Re: Deferrable Unique Constraints

Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:

> Yeah, what I've been visualizing is a list of "tentative duplicates" ---
> that is, you do the immediate unique check same as now, and if it passes
> (which hopefully is most of the time) then you're in the clear.

I don't see how you're in the clear. If session A does an insert and it
doesn't see a duplicate and doesn't commit, but then B does an insert and sees
the duplicate from A and marks his tentative, and then commits, shouldn't B's
commit succeed? Then when A commits shouldn't his fail? So A still has to
recheck even if there was no sign of a duplicate when he inserted.

Unless there's some way for B to indicate to A that his insert has become
tentative then I think you have to resign yourself to checking all deferred
unique constraints, not just ones that seem suspect.

--
greg