Re: ALTER TABLE ... ALTER COLUMN ... SET DISTINCT

Robert Haas escribió:
> On Sat, Apr 4, 2009 at 7:04 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> > Robert Haas <robertmhaas@gmail.com> writes:
> >> Per previous discussion.
> >> http://archives.postgresql.org/message-id/8066.1229106059@sss.pgh.pa.us
> >> http://archives.postgresql.org/message-id/603c8f070904021926g92eb55sdfc68141133957c1@mail.gmail.com
> >
> > I'm not thrilled about adding a column to pg_attribute for this.
> > Isn't there some way of keeping it in pg_statistic?
> 
> I don't like the idea of keeping it in pg_statistic.  Right now, all
> of the data in pg_statistic is transient, so you could theoretically
> truncate the table at any time without losing anything permanent.

Maybe use a new catalog?

> What is the specific nature of your concern?  I thought about the
> possibility of a distributed performance penalty that might be
> associated with enlarging pg_attribute, but increasing the size of a
> structure that is already 112 bytes by another 4 doesn't seem likely
> to be significant, especially since we're not crossing a power-of-two
> boundary.

FWIW it has been said that whoever is concerned about pg_attribute bloat
should be first looking at getting rid of the redundant entries for
system columns, for each and every table.

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support