async def METHOD_NAME(index) -> list:
    memory_key = f"{index}-mapping-cache"
    if memory_key not in memory_cache:
        mapping = await storage_manager(index).get_mapping()
        fields = mapping.get_field_names()
        memory_cache[memory_key] = CacheItem(data=fields, ttl=5)  # result is cached for 5 seconds
    db_mappings = memory_cache[memory_key].data
    set_of_db_mappings = set(db_mappings)
    set_of_db_mappings.update(FieldMapper().get_field_mapping(index))
    return sorted(list(set_of_db_mappings))