Re: ALTER TYPE 0: Introduction; test cases

On Tue, 2011-01-11 at 07:14 -0500, Noah Misch wrote:

> These changes do make it harder to guess how much work the ALTER TABLE
> will do. Indeed, about 1/4 of my own guesses prior to writing were
> wrong.  Something like WITHOUT REWRITE might be the way to go, though
> there are more questions: if it does not rewrite, does it scan the
> table?  Which indexes, if any, does it rebuild?  Which foreign key
> constraints, if any, does it recheck?  With patch 0, you can answer
> all these questions by enabling DEBUG1 messages and trying the command
> on your test system.  For this reason, I did consider adding a VERBOSE
> clause to show those messages at DETAIL, rather than unconditionally
> showing them at DEBUG1.  In any case, if a WITHOUT REWRITE like you
> describe covers the important question, it's certainly easy enough to
> implement.

Trouble is, only superusers can set DEBUG1.

You're right, its more complex than I made out, though that strengthens
the feeling that we need a way to check what it does before it does it,
or a way to limit your expectations. Ideally that would be a
programmatic way, so that pgAdmin et al can issue a warning.

Given your thoughts above, my preference would be for 
EXPLAIN ALTER TABLE to describe the actions that will take place.

Or other ideas... 

-- 
 Simon Riggs           http://www.2ndQuadrant.com/books/
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