COMPUTER SCIENCE AND ENGINEERING
CLOUD COMPUTING
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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A map() function can emit up to a maximum number of key/value pairs (depending on the Hadoop environment).
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A map() function can emit anything between zero and an unlimited number of key/value pairs.
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A reduce() function can iterate over key/value pairs multiple times.
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A call to reduce() is guaranteed to receive key/value pairs from only one key.
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Detailed explanation-1: -Which of the following statements are true about key/value pairs in Hadoop? A map() function can emit up to a maximum number of key/value pairs (depending on the Hadoop environment). A map() function can emit anything between zero and an unlimited number of key/value pairs.
Detailed explanation-2: -Q 26-Which one of the following statements is true regarding <key, value> pairs of a MapReduce job? A-A key class must implement Writable.
Detailed explanation-3: -A key-value pair is a data type that includes two pieces of data that have a set of associated values and a group of key identifiers. Within a key-value pair, there are two related data elements. The first is a constant used to define the data set. The other is a value, which is a variable belonging to the data set.
Detailed explanation-4: -Answer: A MapReduce partitioner makes sure that all the value of a single key goes to the same reducer thus allows evenly distribution of the map output over the reducers.