Re: Timestamps and performances problems

Le Wed, 10 Apr 2002 09:27:09 -0400
"Dan Langille"  me disait que :

> On 10 Apr 2002 at 9:13, JX wrote:
> 
> > Le Wed, 10 Apr 2002 09:06:55 -0400
> > "Dan Langille"  me disait que :
> > 
> > > On 10 Apr 2002 at 11:51, Gaetano Mendola wrote:
> > > 
> > > > "Jean-Christophe ARNU (JX)"  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() - '1 hour'::interval)
> > > 
> > > Try where 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
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