i tried tingodb but tingodb doesn't store the indexes on disk, so you need to do some initialization work which was too slow on my tests.
I used also leveldb with json engine, and end up with loads of work to make it work on OSX and Windows, so end up giving up on it.
So far the only database that is working fast and reliable with indexes for my data ( which has more than 100k entries ) is SQLite, which to be honest is saving my day.
The issue is that i would like to use some document based DB, that would make it easier to integrate with my code but i could not find anything that would perform and work as fast and smooth on OSX and Windows, hence why i was hoping to embed mongodb.
Anyway thanks for your input!