jabref: Working with PostgreSQL database is unusably slow

@tobiasdiez I started writing the code to batch remove entries. I ended up changing EntryRemovedEvent to EntriesRemovedEvent and changing the code wherever it was subscribed to that event. It doesn’t compile because I haven’t finished. This is actually more of a refactoring of the entry events overall than specifically something that relates to database syncs. Also, I still have to look into if the tests need to be changed. I pushed it to a branch on my fork, linked below. Would you be interested in me making a PR for this?

https://github.com/NorwayMaple/jabref/commit/80e83772e77b2efc93f1b2715ae9106d463fd505

I think I figured out what the problem with trying to connect JabRef to Heroku Postgres is. It works out that Heroku does not negotiate with CA-verifiable certificates, but the Postgres JDBC wants to connect with sslmode set to verify-full. I am going to try another database.

Connecting to a remote PostGreSQL DB with ≈3,900 entries took 30 seconds for JabRef to show the entries in the window.

Exporting the same database as a *.bib file and opening this file from the same server (via mounted network share) using the same network connection took exactly the same time: 30 seconds.

So in response to my original problem, this is definitely a huge improvement! Thank you so much! It is well usable now! I apologize for my late response, as I have been totally overloaded at work.

For me, tests on the latest Windows built with a remote PostgreSQL server show the problem described in the issue is solved, but there are still many actions that remain slow:

• Opening a DB: now fast (a few seconds for a few hundreds of entries)
• Editing a field: still slow as I type the first character (~5 s), a bit faster for the second character, then it gets faster and good as I continue typing.
• Pasting, in the BibTeX tab, an entry containing several fields: still very slow (1-2 min).
• Switching tabs: takes a few seconds.