DATABASE FUNDAMENTALS
BASICS OF BIG DATA
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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A client writing a file to HDFS.
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A client requesting the filename of a given block of data.
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A client reading a block of data from the cluster.
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A client reading a file from the cluster.
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Detailed explanation-1: -For which of the following operations is NO communication with the NameNode required? A client writing a file to HDFS.
Detailed explanation-2: -To read a file from HDFS, a client needs to interact with namenode (master) as namenode is the centerpiece of Hadoop cluster (it stores all the metadata i.e. data about the data).
Detailed explanation-3: -NameNode only stores the metadata of HDFS – the directory tree of all files in the file system, and tracks the files across the cluster. NameNode does not store the actual data or the dataset. The data itself is actually stored in the DataNodes.
Detailed explanation-4: -Answer: The client reading the data from the HDFS filesystem in Hadoop gets the block location from the Namenode and then gets the data from the Datanode.
Detailed explanation-5: -The DataNodes talk to the NameNode using the DataNode Protocol. A Remote Procedure Call (RPC) abstraction wraps both the Client Protocol and the DataNode Protocol. By design, the NameNode never initiates any RPCs. Instead, it only responds to RPC requests issued by DataNodes or clients.