"""
Instrument dogpile.cache__ to report all cached lookups.

This will add spans around the calls to your cache backend (e.g. redis, memory,
etc). The spans will also include the following tags:

- key/keys: The key(s) dogpile passed to your backend. Note that this will be
  the output of the region's ``function_key_generator``, but before any key
  mangling is applied (i.e. the region's ``key_mangler``).
- region: Name of the region.
- backend: Name of the backend class.
- hit: If the key was found in the cache.
- expired: If the key is expired. This is only relevant if the key was found.

While cache tracing will generally already have keys in tags, some caching
setups will not have useful tag values - such as when you're using consistent
hashing with memcached - the key(s) will appear as a mangled hash.
::

    # Patch before importing dogpile.cache
    from ddtrace import patch
    patch(dogpile_cache=True)

    from dogpile.cache import make_region

    region = make_region().configure(
        "dogpile.cache.pylibmc",
        expiration_time=3600,
        arguments={"url": ["127.0.0.1"]},
    )

    @region.cache_on_arguments()
    def hello(name):
        # Some complicated, slow calculation
        return "Hello, {}".format(name)

.. __: https://dogpilecache.sqlalchemy.org/
"""