Re: ALTER TABLE ... NOREWRITE option

On 2012-12-01 12:24:57 -0800, Josh Berkus wrote:
> 
> >> I'm not thrilled about inventing YA keyword for this.  If you have a
> >> problem with that sort of scenario, why aren't you testing your DDL
> >> on a test server before you do it on production?
> 
> *I* do test my DDL.  However, there are literally hundreds of thousands
> of Rails, Django and Hibernate developers who "test" their DDL by
> running it using a 5-row dataset on their laptops before pushing it to
> production.  As far as these folks are concerned, "rewrite if there's a
> default" is a completely unintuitive booby-trap.
> 
> I agree that adding "NOREWRITE" is a bad solution, though.  Personally,
> I'd rather have a system function which tests whether a series of DDL
> statements involves a rewrite anywhere.  e.g.:
> 
> SELECT pg_test_for_rewrite('ALTER TABLE josh ADD COLUMN haircolor')
> 
> Hmmmm.  Actually, that wouldn't work with migrations tools, especially
> Rails.  Better, what about a GUC?
> 
> SET message_on_rewrite=WARNING;

If you have a framework and you want to test for this you can just
compare relfilenodes before/after.

Greetings,

Andres Freund

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