Switch to the target database to receive event notification messages. 切換到目標資料庫以接收事件通知消息。
Notification involves obtaining a lock to the critical section, iterating through the map, and notifying the subscribers. 事件通知首先會獲取一個臨界區鎖,然後遍歷關注者映射,對所有的關注者發送事件通知消息。