CAML query IN Clause limiation

Thanks for your reply, I have a follow up question regarding the case in general. As I mentioned I am following this approach in order to enhance the performance by avoiding the join between two tables and replace it by two separate CAML query calls and, after what I've learned from your replies, I will also have to write my own function to prepare the second CAML query by dividing the IN list into chunks of 500s.

Is this still a recommended approach (also hoping that the CAML grammar can overcome this limitation), or is it recommended to keep the join in one CAML query and try to figure other ways to enhance its performance?

Generally speaking, if the parent table is 250K+ records and the child is 1-M with the parent, is two CAML calls using IN faster (or more recommended) than CAML query with join?

Thanks,