At that point it was webscale ready. The problem was that MongoDB lied in their documentation what guarantees it provided. It took them a decade to improve, and

At that point it was webscale ready. The problem was that MongoDB lied in their documentation what guarantees it provided. It took them a decade to improve, and now that data is safer (still not completely) it no longer offers performance edge over its competition. Originally it was super fast, because it kept everything in RAM and didn't worry about writing data to disk, which caused many people to lose data.