Re: pg_upgrade: downgradebility

Gavin Sherry wrote:
> On Wed, 20 Sep 2006, Andrew Sullivan wrote:
>
>> On Wed, Sep 20, 2006 at 12:54:14PM +0200, Zdenek Kotala wrote:
>>> My first question is how important is downgrade for You and Your customers?
>>>
>>>
>>> And second is how to verify that downgrade is possible?
>> Well, one way to do it is to set up a Slony replica using the older
>> version of the software. So, if you've upgraded to 8.1.x, you
>> replicate to an old 8.0.x back end as well. If 8.1 doesn't work for
>> you, you just MOVE everything back to the 8.0.x back end, and you're
>> golden.
>
> Well, I think that people who really want downgrade in such a tool are
> those for which slony replication is just not an option. That is, data in
> the range of hundreds of gigabytes. Using slony to upgrade is often not
> practical either

I agree with Gavin, Slony need a lot of extra resources. It is similarly
to use pg_dump for upgrade/downgrade.

> I wonder if pg_upgrade could be designed in such a way that upgrade is the
> same as downgrade from a development point of view. That is, the tool can
> change the system from one binary format to another.

The main problem is that newer format has more functionality that older.
There is not possible perform downgrade if some create store procedure
with SQL command which is not supported in the older version. Downgrade
must check it but is it possible to perform 100% check now (without
postgres code change)?

Zdenek