def METHOD_NAME(collection_id):
    """Retrieve statistics on the content of a collection."""
    keys = {_facet_key(collection_id, f): f for f in STATS_FACETS}
    empty = {"values": [], "total": 0}
    stats = {}
    for key, result in cache.get_many_complex(keys.keys(), empty):
        stats[keys[key]] = result
    return stats