Re: [WIP] In-place upgrade

> That's sane *if* you can guarantee that only negligible overhead is
> added for accessing data that is in the up-to-date format.  I don't
> think that will be the case if we start putting version checks into
> every tuple access macro.

Yes, the point is that you'll read the page as V3 or V4, whichever it
is, but if it's V3, you'll convert the tuples to V4 format before you
try to doing anything with them (for example by modifying
ExecStoreTuple to copy any V3 tuple into a palloc'd buffer, which fits
nicely into what that function already does).

...Robert