MapReduce
A programming model for processing Big Data by distributing computation across clusters. MapReduce enables scalable data analysis by parallelizing work.
Real World
Yahoo originally developed Hadoop's MapReduce implementation to index billions of web pages — the Map phase extracted keywords from each page, and Reduce aggregated page counts per keyword.
Exam Focus
Always describe both the Map and Reduce phases separately with a concrete key-value example; omitting either phase loses marks.
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