Use MongoDB aggregation framework for computing statistics
Some of the statistics not computable by MongoDB 3.0's aggregation framework (e.g. standard deviation) can now be computed in MongoDB 3.2. We should look into how far it is possible to replace the current MapReduce approach with this instead, as MapReduce tend to be quite slow.
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information