A Hadoop MapReduce is a software framework for easily writing Application for processing a large amount of data in parallel or on a large cluster of a commodity. As it deals with processing of data it is likely to be asked in Hadoop Interview. So in this section, we covered 60 MapReduce interview questions and answers framed by our company expert. These questions are as per the latest trend followed in an interview.
A Proper care has been taken while answering these questions. So we can provide you the best question and their answer. Hope these MapReduce interview questions will help you to crack Hadoop interview. All the best!!!!!!!
List of Top Hadoop MapReduce Interview Questions and Answers
1) What is Hadoop MapReduce?
2) What is the need of MapReduce?
3) What is Mapper in Hadoop MapReduce?
4) In MapReduce, ideally how many mappers should be configured on a slave?
5) How to set the number of mappers to be created in MapReduce?
6) Where is the output of Mapper written in Hadoop?
7) How to change a number of mappers running on a slave in MapReduce?
8) How to compress mapper output in Hadoop?
9) How to configure Hadoop to reuse JVM for mappers?
10) Why Mapper runs in heavy weight process and not in a thread in MapReduce?
11) What is Reducer in MapReduce?
12) How many numbers of reducers run in Map-Reduce Job?
13) Can we set the number of reducers to zero in MapReduce?
14) What happen if the number of the reducer is 0 in MapReduce?
15) What is the key- value pair in Hadoop MapReduce?
16) What is InputFormat in Hadoop MapReduce?
17) What are the various InputFormats in Hadoop?
18) Explain InputSplit in Hadoop MapReduce?
19) How much space will the split occupy in Mapreduce?
20) What is a RecordReader in Hadoop MapReduce?
21) What is the difference between HDFS block and input split?
22) How to write MapReduce Programs?
23) What is KeyValueTextInputFormat in Hadoop MapReduce?
24) Where sorting is done in Hadoop MapReduce Job?
25) What is Combiner in MapReduce?
26) In MapReduce Data Flow, when Combiner is called?
27) How to configure the number of the Combiner in MapReduce?
28) A number of combiners can be changed or not in MapReduce?
29) How many times combiner is called on a mapper node in Hadoop?
30) Differentiate Reducer and Combiner in Hadoop MapReduce?
31) Where sorting is done on mapper node or reducer node in MapReduce?
32) How to sort intermediate output based on values in MapReduce?
33) Which Sorting algorithm is used in Hadoop MapReduce?
34) What is the sequence of execution of map, reduce, recordreader, split, combiner, partitioner?
35) Whether the output of mapper or output of partitioner written on local disk?
36) Does Partitioner run in its own JVM or shares with another process?
37) What is the sequence of execution of Mapper, Combiner, and Partitioner in MapReduce?
38) What is a Distributed Cache in Hadoop?
39) What is the problem with the small file in Hadoop?
40) Why can aggregation not be done in Mapper in MapReduce?
41) Is reduce-only job possible in Hadoop MapReduce?
42) What is Output Format in MapReduce?
43) What is LazyOutputFormat in MapReduce?
44) How to specify more than one directory as input in the Hadoop MapReduce Program?
45) Why is output file name in Hadoop MapReduce part-r-00000?
46) How to change the name of the output file from part-r-00000 in Hadoop MapReduce?
47) How to get the single file as the output from MapReduce Job?
48) How to overwrite an existing output file/dir during execution of Hadoop MapReduce jobs?
49) How to optimize Hadoop MapReduce Job?
50) What is a speculative execution in Apache Hadoop MapReduce?
51) What is Data Locality in Hadoop?
52) What is the difference between Job and Task in MapReduce?
53) Explain slot in Hadoop Map-Reduce v1?
54) What are the the issues associated with the map and reduce slots based mechanism in mapReduce?
55) How to submit extra files(jars, static files) for Hadoop MapReduce job during runtime?
56) What are the identity mapper and reducer in MapReduce?
57) Explain the process of spilling in Hadoop MapReduce?
58) What is Counter in MapReduce?
59) How to cre a te custom key and custom value in MapReduce Job?
60) In which kind of scenarios MapReduce jobs will be more useful than PIG in Hadoop?
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