From: | Richard Broersma Jr <rabroersma(at)yahoo(dot)com> |
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To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Naz Gassiep <naz(at)mira(dot)net> |
Cc: | Michael Glaesemann <grzm(at)seespotcode(dot)net>, Peter Eisentraut <peter_e(at)gmx(dot)net>, pgsql-general(at)postgresql(dot)org |
Subject: | Re: Atomicity? |
Date: | 2006-08-28 20:42:13 |
Message-ID: | 20060828204213.121.qmail@web31809.mail.mud.yahoo.com |
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Lists: | pgsql-general |
> Naz Gassiep <naz(at)mira(dot)net> writes:
> > I would like more information on this deficiency and what causes it so I
> > know when to anticipate it.
>
> The uniqueness constraint is checked on a row-by-row basis, so if you
> update one row to hold the same value as another row holds, you get an
> error immediately. It doesn't matter that if the query had been allowed
> to finish, it would have updated that other row to some non-conflicting
> value. (You might be able to work around this if you could control the
> order in which rows are updated, but you can't.)
>
> This is not what the SQL spec says should happen, but so far no one has
> proposed a reimplementation that doesn't give up unreasonable amounts
> of performance. It's on the TODO list ...
Is this related to the current limitations of "SET CONSTRAINTS"?
http://www.postgresql.org/docs/8.1/interactive/sql-set-constraints.html
Regards,
Richard Broersma Jr.
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