[rosser]

I don't remember specifically, but I believe it was in the thousands to low tens of thousands of rows. It's also not consistent. I've seen larger IN() clauses that never have a problem, and smaller ones that consistently do. It's been on my very low priority to-do list to put together some demo cases for the mailing lists, because overnight to < 4s just from that little refactor isn't the greatest...

[tmoertel]

Are we talking about IN clauses that contain a correlated subquery or something the optimizer would have a hard time determining was independent of outer context?

[jeltz]

PostgreSQL is able to convert correlated subqueries with IN () clauses into joins in most cases. My guess is that it could have been two queries refactored into one.