MongoDB Questions and Answers – Map-Reduce

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This set of MongoDB Multiple Choice Questions & Answers (MCQs) focuses on “Map-Reduce”.

1. Which of the following database command is used for mapreduce function?
a) mapReduce
b) mapperRed
c) redmap
d) none of the mentioned
View Answer

Answer: a
Explanation: For map-reduce operations, MongoDB provides the mapReduce database command.

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2. MongoDB applies the _____ phase to each input document in mapreduce.
a) map
b) reduce
c) mapper
d) all of the mentioned
View Answer

Answer: a
Explanation: The map function emits key-value pairs.

3. MongoDB applies the _________ phase, which collects and condenses the aggregated data.
a) map
b) reduce
c) mapper
d) all of the mentioned
View Answer

Answer: b
Explanation: MongoDB then stores the results in a collection.

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4. The output of the reduce function may pass through a ______ function to further condense or process the results of the aggregation.
a) finalize
b) filter
c) procedure
d) none of the mentioned
View Answer

Answer: a
Explanation: The input and the output collections may be sharded.

5. _________ can return the results of a map-reduce operation as a document, or may write the results to collections.
a) mapReduce
b) mapperRed
c) RedMap
d) none of the mentioned
View Answer

Answer: a
Explanation: Map-reduce operations take the documents of a single collection as the input and can perform any arbitrary sorting and limiting before beginning the map stage.

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6. Map-reduce uses custom __________ functions to perform the map and reduce operations.
a) Java
b) Javascript
c) JSON
d) None of the mentioned
View Answer

Answer: b
Explanation: JavaScript provide great flexibility compared to the aggregation pipeline.

7. For most aggregation operations, the ______ Pipeline provides better performance and more coherent interface.
a) Aggregate
b) Replication
c) Sharding
d) None of the mentioned
View Answer

Answer: a
Explanation: Map-reduce operations provide some flexibility that is not presently available in the aggregation pipeline.

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8. What would be the maximum document size for results of mapreduce operation?
a) 15 MB
b) 16 MB
c) 17 MB
d) All of the mentioned
View Answer

Answer: b
Explanation: When returning the results of a map reduce operation inline, the result documents must be within the BSON Document Size limit, which is currently 16 megabytes.

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Here’s the list of Best Books in MongoDB.

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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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