Book Image

Apache ZooKeeper Essentials

By : Haloi
Book Image

Apache ZooKeeper Essentials

By: Haloi

Overview of this book

Whether you are a novice to ZooKeeper or already have some experience, you will be able to master the concepts of ZooKeeper and its usage with ease. This book assumes you to have some prior knowledge of distributed systems and high-level programming knowledge of C, Java, or Python, but no experience with Apache ZooKeeper is required.
Table of Contents (9 chapters)
4
4. Performing Common Distributed System Tasks
8
Index

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...