postgresql-optimization

-- PostgreSQL arrays
CREATE TABLE posts (
    id SERIAL PRIMARY KEY,
    tags TEXT[],
    categories INTEGER[]
);
 
-- Array queries and operations
SELECT * FROM posts WHERE 'postgresql' = ANY(tags);
SELECT * FROM posts WHERE tags && ARRAY['database', 'sql'];
SELECT * FROM posts WHERE array_length(tags, 1) > 3;
 
-- Array aggregation
SELECT array_agg(DISTINCT category) FROM posts, unnest(categories) as category;

-- Advanced window functions
SELECT 
    product_id,
    sale_date,
    amount,
    -- Running totals
    SUM(amount) OVER (PARTITION BY product_id ORDER BY sale_date) as running_total,
    -- Moving averages
    AVG(amount) OVER (PARTITION BY product_id ORDER BY sale_date ROWS BETWEEN 2 PRECEDING AND CURRENT ROW) as moving_avg,
    -- Rankings
    DENSE_RANK() OVER (PARTITION BY EXTRACT(month FROM sale_date) ORDER BY amount DESC) as monthly_rank,
    -- Lag/Lead for comparisons
    LAG(amount, 1) OVER (PARTITION BY product_id ORDER BY sale_date) as prev_amount
FROM sales;

-- PostgreSQL full-text search
CREATE TABLE documents (
    id SERIAL PRIMARY KEY,
    title TEXT,
    content TEXT,
    search_vector tsvector
);
 
-- Update search vector
UPDATE documents 
SET search_vector = to_tsvector('english', title || ' ' || content);
 
-- GIN index for search performance
CREATE INDEX idx_documents_search ON documents USING gin(search_vector);
 
-- Search queries
SELECT * FROM documents 
WHERE search_vector @@ plainto_tsquery('english', 'postgresql database');
 
-- Ranking results
SELECT *, ts_rank(search_vector, plainto_tsquery('postgresql')) as rank
FROM documents 
WHERE search_vector @@ plainto_tsquery('postgresql')
ORDER BY rank DESC;

-- EXPLAIN ANALYZE for performance analysis
EXPLAIN (ANALYZE, BUFFERS, FORMAT TEXT) 
SELECT u.name, COUNT(o.id) as order_count
FROM users u
LEFT JOIN orders o ON u.id = o.user_id
WHERE u.created_at > '2024-01-01'::date
GROUP BY u.id, u.name;
 
-- Identify slow queries from pg_stat_statements
SELECT query, calls, total_time, mean_time, rows,
       100.0 * shared_blks_hit / nullif(shared_blks_hit + shared_blks_read, 0) AS hit_percent
FROM pg_stat_statements 
ORDER BY total_time DESC 
LIMIT 10;

-- Composite indexes for multi-column queries
CREATE INDEX idx_orders_user_date ON orders(user_id, order_date);
 
-- Partial indexes for filtered queries
CREATE INDEX idx_active_users ON users(created_at) WHERE status = 'active';
 
-- Expression indexes for computed values
CREATE INDEX idx_users_lower_email ON users(lower(email));
 
-- Covering indexes to avoid table lookups
CREATE INDEX idx_orders_covering ON orders(user_id, status) INCLUDE (total, created_at);

-- Check connection usage
SELECT count(*) as connections, state 
FROM pg_stat_activity 
GROUP BY state;
 
-- Monitor memory usage
SELECT name, setting, unit 
FROM pg_settings 
WHERE name IN ('shared_buffers', 'work_mem', 'maintenance_work_mem');

-- Create custom types
CREATE TYPE address_type AS (
    street TEXT,
    city TEXT,
    postal_code TEXT,
    country TEXT
);
 
CREATE TYPE order_status AS ENUM ('pending', 'processing', 'shipped', 'delivered', 'cancelled');
 
-- Use domains for data validation
CREATE DOMAIN email_address AS TEXT 
CHECK (VALUE ~* '^[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}$');
 
-- Table using custom types
CREATE TABLE customers (
    id SERIAL PRIMARY KEY,
    email email_address NOT NULL,
    address address_type,
    status order_status DEFAULT 'pending'
);

