Apache ZooKeeper

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ZooKeeper - Watches
   

== Watches ==

Similar to triggers in databases, ZooKeeper provides watches. The objective of watches is to get notified when znode changes in some way. Watchers are triggered only once. If you want recurring notifications, you will have re-register the watcher.

The read operations such as exists, getChildren, getData may create watches. Watches are triggered by write operations: create, delete, setData. Access control operations do not participate in watches.

WATCH OF exists is TRIGGERED WHEN ZNODE IS created, deleted, or its data updated. WATCH OF getData is TRIGGERED WHEN ZNODE IS deleted or has its data updated. WATCH OF getChildren is TRIGGERED WHEN ZNODE IS deleted, or its any of the child is created or deleted