Re: [WIP] In-place upgrade

"Robert Haas" <robertmhaas@gmail.com> writes:
> Well, I just proposed an approach that doesn't work this way, so I
> guess I'll have to put myself in the disagree category, or anyway yet
> to be convinced.  As long as you can move individual tuples onto new
> pages, you can eventually empty V3 pages and reinitialize them as new,
> empty V4 pages.  You can force that process along via, say, VACUUM,
> but in the meantime you can still continue to read the old pages
> without being forced to change them to the new format.  That's not the
> only possible approach, but it's not obvious to me that it's insane.
> If you think it's a non-starter, it would be good to know why.

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.
        regards, tom lane