Postgres Patterns

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

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

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

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

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

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

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 *;

-- Find unindexed foreign keysSELECT conrelid::regclass, a.attnameFROM pg_constraint cJOIN 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 queriesSELECT query, mean_exec_time, callsFROM pg_stat_statementsWHERE mean_exec_time > 100ORDER BY mean_exec_time DESC;
-- Check table bloatSELECT relname, n_dead_tup, last_vacuumFROM pg_stat_user_tablesWHERE n_dead_tup > 1000ORDER BY n_dead_tup DESC;

-- Connection limits (adjust for RAM)ALTER SYSTEM SET max_connections = 100;ALTER SYSTEM SET work_mem = '8MB';
-- TimeoutsALTER SYSTEM SET idle_in_transaction_session_timeout = '30s';ALTER SYSTEM SET statement_timeout = '30s';
-- MonitoringCREATE EXTENSION IF NOT EXISTS pg_stat_statements;
-- Security defaultsREVOKE ALL ON SCHEMA public FROM public;
SELECT pg_reload_conf();