Re: WIP: Deferrable unique constraints

On Tue, 2009-07-28 at 15:15 -0400, Tom Lane wrote:
> > This might make it difficult to allow multiple constraints to use the
> > same index.
>
> Huh? That hardly seems possible anyway, if some of them want deferred
> checks and others do not.

I don't see why it's completely impossible. You could have:
* non-overlapping, deferred
* "not completely contained in", fail-early behavior

Probably not worth supporting, though.

> Sure it does. Whether the check is immediate must be considered a
> property of the index itself. Any checking you do later could be
> per-constraint, but the index is either going to fail at insert or not.

My point is that the "immediate" behavior does not require the index
itself to fail early. My original patch for generalized index
constraints has the same behavior as UNIQUE currently does (including
the fail early behavior), but can be used over indexes that know nothing
about UNIQUE (list GiST).

Regards,
Jeff Davis