/postgres-patterns

name: postgres-patterns
description: PostgreSQL database patterns for query optimization, schema design, indexing, and security. Based on Supabase best practices. Use when designing PostgreSQL schemas, indexes, or RLS policies, or when a query is too slow.
metadata:
  origin: ECC

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

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