Re: Timestamps and performances problems

Le Wed, 10 Apr 2002 09:27:09 -0400
"Dan Langille" <dan(at)langille(dot)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(at)langille(dot)org> me disait que :
> >
> > > On 10 Apr 2002 at 11:51, Gaetano Mendola wrote:
> > >
> > > > "Jean-Christophe ARNU (JX)" <jc(dot)arnu(at)free(dot)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".
Quel est le pb ?»
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