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 requested data is cached, which avoids filling up the cache with data that isn’t requested.

To learn more, have a look at the following resources:

• From cache to in-memory data grid