Comment 17 for bug 1890822

I see our commits crossed. Upon reviewing yours, I figured out that I was assuming that the transactions would behave as if they were at the repeatable read transaction isolation, which isn't the case: it's read committed by default in PostgreSQL. Consequently, I've tested and merged your final branch and added a follow-up to extend the documentation change and add a comment about the isolation level.

Thanks, Jane and Elizabeth!