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How Does MapReduce Work? map(k1, Getting Started on Hadoop

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How Does MapReduce Work?

map(k1, v1) → list(k2, v2)
reduce(k2, list(v2)) → list(v3)

Several phases, which partition a problem into many tasks:
• load data into DFS…
• map phase: input split → (key, value) pairs, with optional combiner
• shuffle phase: sort on keys to group pairs… load-test your network!
• reduce phase: each task receives the values for one key
• pull data from DFS…
NB: “map” phase is required, the rest are optional.
Think of set operations on tuples (and check out
Meanwhile, given all those (key, value) pairs listed above, it’s no
wonder that key/value stores have become such a popular topic of

Publicado en: Tecnología