mapReduce

The now freely available framework that gave Google infinite ability to acquire and manipulate data. It describes a way to distribute the power of a master node over an infinite number of worker nodes.

The canonical example application of MapReduce is a process to count the appearances of each different word in a set of documents:

void map(String name, String document):

// name: document name

// document: document contents

for each word w in document:

EmitIntermediate(w, "1");

void reduce(String word, Iterator partialCounts):

// word: a word

// partialCounts: a list of aggregated partial counts

int sum = 0;

for each pc in partialCounts:

sum += ParseInt(pc);

Emit(word, AsString(sum));

-From Wikipedia