ALTER TABLE on system catalogs

On 20/08/2018 15:34, Tom Lane wrote:
> Andres Freund <andres@anarazel.de> writes:
>> On 2018-08-20 14:38:25 +0200, Peter Eisentraut wrote:
>>> Do you have an alternative in mind?
> 
>> One is to just not do anything. I'm not sure I'm on board with the goal
>> of changing things to make DDL on system tables more palatable.
> 
> FWIW, I agree with doing as little as possible here.  I'd be on board
> with Andres' suggestion of just swapping the two code stanzas so that
> the no-op case doesn't error out.  As soon as you go beyond that, you
> are in wildly unsafe and untested territory.

That doesn't solve the original problem, which is being able to set
reloptions on pg_attribute, because pg_attribute doesn't have a toast
table but would need one according to existing rules.

Attached is a patch that instead moves those special cases into
needs_toast_table(), which was one of the options suggested by Andres.
There were already similar checks there, so I guess this makes a bit of
sense.

-- 
Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services