On 10 Apr 2002 at 10:44, JX wrote: > Le Wed, 10 Apr 2002 09:27:09 -0400 > "Dan Langille" <[EMAIL PROTECTED]> me disait que : > > > On 10 Apr 2002 at 9:13, JX wrote: > > > > > Le Wed, 10 Apr 2002 09:06:55 -0400 > > > "Dan Langille" <[EMAIL PROTECTED]> me disait que : > > > > > > > On 10 Apr 2002 at 11:51, Gaetano Mendola wrote: > > > > > > > > > "Jean-Christophe ARNU (JX)" <[EMAIL PROTECTED]> 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?
If there is an index on that field, casting to a timestamp may help the optimization. Therefore I suggested that it be tried. -- Dan Langille The FreeBSD Diary - http://freebsddiary.org/ - practical examples ---------------------------(end of broadcast)--------------------------- TIP 6: Have you searched our list archives? http://archives.postgresql.org
