Re: extension facility (was: revised hstore patch)

On Jul 23, 2009, at 2:44 AM, "David E. Wheeler" <david@kineticode.com>  
wrote:

> On Jul 22, 2009, at 1:11 PM, Robert Haas wrote:
>
>> If you keep an old and a new version of the datatype, you can't
>> upgrade a tuple at a time, but you can at least upgrade one column at
>> a time, which is still better than a kick in the head.
>
> And as long as you're willing to deprecate how far back you'll go in  
> doing such updates, thus keeping the maintenance of your code  
> reasonable over time.

Of course.

>
>> If you make the extension-upgrade facility rewrite everything, you
>> have to do your entire cluster in one shot.  That will work for some
>> people, but not for all.  And unless you ship both versions of hstore
>> with either PG 8.4 or PG 8.5, you're going to need the conversion to
>> be done inside pg_migrator, which introduces a whole new level of
>> complexity that I think we'd be better off without.
>
> Well, it depends. If there could be some sort of defined interface  
> for pg_migrator could call to migrate any data type (this issue  
> applies mainly to types, yes?), then an extension author just needs  
> to implement that interface. No?

Yes... but "if" and "just" can paper over a good deal of complexity,  
and it's not clear to me that there's any compensating advantage.

...Robert