Für große Datenmengen empfehle ich Indizes:
• chat_messages: (place_key, room_id, created_at), (place_key, room_id, is_deleted, created_at), (place_key, room_id, user_id, created_at)
• district messages: (district_key, room_id, created_at), (district_key, room_id, is_deleted, created_at), (district_key, room_id, user_id, created_at)
• chat_rooms: (place_key), district_chat_rooms: (district_key)