Collect and remove all :class:`.RequestInfo` objects older than
    `time_limit` (in seconds).

    Args:
        time_limit (float, default YEAR / 2): Collect objects older than
            this limit.

def garbage_collection(time_limit=YEAR/12.0):
    """
    Collect and remove all :class:`.RequestInfo` objects older than
    `time_limit` (in seconds).

    Args:
        time_limit (float, default YEAR / 2): Collect objects older than
            this limit.
    """
    expired_request_infos = (
        ri for ri in DATABASE.values()
        if ri.creation_ts + time_limit <= time.time()
    )

    for ri in expired_request_infos:
        del DATABASE[ri.url]