Re: Sequences/defaults and pg_dump

On 2/7/06, Martijn van Oosterhout <kleptog(at)svana(dot)org> wrote:
> On Tue, Feb 07, 2006 at 02:33:56PM +0300, Nikolay Samokhvalov wrote:
<snip>
> Well, it's a very contrived example (I can't think of a reason why one
> would do that) but I agree it is a bug. You could acheive the same
> effect by setting the step of the sequence to 10.

'* 10' is just an example.
The real situation would be as the following.
I want to use some algorithm to hide real number of registered users
in my table user. So, I don't want to use simple sequence, when every
new registered user in my system can guess what is the number of
registered users simply observing his ID. So, I use following
algorithm:
(nextval('...name of the sequnence...') * N) mod % M,
where N and M are quite big numbers that have no common multiples
besides 1 (sorry, do not remember the English term for those numbers
;-) ).

> > For me as end-user this is very-very strange and I consider it as
> > 'gotcha' of PosgreSQL.
>
> Well, I would hardly call the latter a gotcha, given you're probably
> the first person to notice it. As for the first question, I'm not sure
> what you expect. SERIAL has always just been a sort of macro, so I
> don't see how this could be changed.

I wonder why people didn't notice this bug earlier, but I'm sure that
there are many situations when it could be revealed. For example, what
if I want to use nextval('seq1') * nextval('seq2') ?.. I'm sure that
if you think you'll discover new examples that would be used in real
world.

Anyway, this is a bug, and I'll write the bug report to bugs mailing list.

>
> Have a nice day,
> --
> Martijn van Oosterhout <kleptog(at)svana(dot)org> http://svana.org/kleptog/
> > Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a
> > tool for doing 5% of the work and then sitting around waiting for someone
> > else to do the other 95% so you can sue them.
>
>
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--
Best regards,
Nikolay