There is a tongue-in-cheek statement about MongoDB attributed to an unknown Twitter user: "If a MongoDB query runs for longer than 0ms, then something is wrong." This is typical of the kind of buzz that surrounded the product when it first burst onto the scene about a year ago.
The reality is that MongoDB is extraordinarily fast. But if you give it the wrong data structures, or you don't set up the database or collections with the right indexes, then MongoDB can slow down dramatically, like any data storage system.
MongoDB also contains some advanced features, such as grouping and map/reduce, that require some tuning to get them running with optimal efficiency.
The design of your data schemas can also have a big impact on ...