What is the Watch mechanism in ZooKeeper?

The Watch mechanism in ZooKeeper is an event listening mechanism used to notify clients about changes in the status of a specific node. When a client registers a Watch event for a node, if the node’s status changes (such as the data being updated, the node being created or deleted, etc.), ZooKeeper will notify the client, allowing the client to perform the corresponding operation upon receiving the notification.

The Watch mechanism allows clients to monitor node changes in real time, preventing the need for clients to constantly poll node status. It is an important feature of ZooKeeper for implementing distributed coordination, helping clients respond in real time to changes in node status within the cluster, maintaining data consistency and reliability.