-- PostgreSQL range types
CREATE TABLE reservations (
    id SERIAL PRIMARY KEY,
    room_id INTEGER,
    reservation_period tstzrange,
    price_range numrange
);
 
-- Range queries
SELECT * FROM reservations 
WHERE reservation_period && tstzrange('2024-07-20', '2024-07-25');
 
-- Exclude overlapping ranges
ALTER TABLE reservations 
ADD CONSTRAINT no_overlap 
EXCLUDE USING gist (room_id WITH =, reservation_period WITH &&);

-- PostgreSQL geometric types
CREATE TABLE locations (
    id SERIAL PRIMARY KEY,
    name TEXT,
    coordinates POINT,
    coverage CIRCLE,
    service_area POLYGON
);
 
-- Geometric queries
SELECT name FROM locations 
WHERE coordinates <-> point(40.7128, -74.0060) < 10; -- Within 10 units
 
-- GiST index for geometric data
CREATE INDEX idx_locations_coords ON locations USING gist(coordinates);

-- Enable commonly used extensions
CREATE EXTENSION IF NOT EXISTS "uuid-ossp";    -- UUID generation
CREATE EXTENSION IF NOT EXISTS "pgcrypto";     -- Cryptographic functions
CREATE EXTENSION IF NOT EXISTS "unaccent";     -- Remove accents from text
CREATE EXTENSION IF NOT EXISTS "pg_trgm";      -- Trigram matching
CREATE EXTENSION IF NOT EXISTS "btree_gin";    -- GIN indexes for btree types
 
-- Using extensions
SELECT uuid_generate_v4();                     -- Generate UUIDs
SELECT crypt('password', gen_salt('bf'));      -- Hash passwords
SELECT similarity('postgresql', 'postgersql'); -- Fuzzy matching

-- Database size and growth
SELECT pg_size_pretty(pg_database_size(current_database())) as db_size;
 
-- Table and index sizes
SELECT schemaname, tablename,
       pg_size_pretty(pg_total_relation_size(schemaname||'.'||tablename)) as size
FROM pg_tables 
ORDER BY pg_total_relation_size(schemaname||'.'||tablename) DESC;
 
-- Index usage statistics
SELECT schemaname, tablename, indexname, idx_scan, idx_tup_read, idx_tup_fetch
FROM pg_stat_user_indexes 
WHERE idx_scan = 0;  -- Unused indexes

-- Identify slow queries
SELECT query, calls, total_time, mean_time, rows
FROM pg_stat_statements 
ORDER BY total_time DESC 
LIMIT 10;
 
-- Check index usage
SELECT schemaname, tablename, indexname, idx_scan, idx_tup_read, idx_tup_fetch
FROM pg_stat_user_indexes 
WHERE idx_scan = 0;

-- ❌ BAD: OFFSET for large datasets
SELECT * FROM products ORDER BY id OFFSET 10000 LIMIT 20;
 
-- ✅ GOOD: Cursor-based pagination
SELECT * FROM products 
WHERE id > $last_id 
ORDER BY id 
LIMIT 20;

-- ❌ BAD: Inefficient grouping
SELECT user_id, COUNT(*) 
FROM orders 
WHERE order_date >= '2024-01-01' 
GROUP BY user_id;
 
-- ✅ GOOD: Optimized with partial index
CREATE INDEX idx_orders_recent ON orders(user_id) 
WHERE order_date >= '2024-01-01';
 
SELECT user_id, COUNT(*) 
FROM orders 
WHERE order_date >= '2024-01-01' 
GROUP BY user_id;

-- ❌ BAD: Inefficient JSON querying
SELECT * FROM users WHERE data::text LIKE '%admin%';
 
-- ✅ GOOD: JSONB operators and GIN index
CREATE INDEX idx_users_data_gin ON users USING gin(data);
 
SELECT * FROM users WHERE data @> '{"role": "admin"}';

-- Recursive queries for hierarchical data
WITH RECURSIVE category_tree AS (
    SELECT id, name, parent_id, 1 as level
    FROM categories 
    WHERE parent_id IS NULL
    
    UNION ALL
    
    SELECT c.id, c.name, c.parent_id, ct.level + 1
    FROM categories c
    JOIN category_tree ct ON c.parent_id = ct.id
)
SELECT * FROM category_tree ORDER BY level, name;