Re: Forcefully adding a CHECK constrained

On Tue, 2012-05-15 at 12:52 +0300, Catalin(ux) M. BOIE wrote:
> The old_stats is so big that I cannot afford to add a check constraint.
> But, I know that all values of the itime field are before 2012_04, so,
> would be great if I could run something like:
>
> ALTER TABLE old_stats ADD CONSTRAINT xxx CHECK (itime < 2012_04_timestamp)
> FORCE;
>
> I never looked at PostgreSQL sources, but the commit
> Enable CHECK constraints to be declared NOT VALID
> http://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=897795240cfaaed724af2f53ed2c50c9862f951f
> inspired me to dive.
> Is PostgreSQL's team willing to accept such a feature?

It looks like you already found the answer! Create the constraint using
NOT VALID, and then sometime later (when you can afford the full scan)
do a VALIDATE CONSTRAINT.

Unfortunately, this is only available in 9.2, which is still in beta.

http://www.postgresql.org/docs/9.2/static/sql-altertable.html

CHECK constraints don't use indexes, so CREATE INDEX CONCURRENTLY
doesn't help you.

Regards,
Jeff Davis