Book Image

Apache ZooKeeper Essentials

By : Saurav Haloi
Book Image

Apache ZooKeeper Essentials

By: Saurav Haloi

Overview of this book

Table of Contents (14 chapters)
Apache ZooKeeper Essentials
About the Author
About the Reviewers
Performing Common Distributed System Tasks

Watches and ZooKeeper operations

The write operations in ZooKeeper are atomic and durable. There is the guarantee of a successful write operation if it has been written to persistent storage on a majority of ZooKeeper's servers. However, the eventual consistency model of ZooKeeper permits reads to log the latest state of the ZooKeeper service, and the sync operation allows a client to be up-to-date with the most recent state of the ZooKeeper service.

The read operations in znodes, such as exists, getChildren, and getData, allow watches to be set on them. On the other hand, the watches triggered by znode's write operations, such as create, delete, and setData ACL operations do not participate in watches.

The following are the types of watch events that might occur during a znode state change:

  • NodeChildrenChanged: A znode's child is created or deleted

  • NodeCreated: A znode is created in a ZooKeeper path

  • NodeDataChanged: The data associated with a znode is updated

  • NodeDeleted: A znode is deleted...