Re: Proposal: In-Place upgrade concept

Martijn van Oosterhout wrote:
> On Tue, Jul 03, 2007 at 12:05:07PM +0100, Heikki Linnakangas wrote:
>>> This is actually a bit of a problem. We would need to know when we
>>> read in a page what the tupledescriptor for that relation looks like
>>> to know which fields are varlena. I'm not sure how easy it would be
>>> to arrange for the tuple descriptor to be passed down that far.
>> Speaking of on-the-fly upgrading, ReadBuffer is already passed the 
>> Relation, which contains the TupleDesc, so I don't think that's a 
>> problem. Not sure how easy that would be to do in an external program 
>> like pg_migrator.
> 
> My reading of this thread so far is that we're intending to upgrade
> pages on the fly? Which means that at any point in time, some pages
> will be converted and some not, so the tuple descriptor isn't going to
> help, surely you need some identifier on the page telling you if it's
> upgraded or not?

Yes, we already have such an identifier. The page layout version number 
is stored on every page.

--   Heikki Linnakangas  EnterpriseDB   http://www.enterprisedb.com