Mladen Gogala <mladen(dot)gogala(at)vmsinfo(dot)com> writes:
> In Oracle, deferrable primary keys are enforced by non-unique indexes. 
> That seems logical,

... maybe to an Oracle guy ...

> When the constraint is deferred in the transaction block, however, it 
> tolerates duplicate values until the end of transaction:

Sure.  That's exactly per spec: the check is deferred to end of
transaction.  If the duplicated index entries are both/all still live
at that time, you get an error.

We do still execute the insertion-time uniqueness check, but instead of
throwing an error on failure, we just queue a trigger event to recheck
that key before commit.  If the insertion-time check passes then there's
no need for a recheck later.  This is a win because the insertion-time
check is cheap, being integrated into the insertion process itself.

			regards, tom lane

In response to

• Clarification, please at 2010-12-01 16:49:02 from Mladen Gogala

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• Re: Clarification, please at 2010-12-01 17:28:17 from Mladen Gogala

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