Re: Clarification, please

[Mladen Gogala <mladen(dot)gogala(at)vmsinfo(dot)com>]

Tom Lane wrote:
> 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 ...
>   

I humbly admit being one. I am getting used to the life without the dark 
side of the force, however. I saw the light, I am saved. When the 
rapture comes, I will not be left behind.  However, I still have to 
maintain a rather big 4-way Oracle RAC configuration and some satellite 
Oracle databases.

>   
> > 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.
>   

I agree with you. I was only wandering how was it done with a unique index.

> 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
>   
Thanks for a wonderful explanation. That's all I needed.

--

Mladen Gogala 
Sr. Oracle DBA
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