Cache patterns

Pattern	How	Good for	Catch
Cache-aside (lazy)	App reads cache; on miss reads DB and fills cache	Default for most reads	First read slow; stale until TTL/invalidate
Write-through	Write cache + DB together	Read-after-write freshness	Slower writes; caches data never read
Write-back	Write cache; flush to DB later	Write-heavy counters	Data loss if cache dies
Read-through	Cache library loads from DB itself	Same as aside, cleaner code	Coupling to cache lib

Cache-aside

def get_user(id):
    u = redis.get(f'user:{id}')
    if u: return u                     # hit
    u = db.query('SELECT ... WHERE id=%s', id)
    redis.set(f'user:{id}', u, ex=300)  # TTL 5 min
    return u

def update_user(id, data):
    db.update(id, data)
    redis.delete(f'user:{id}')          # invalidate, don't update