versions of Couchdb Map-Reduce:
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Couchdb Map-Reduce
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Summary
Memorize core concepts of how couchdb implements map-reduce.
Basic
| Question (memorize) | Answer (memorize) |
|---|
| 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 |
Advanced
| Question (memorize) | Answer (memorize) |
|---|
| 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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