During map-reduce operation there are unnecessary global lock used and should be removed.
Mapreduce uses global lock when outputting to empty collection
Convert GlobalWrite to db lock in mr.cpp
Possible to prevent global lock during map reduce?
mapReduce nonAtomic output option
Map/reduce documentation is wrong about write lock
Global Lock in Reduce Phase of Map/Reduce
m/r: reduce post processing: reduce lock time with "nonAtomic" option
GG: Global lock shoots to 100% during reduce post processing
mapReduce: Output to a Collection with an Action
Pull Request #333