> On Saturday 14 July 2001 02:49, Tom Lane wrote:
>
> > >
> > > It would seem that Oracle's execution plan is more optimal.
> >
> > Hmm, since I don't know the details of Oracle's plan displays, it's hard
> > to comment on that --- but it looks to me like the plans are essentially
> > the same, with the small difference that Postgres chooses to use the
> > index on dim0 to filter ....(snipped )
>
> After a little thinking, I am inclined to agree with you Tom... I wondered if
> the difference might to be due to pure sequential scan performance
> differences. I tried this query :
>
> SELECT sum(val) FROM fact0
>
> for Postgres, Db2 and Oracle. The results were
>
> Postgres 2m25s
> Db2 40s
> Oracle 50s
>
> This seems to be the likely culprit. I suspect that the "many block/page read
> at once" type optimzations (prefetch for Db2 and mutli block read for Oracle)
> mean that table sequential scans are faster for these guys than Postgres.
>
> Thus on the bright side their access plans are not necessarily any better
> than Postgres !
Can you remind me about the OS you are using?
--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
