction_session_timeout = '30s';
7ALTER SYSTEM SET statement_timeout = '30s';
8
9-- Monitoring
10CREATE EXTENSION IF NOT EXISTS pg_stat_statements;
11
12-- Security defaults
13REVOKE ALL ON SCHEMA public FROM public;
14
15SELECT pg_reload_conf();

Related

• Agent: database-reviewer - Full database review workflow
• Skill: clickhouse-io - ClickHouse analytics patterns
• Skill: backend-patterns - API and backend patterns

Based on Supabase Agent Skills (credit: Supabase team) (MIT License)