This looks potentially interesting.
How does it scale? Would 200.000 notes be a problem? Does it handle pdf, epub or enex?
and most importantly
Search, what does it have and how good is it? (Is it better than evernote)?
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I also haven't really stress tested it, this was really more of a personal wiki that I wanted to create specifically with the hierarchical linking/backlinking that I didn't see any other notetaking applications having just the way I wanted. But since the application is relatively simple, I think Postgres should be able to handle the load.
It uses fulltext search built into Postgres for all the searching capabilities though, so hopefully it is good!