Re: [WIP] In-place upgrade

> I see. But Vacuum and other internals function access heap pages directly
> without ExecStoreTuple.

Right. I don't think there's any getting around the fact that any
function which accesses heap pages directly is going to need
modification. The key is to make those modifications as non-invasive
as possible. For example, in the case of vacuum, as soon as it
detects that a V3 page has been read, it should call a special
function whose only purpose in life is to move the data out of that V3
page and onto one or more V4 pages, and return. What you shouldn't do
is try to make the regular vacuum code handle both V3 and V4 pages,
because that will lead to code that may be slow and will almost
certainly be complicated and difficult to maintain.

I'll read through the rest of this when I have a bit more time.

...Robert