April 2015
Beginner to intermediate
754 pages
21h 39m
English
Content preview from Hadoop: The Definitive Guide, 4th EditionBecome an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.
Appendix D. The Old and New Java MapReduce APIs
The Java MapReduce API used throughout this book is called the “new API,” and it replaces the older,
functionally equivalent API. Although Hadoop ships with both the old and new MapReduce APIs,
they are not compatible with each other. Should you wish to use the old API, you can, since the
code for all the MapReduce examples in this book is available for the old API on the book’s
website (in the oldapi package).
There are several notable differences between the two APIs:
The new API is in the
org.apache.hadoop.mapreducepackage (and subpackages). The old API can still be found inorg.apache.hadoop.mapred.The new API favors abstract classes over interfaces, since these are easier to evolve. This means that you can add a method (with a default implementation) to an abstract class without breaking old implementations of the class.[168] For example, the
MapperandReducerinterfaces in the old API are abstract classes in the new API.The new API makes extensive use of context objects that allow the user code to communicate with the MapReduce system. The new
Context, for example, essentially unifies the role of theJobConf, theOutputCollector, and theReporterfrom the old API.In both APIs, key-value record pairs are pushed to the mapper and reducer, but in addition, the new API allows both mappers and reducers to control the execution flow by overriding the
run()method. For example, records can be processed in batches, or the execution can ...
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Read now
Unlock full access
More than 5,000 organizations count on O’Reilly
O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.