What is the difference between namenode and datanode in hadoop?

495

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Ideally what should be the replication factor in hadoop?

425

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What is rack awareness in hadoop?

487

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While starting hadoop services, datanode service is not running?

439

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what happens when namenode goes down during file read operation in hadoop?

587

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Why slaves limited to 4000 in hadoop version 1?

487

---

What is heartbeat in hadoop?

424

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Explain small file problem in hadoop

421

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How to create the directory when name node is in safe mode?

543

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Why can we not create directory /user/dataflair/inpdata001 when name node is in safe mode?

449

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Ideally what should be the block size in hadoop?

459

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What happen when namenode enters in safemode in hadoop?

423

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What is shuffleing in mapreduce?

646

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Does mapreduce programming model provide a way for reducers to communicate with each other? In a mapreduce job can a reducer communicate with another reducer?

675

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How would you tackle calculating the number of unique visitors for each hour by mining a huge apache log? You can use post processing on the output of the mapreduce job.

822

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