Couchdb Map-Reduce

Summary

Memorize core concepts of how couchdb implements map-reduce.

Basic

Question	Answer
function that returns output from view	emit()
emit() parameters	key, value
views must be...	referentially transparent
reduce function must be...	referentially transparent, and able to reduce on it's own output (and get the same answer)
referentially transparent	given same input, always gives same output
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Advanced

Question	Answer
reduce() params (in general)	keys, values, rereduce
rereduce parameter	whether input comes from another call to reduce() (boolean)
reduce() params (when rereduce false)	[[key,id]...], [value...], false
reduce() params (when rereduce true)	null, [reduced...], true
groups of roughly __ are passed into reduce()	15
output flows from _____ to _____ to _____	map, reduce(...,false), reduce(...,true)
reduce() outputs...	whatever structure it wants
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