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/PostgreSQL Development, 24x7 Support, Training and Services
