Re: [WIP] In-place upgrade

Robert Haas wrote:
> The second point could probably be addressed with a GUC but the first
> one certainly can't.
> 
> 3. What about multi-release upgrades?  Say someone wants to upgrade
> from 8.3 to 8.6.  8.6 only knows how to read pages that are
> 8.5-and-a-half or better, 8.5 only knows how to read pages that are
> 8.4-and-a-half or better, and 8.4 only knows how to read pages that
> are 8.3-and-a-half or better.  So the user will have to upgrade to
> 8.3.MAX, then 8.4.MAX, then 8.5.MAX, and then 8.6.

Yes.

> It seems to me that if there is any way to put all of the logic to
> handle old page versions in the new code that would be much better,
> especially if it's an optional feature that can be compiled in or not.
>  Then when it's time to upgrade from 8.3 to 8.6 you could do:
> 
> ./configure --with-upgrade-83 --with-upgrade-84 --with-upgrade85
> 
> but if you don't need the code to handle old page versions you can:
> 
> ./configure --without-upgrade85
> 
> Admittedly, this requires making the new code capable of rearranging
> pages to create free space when necessary, and to be able to continue
> to execute queries while doing it, but ways of doing this have been
> proposed.  The only uncertainty is as to whether the performance and
> code complexity can be kept manageable, but I don't believe that
> question has been explored to the point where we should be ready to
> declare defeat.

And almost guarantee that the job will never be completed, or tested
fully.  Remember that in-place upgrades would be pretty painless so
doing multiple major upgrades should not be a difficult requiremnt, or
they can dump/reload their data to skip it.

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
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