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The NameNode uses RAM for the following purpose:

The NameNode uses RAM for the following purpose:

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A.
To store the contents of files in HDFS.

B.
To store filenames, list of blocks and other meta information.

C.
To store the edits log that keeps track of changes in HDFS.

D.
To manage distributed read and write locks on files in HDFS.

Explanation:
The NameNode is the centerpiece of an HDFS file system. It keeps the directory
tree of all files in the file system, and tracks where across the cluster the file data is kept. It does
not store the data of these files itself. There is only One NameNode process run on any hadoop
cluster. NameNode runs on its own JVM process. In a typical production cluster its run on a
separate machine. The NameNode is a Single Point of Failure for the HDFS Cluster. When the
NameNode goes down, the file system goes offline. Client applications talk to the NameNode
whenever they wish to locate a file, or when they want to add/copy/move/delete a file. The
NameNode responds the successful requests by returning a list of relevant DataNode servers
where the data lives
Reference:24 Interview Questions & Answers for Hadoop MapReduce developers,What is a
NameNode? How many instances of NameNode run on a Hadoop Cluster?

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