What is rack awareness in hadoop?

489

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While starting hadoop services, datanode service is not running?

440

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

599

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Why slaves limited to 4000 in hadoop version 1?

487

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What is heartbeat in hadoop?

426

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Explain small file problem in hadoop

428

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

550

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

454

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Ideally what should be the block size in hadoop?

461

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What happen when namenode enters in safemode in hadoop?

431

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What is shuffleing in mapreduce?

652

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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?

683

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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.

827

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

667

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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?

716

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