Re: Timestamps and performances problems

Le Wed, 10 Apr 2002 09:27:09 -0400
"Dan Langille" <dan@langille.org> me disait que :

> On 10 Apr 2002 at 9:13, JX wrote:
>
> > Le Wed, 10 Apr 2002 09:06:55 -0400
> > "Dan Langille" <dan@langille.org> me disait que :
> >
> > > On 10 Apr 2002 at 11:51, Gaetano Mendola wrote:
> > >
> > > > "Jean-Christophe ARNU (JX)" <jc.arnu@free.fr> wrote:
> > > > > Hello all.
> > > > >   I've a performance problem on specific requests :
> > > > >
> > > > >   When I use timestamps + interval in where clauses, query
> > > > >   performance is slowed down by a factor of 20 or 30!!!! For exemple
> > > > >   : select timestamp,value
> > > > >   from measure
> > > > >   where timestamp<now() and timestamp>(now() - '1 hour'::interval)
> > >
> > > Try where timestamp<now() and timestamp>(now() - '1
> > > hour'::interval)::timestemp.
> >
> >     What's the difference with the syntax above? It takes he same time
> >     than the query above. Bounded timestamps with "real" ISO timestamps
> >     strings are always up to about 200 times faster (with extensive test
> >     proof).
>
> It casts the value to a timestamp.  I would prefer to discuss this on-
> list.
    Okaye, but what's the incidence on preformance issues?
    Casting should only insure that given string is to be taken as a timestamp
isn't it? Does it make an "instanciation" of the timestamp to be that would be
applied for comparision clauses?

    Thanks

--
Jean-Christophe ARNU
s/w developer
Paratronic France
«Dès que je clique sur "mount", il ne fait rien et le cdrom
 reste "unmount".
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