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

Query Pattern

Index Type

Example

WHERE col = value

B-tree (default)

CREATE INDEX idx ON t (col)

WHERE col > value

B-tree

CREATE INDEX idx ON t (col)

WHERE a = x AND b > y

Composite

CREATE INDEX idx ON t (a, b)

WHERE jsonb @> '{}'

GIN

CREATE INDEX idx ON t USING gin (col)

WHERE tsv @@ query

GIN

CREATE INDEX idx ON t USING gin (col)

Time-series ranges

BRIN

CREATE INDEX idx ON t USING brin (col)

Data Type Quick Reference

Use Case

Correct Type

Avoid

IDs

bigint

int, random UUID

Strings

text

varchar(255)

Timestamps

timestamptz

timestamp

Money

numeric(10,2)

float

Flags

boolean

varchar, int

Common Patterns

Composite Index Order:

-- Equality columns first, then range columns

CREATE INDEX idx ON orders (status, created_at);

-- Works for: WHERE status = 'pending' AND created_at > '2024-01-01'

Covering Index:

CREATE INDEX idx ON users (email) INCLUDE (name, created_at);

-- Avoids table lookup for SELECT email, name, created_at

Partial Index:

CREATE INDEX idx ON users (email) WHERE deleted_at IS NULL;

-- Smaller index, only includes active users

RLS Policy (Optimized):

CREATE POLICY policy ON orders

  USING ((SELECT auth.uid()) = user_id);  -- Wrap in SELECT!

UPSERT:

INSERT INTO settings (user_id, key, value)

VALUES (123, 'theme', 'dark')

ON CONFLICT (user_id, key)

DO UPDATE SET value = EXCLUDED.value;

Cursor Pagination:

SELECT * FROM products WHERE id > $last_id ORDER BY id LIMIT 20;

-- O(1) vs OFFSET which is O(n)

Queue Processing:

UPDATE jobs SET status = 'processing'

WHERE id = (

  SELECT id FROM jobs WHERE status = 'pending'

  ORDER BY created_at LIMIT 1

  FOR UPDATE SKIP LOCKED

) RETURNING *;

Anti-Pattern Detection

-- Find unindexed foreign keys

SELECT conrelid::regclass, a.attname

FROM pg_constraint c

JOIN pg_attribute a ON a.attrelid = c.conrelid AND a.attnum = ANY(c.conkey)

WHERE c.contype = 'f'

  AND NOT EXISTS (

    SELECT 1 FROM pg_index i

    WHERE i.indrelid = c.conrelid AND a.attnum = ANY(i.indkey)

  );

-- Find slow queries

SELECT query, mean_exec_time, calls

FROM pg_stat_statements

WHERE mean_exec_time > 100

ORDER BY mean_exec_time DESC;

-- Check table bloat

SELECT relname, n_dead_tup, last_vacuum

FROM pg_stat_user_tables

WHERE n_dead_tup > 1000

ORDER BY n_dead_tup DESC;

Configuration Template

-- Connection limits (adjust for RAM)

ALTER SYSTEM SET max_connections = 100;

ALTER SYSTEM SET work_mem = '8MB';

-- Timeouts

ALTER SYSTEM SET idle_in_transaction_session_timeout = '30s';

ALTER SYSTEM SET statement_timeout = '30s';

-- Monitoring

CREATE EXTENSION IF NOT EXISTS pg_stat_statements;

-- Security defaults

REVOKE ALL ON SCHEMA public FROM public;

SELECT 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)