Does everyone hate MongoDB?
MongoDB uses unsafe writes by default in the sense that from the driver, you do not know if the write has succeeded without a further call to getLastError. This is because one of the often cited use cases for MongoDB is fast writes, which is achieved by fire and forget queries.
.. Getting your working set in memory is one of the most difficult things to calculate and plan for with MongoDB.
.. A general guideline is to provide as much RAM as you can to fit all your data plus indexes or if that’s not possible, at least your indexes