postgresql-best-practices

CREATE TABLE products (
    product_id SERIAL PRIMARY KEY,
    sku VARCHAR(50) NOT NULL UNIQUE,
    name TEXT NOT NULL,
    price NUMERIC(10, 2) NOT NULL CHECK (price >= 0),
    status VARCHAR(20) NOT NULL DEFAULT 'active'
        CHECK (status IN ('active', 'inactive', 'discontinued')),
    metadata JSONB DEFAULT '{}'
);

CREATE TABLE events (
    event_id BIGSERIAL,
    event_type VARCHAR(50) NOT NULL,
    payload JSONB,
    created_at TIMESTAMPTZ NOT NULL
) PARTITION BY RANGE (created_at);
 
CREATE TABLE events_2024_q1 PARTITION OF events
    FOR VALUES FROM ('2024-01-01') TO ('2024-04-01');

-- B-tree index for common lookups
CREATE INDEX idx_orders_customer ON orders(customer_id);
 
-- GIN index for JSONB queries
CREATE INDEX idx_orders_data ON orders USING GIN (order_data);
 
-- Partial index for active records only
CREATE INDEX idx_active_products ON products(name) WHERE status = 'active';
 
-- Covering index to avoid table lookup
CREATE INDEX idx_orders_covering ON orders(customer_id)
    INCLUDE (order_date, total_amount);

-- Check index usage
SELECT schemaname, relname, indexrelname, idx_scan, idx_tup_read
FROM pg_stat_user_indexes
ORDER BY idx_scan ASC;

EXPLAIN (ANALYZE, BUFFERS, FORMAT TEXT)
SELECT c.name, COUNT(o.order_id)
FROM customers c
LEFT JOIN orders o ON c.customer_id = o.customer_id
WHERE c.created_at > '2024-01-01'
GROUP BY c.customer_id, c.name;

WITH recent_orders AS MATERIALIZED (
    SELECT customer_id, COUNT(*) AS order_count, SUM(total) AS total_spent
    FROM orders
    WHERE order_date > CURRENT_DATE - INTERVAL '30 days'
    GROUP BY customer_id
)
SELECT c.name, ro.order_count, ro.total_spent
FROM customers c
JOIN recent_orders ro ON c.customer_id = ro.customer_id
WHERE ro.total_spent > 1000;

SELECT
    order_id,
    customer_id,
    total_amount,
    SUM(total_amount) OVER (PARTITION BY customer_id ORDER BY order_date) AS running_total,
    ROW_NUMBER() OVER (PARTITION BY customer_id ORDER BY order_date DESC) AS order_rank
FROM orders;

-- Efficient JSONB query with GIN index
SELECT * FROM products
WHERE metadata @> '{"category": "electronics"}';
 
-- Extract specific fields
SELECT
    product_id,
    metadata->>'brand' AS brand,
    (metadata->>'rating')::numeric AS rating
FROM products
WHERE metadata ? 'rating';

-- Recommended session settings
SET statement_timeout = '30s';
SET lock_timeout = '10s';
SET idle_in_transaction_session_timeout = '60s';

-- Use advisory locks for application coordination
SELECT pg_advisory_lock(hashtext('resource_name'));
-- Do work
SELECT pg_advisory_unlock(hashtext('resource_name'));
 
-- Check for blocking queries
SELECT blocked_locks.pid AS blocked_pid,
       blocking_locks.pid AS blocking_pid,
       blocked_activity.query AS blocked_query
FROM pg_catalog.pg_locks blocked_locks
JOIN pg_catalog.pg_locks blocking_locks
    ON blocking_locks.locktype = blocked_locks.locktype
    AND blocking_locks.relation = blocked_locks.relation
    AND blocking_locks.pid != blocked_locks.pid
JOIN pg_catalog.pg_stat_activity blocked_activity
    ON blocked_activity.pid = blocked_locks.pid;

-- Check table bloat
SELECT schemaname, relname,
       n_live_tup, n_dead_tup,
       round(n_dead_tup * 100.0 / nullif(n_live_tup + n_dead_tup, 0), 2) AS dead_pct
FROM pg_stat_user_tables
WHERE n_dead_tup > 1000
ORDER BY n_dead_tup DESC;

-- Enable row-level security
ALTER TABLE documents ENABLE ROW LEVEL SECURITY;
 
CREATE POLICY documents_tenant_policy ON documents
    FOR ALL
    USING (tenant_id = current_setting('app.tenant_id')::uuid);
 
-- Grant minimal privileges
GRANT SELECT, INSERT, UPDATE ON orders TO app_user;
GRANT USAGE ON SEQUENCE orders_order_id_seq TO app_user;

-- Enable pg_stat_statements
CREATE EXTENSION IF NOT EXISTS pg_stat_statements;
 
-- Find slow queries
SELECT query, calls, mean_exec_time, total_exec_time
FROM pg_stat_statements
ORDER BY mean_exec_time DESC
LIMIT 10;