What is rack awareness in hadoop?

487

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While starting hadoop services, datanode service is not running?

437

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

585

---

Why slaves limited to 4000 in hadoop version 1?

487

---

What is heartbeat in hadoop?

424

---

Explain small file problem in hadoop

421

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

543

---

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

449

---

Ideally what should be the block size in hadoop?

459

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What happen when namenode enters in safemode in hadoop?

423

---

What is shuffleing in mapreduce?

646

---

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?

673

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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

---

Describe what happens to a mapreduce job from submission to output?

663

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If reducers do not start before all mappers finish then why does the progress on mapreduce job shows something like map(50%) reduce(10%)? Why reducers progress percentage is displayed when mapper is not finished yet?

710

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