Does MongoDB ignore calling Reduce function when Map emits only one result?

[Rmon]

I notice that when the Map function returns one entry, then Reduce doesn't get called.

1. Is this the default behaviour?
2. Can MongoDB be forced to always call the Reduce function?

[Emily S]

If the map function emits a single document for a given key, the reduce function will not be called.

This is by design.  You can see the above note and read further documentation here:

http://www.mongodb.org/display/DOCS/MapReduce