MapReduce API has two main classes which do the Map-Reduce task for us: Mapper class and Reducer class.
Simple” often sense as “elegant” when it comes to those remarkable architectural drawings for that new Silicon Valley mansion we have planned for when the money starts rolling in after we implement Hadoop.
With the release of Hadoop 2, however, YARN was introduced, which open doors for whole new world of data processing opportunities.
Mapper class is responsible for providing implementations for mapping jobs in MapReduce.
HDFS is one of the two main components of the Hadoop framework; the other is the computational paradigm known as MapReduce.
In HDFS, the Data block size needs to be large enough to warrant the resources dedicated to an individual unit of data processing On the other hand.
Hadoop has gone through some big API change in its 0.20 release, which is the basic interface in the 1.0 version .
As we already know that in Hadoop, files are composed of individual records, which are ultimately processed one-by-one by mapper tasks.
Some amount of data volume that ends up in HDFS might land there through database load operations or other types of batch processes.
Whenever a user tries to stores a file in HDFS, the file is first break down into data blocks, and three replicas of these data blocks are stored in slave nodes (data nodes) throughout the Hadoop cluster
As we already know now that HDFS is a journaled file system, where new changes to files in HDFS are captured in an edit log that’s stored on the NameNode in a file named edits.
The massive data volumes that are very command in a typical Hadoop deployment make compression a necessity.