Cloudera Hadoop Developer Certification Questions and Answer (Dumps and Practice Questions)

Question : If a Mapper runs slow relative to other than ?

1. No reducer can start until last Mapper finished
2. If mapper is running slow then another instance of Mapper will be started by Hadoop on another machine
3. Hadoop will kill the slow mapper if it keep running if the new one finished
4. The result of the first mapper finished will be used
5. All of the above

Correct Answer : 5

Explanation: It is possible for one Map Task to run more slowly than the others.

-- Perhaps due to faulty Hardware, or just a very slow machine.
-- The reduce method in the Reducer cannot start until every Mapper has finished.

Hadoop Uses Speculative Execution :
-- If a Mapper appears to be running significantly more slowly than the others, a new instance of Mapper will be
started on another machine, operating on same machine.

-- The result of the first Mapper to finish will be used.
-- Hadoop will kill off the Mapper which is still running.

Refer HadoopExam.com Recorded Training Module : 3 and 4

Question : What is the Combiner ?

1. Runs locally on a single Mappers output
2. Using Combiner can reduce the network traffic
3. Generally, Combiner and Reducer code is same
4. None of the 1,2 and 3
5. All 1,2 and 3 applicable to the Combiner

Correct Answer : 5

Often, Mappers produce large amounts of intermediate data
- The data must be passed to the Reducers
- This can result in a lot of network traffic.

You can specify the Combiner, which is consider mini-reducer
- Combiner runs locally on a single Mappers output.
- Output from the Combiner is sent to the Reducers.
- Input and Output data types for the Combiner and Reducer must be identical.

Combiner can be applied only when operation performed is commutative and associative.

Note : The Combiner may run once, or more than once, on the output from any given Mapper.

Do not put the in the Combiner which could influence your results if it runs more than once.

Refer HadoopExam.com Recorded Training Module : 3

Question : Using the Combiner will increase the network overhead ?

1. True
2. False

Correct Answer : 2

Explanation: Often, Mappers produce large amounts of intermediate data
- The data must be passed to the Reducers
- This can result in a lot of network traffic.

You can specify the Combiner, which is consider mini-reducer
- Combiner runs locally on a single Mappers output.
- Output from the Combiner is sent to the Reducers.
- Input and Output data types for the Combiner and Reducer must be identical.

Combiner can be applied only when operation performed is commutative and associative.

Refer HadoopExam.com Recorded Training Module : 3Often, Mappers produce large amounts of intermediate data
- The data must be passed to the Reducers
- This can result in a lot of network traffic.

You can specify the Combiner, which is consider mini-reducer
- Combiner runs locally on a single Mappers output.
- Output from the Combiner is sent to the Reducers.
- Input and Output data types for the Combiner and Reducer must be identical.

Combiner can be applied only when operation performed is commutative and associative.

Note : The Combiner may run once, or more than once, on the output from any given Mapper.

Do not put the in the Combiner which could influence your results if it runs more than once.

Refer HadoopExam.com Recorded Training Module : 3

Cloudera Hadoop Developer Certification Questions and Answer (Dumps and Practice Questions)

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