Unrelated to today's reading, I have a question about file uploads. Is the /uploads used by multer a directory or a collection? If it is a directory, how can we sync it between users? If it is a collection, how can we store the files themselves directly instead of paths in MongoDB? Thank you!

Why did we not need to use the conn object earlier in the course, but it is necessary with transactions in MongoDB? 

Could we go over the ACID operations? I didn't understand them

Could you expand on the isolation section of ACID? Especially the part where it mentions "...depending on the isolation level used.." what do different levels of isolation look like?

How do different levels of transaction isolation affect performance and consistency in a database