Re: --single-transaction hack to pg_upgrade does not work

On 2012-12-01 13:43:44 -0500, Bruce Momjian wrote:
> On Sat, Dec  1, 2012 at 07:32:48PM +0100, Andres Freund wrote:
> > On 2012-12-01 12:14:37 -0500, Tom Lane wrote:
> > > Andres Freund <andres@2ndquadrant.com> writes:
> > > > On 2012-12-01 12:00:46 -0500, Tom Lane wrote:
> > > >> ISTM this sort of thing ought to be safe enough, though you probably
> > > >> need to insist both that the pg_type row's xmin be current XID and
> > > >> that it not be HEAP_UPDATED.
> > >
> > > > I was concerned about updated rows but forgot about HEAP_UPDATED. So I
> > > > thought that it would be possible to alter the type in some generic
> > > > fashion (e.g. change owner) and then add new values.
> > >
> > > Yeah, I was just thinking about that: we'd have to fail if pg_dump
> > > emitted CREATE TYPE, ALTER TYPE OWNER, and then tried to add more
> > > values.  Fortunately it doesn't do that; the ADD VALUE business is
> > > just a multi-statement expansion of CREATE TYPE AS ENUM, and any
> > > other ALTERs will come afterwards.
> >
> > Well, there's a binary_upgrade.set_next_pg_enum_oid() inbetween, but thats
> > luckily just fine.
>
> Do we need a comment in pg_dump.c to make sure that doesn't change?

We could, but I don't really see it likely that somethig problematic
will be added there the regression tests should catch any problem
there (right?).

> > > > Let me provide something a littlebit more mature.
> > >
> > > It could do with some comments ;-)
> >
> > Hehe, yes. Hopefully this version has enough of that.
>
> I believe this text in alter_type.sgml need updating:
>
>    <command>ALTER TYPE ... ADD VALUE</> (the form that adds a new value to an
>    enum type) cannot be executed inside a transaction block.

I purposefully didn't change that because the new support is rather
minimalistic. E.g. BEGIN; CREATE TYPE foo AS ENUM(); ALTER TYPE foo
RENAME TO bar; ALTER TYPE bar ADD VALUE 'blub'; COMMIT; is not going to
work. So it seems best not to make it something official but keep it as
an extension for pg_upgrade support.

(btw, the commit message inside the git am'able patch contained
that explanation...)

Greetings,

Andres Freund

--Andres Freund                       http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
Services