Cache-aside

The application is responsible for reading and writing from storage. The cache does not interact with storage directly. The application does the following:

• Look for entry in cache, resulting in a cache miss

• Load entry from the database

• Add entry to cache

• Return entry

  def get_user(self, user_id): user = cache.get("user.{0}", user_id) if user is None: user = db.query("SELECT * FROM users WHERE user_id = {0}", user_id) if user is not None: key = "user.{0}".format(user_id) cache.set(key, json.dumps(user)) return user

Memcached is generally used in this manner. Subsequent reads of data added to cache are fast. Cache-aside is also referred to as lazy loading. Only the requested data is cached, which avoids filling up the cache with data that isn't requested.