Re: Pg_upgrade and toast tables bug discovered

On 2014-07-10 16:33:40 -0400, Bruce Momjian wrote:
> On Thu, Jul 10, 2014 at 10:46:30AM -0400, Robert Haas wrote:
> > > Agreed. I am now thinking we could harness the code that already exists
> > > to optionally add a TOAST table as part of ALTER TABLE ADD COLUMN. We
> > > would just need an entry point to call it from pg_upgrade, either via an
> > > SQL command that checks (and hopefully doesn't do anything else), or a C
> > > function that does it, e.g. VACUUM would be trivial to run on every
> > > database, but I don't think it tests that; is _could_ in binary_upgrade
> > > mode. However, the idea of having a C function plug into the guts of
> > > the server and call internal functions makes me uncomforable.
> >
> > Well, pg_upgrade_support's charter is basically to provide access to
> > the guts of the server in ways we wouldn't normally allow; all that
> > next-OID stuff is basically exactly that. So I don't think this is
> > such a big deal. It needs to be properly commented, of course.
>
> If you look at how oid assignment is handled, it is done in a very
> surgical way, i.e. pg_upgrade_support sets a global variable, and the
> variable triggers different behavior in a CREATE command. This change
> would be far more invasive than that.

Meh. It's only somewhat surgical because there's pg_upgrade specific
code sprinkled in the backend at strategic places. That's the contrary
of a clear abstraction barrier. And arguably a function call from a SQL
C function has a much clearer abstraction barrier.

Greetings,

Andres Freund

--
Andres Freund http://www.2ndQuadrant.com/
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