Data model and hierarchical namespace

The name space provided by ZooKeeper is much like that of a standard file system. The main differences between ZooKeeper and standard file systems are that

• every znode can have data associated with it (every file can also be a directory and vice-versa) and

• znodes are limited to the amount of data that they can have.

来源 ZooKeeper Documentation: Overview

ZooKeeper was designed to store coordination data: status information, configuration, location information, etc.

ZNode

Unlike files in file systems, znodes are not designed for general data storage. Instead, znodes map to abstractions of the client application, typically corresponding to meta-data used for coordination purposes.

There are two types of znodes that a client can create:

• Regular: Clients manipulate regular znodes by creating and deleting them explicitly;

• Ephemeral: Clients create such znodes, and they either delete them explicitly, or let the system remove them automatically when the session that creates them terminates (deliberately or due to a failure).