Answer / Yogendra Kumar

In Apache Hadoop, when a block of data is added to the system, it is broken down into smaller chunks (64 MB by default) and distributed across multiple DataNodes. The choice of which DataNode receives each chunk is based on the replica placement policy.

What is the default block size in hdfs?

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What is HDFS Federation?

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How would you use Map/Reduce to split a very large graph into smaller pieces and parallelize the computation of edges according to the fast/dynamic change of data?

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What is Apache Hadoop?

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How to resolve ioexception: cannot create directory, while formatting namenode in hadoop?

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What Mapper does?

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How can you connect an application

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Why we cannot do aggregation (addition) in a mapper? Why we require reducer for that?

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How is security achieved in Apache Hadoop?

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Data Engineer Given a list of followers in the format:123, 345234, 678345, 123…Where column one is the ID of the follower and column two is the ID of the followee. Find all mutual following pairs (the pair 123, 345 in the example above). How would you use Map/Reduce to solve the problem when the list does not fit in memory?

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What is the jobtracker and what it performs in a hadoop cluster?

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Explain how input and output data format of the hadoop framework?

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