>Yes. 8 bytes for BigInt.
>
>BTW, don't forget that you can use negative values for Integer key. So, if you only used positive values, there is a possibility to go negative and keep Int.

Yes, but I wouldn't want to start supporting that.

>But if you anticipate you do need to use BigInt, so be it. It would be a pain to change the existing type, though.

That would require a new field, dump everything into the new field, remove the old one, readjust the primary key index, etc.