Question

Point out the correct statement.

(a) The read phase takes a exclusive lock

(b) The map-reduce operation is composed of many tasks

(c) Prior to version 3, JavaScript code executed in a single thread

(d) All of the mentioned

This question was addressed to me during an interview for a job.

My question comes from Map-Reduce and Sharded Collections in chapter Aggregation Concepts and Aggregation Mechanics of MongoDB

Answer 1

Correct answer is (b) The map-reduce operation is composed of many tasks

Easiest explanation: It includes reads from the input collection, executions of the map function, executions of the reduce function, writes to a temporary collection during processing, and writes to the output collection.