Comment by eknkc
2 years ago
As far as I can remember MongoDB did not have any dedicated block caching mechanism in its earlier releases.
They basically mmap’ed the database file and argued that OS cache should do its job. Which makes sense but I guess it did not perform as well as any fune tuned caching mechanism.
Early MongoDB design choices are probably not great to call out for anything other than ignorance. mmap is a very naive view on how to easily work with data but it falls over pretty hard for any situation where ensuring your data doesn't get corrupted is important. MongoDB has come a long way, but its early technical decisions were not based on technical insight.