Hadoop编程世界中的关键字上下文是什么？

问题描述

在新的API条款中，Hadoop MapReduce世界中的关键字 Context 到底是什么？

将输出对写出Maps和Reduce，但是我不确定它是否可以在其他地方使用，以及每当使用上下文时会发生什么。它是不同名称的迭代器吗？

Class Mapper.Context，Class Reducer.Context和Job.Context之间的关系是什么？

请从外行的条款开始解释，然后详细介绍。

感谢您的时间和帮助。

解决方案

上下文对象：允许Mapper / Reducer与Hadoop系统的其余部分进行交互。它包含作业的配置数据以及允许它发出输出的接口。

应用程序可以使用上下文：

• 报告进度


• 设置应用程序级状态消息
  
• 更新计数器


• 表示它们还活着


• 可以通过map / reduce阶段获取作业配置中存储的值。
  

What exactly is this keyword Context in Hadoop MapReduce world in new API terms?

Its extensively used to write output pairs out of Maps and Reduce, however I am not sure if it can be used somewhere else and what's exactly happening whenever I use context. Is it a Iterator with different name?

What is relation between Class Mapper.Context, Class Reducer.Context and Job.Context?

Can someone please explain this starting with Layman's terms and then going in detail. Not able understand much from Hadoop API documentations.

Thanks for your time and help.

解决方案

Context object: allows the Mapper/Reducer to interact with the rest of the Hadoop system. It includes configuration data for the job as well as interfaces which allow it to emit output.

Applications can use the Context:

• to report progress
• to set application-level status messages
• update Counters
• indicate they are alive
• to get the values that are stored in job configuration across map/reduce phase.

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