Introduction and features of Hadoop core components zookeeper

Zookeeper is a reliable coordination system for large-scale distributed systems.

1) It provides functions including: Configuration maintenance, Name service, distributed synchronization, group service, etc.

2) Its goal is to encapsulate the complex error-prone key services, the easy-to-use interface and performance-efficient, stable system to provide users;

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Characteristics:

1, Final consistency: show the same attempt for the client

2, Reliability: If a message is accepted by a single server, it will be accepted by all servers.

3, real-time: Zookeeper does not guarantee that two clients have the data just updated at the same time, if you need the latest data, you should call the sync () interface before reading the data.

4, wait unrelated (Wait-free): Slow or invalid client does not intervene in fast client requests.

5, atomicity: The update operation either succeeds or fails with no intermediate state.

6, Sequential: For all servers, the same message is published in a consistent order.

Basic principle

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Server many, there are master and slave points, but there is a leader, the other is follower,

Each server, in memory, holds a piece of data that, when launched, will elect a leader, elected under the Poxos agreement

Leader is responsible for handling data update operations, using the ZAB protocol

A successful flag for the update operation, most servers in memory, successfully modified data (one with 5, 3 write succeeded)

This article is from the "I am the program my biggest" blog, please be sure to keep this source http://skinglzw.blog.51cto.com/10729606/1833186

Introduction and features of Hadoop core components zookeeper