How a client reads a file from HDFS

Question

I am new to Hadoop and what I've done is I copied a file from my local system to HDFS. Now, I am reading this file from HDFS to process the data using MapReduce. Can someone tell me that how a client reads a file from HDFS.

Answer 1

Let me explain you it briefly. So, what happens is that the Client communication to HDFS happens using Hadoop HDFS API. Client applications talk to the NameNode whenever they wish to locate a file, or when they want to add/copy/move/delete a file on HDFS. The NameNode responds the successful requests by returning a list of relevant DataNode servers where the data lives. Client applications can talk directly to a DataNode, once the NameNode has provided the location of the data.

Hope this helps!