Re: FIRST_ROWS (is is a good idea)

From: Epicentre team A <oracle_at_epicentre.fr>
Date: Mon, 2 Sep 2002 19:06:41 +0200
Message-ID: <al05g9$q9l$1@wanadoo.fr>

Thanks

I've a big request on very big tables with UNION ALL and GROUP BY. in RULE duration is nine hours
in FIRST_ROWS fifteen minutes !! (in spite of the UNION and GROUP BY clauses)
in ALL_ROWS fifteen minutes !!

curious no and very strange

i must have ... RULE nine hours, FIRST 1 hour, ALL ... 10 ou 15 minutes !!!

Bests regards
Oraclion

"Svend Jensen" <svend.jensen_at_it.dk> wrote in message news:3D73A37D.3020308_at_it.dk...
> Epicentre team A wrote:
>
> > Hello,
> >
> > Which are the dangers of FIRST_ROWS, what possible problems on my
> > datawarehouse ?
> > Oracle Version = 8.1.7.0
> >
> > Thanks
> > Oraclion
> >
> FIRST_ROWS favors index lookup and nested loop,
>
> as that generally produces the first row quick.
>
> ALL_ROWS favor hash/sort/merge joins and full/index scans,
> if hash_join_enabled=true in init.ora.
> Note that you must have a decent hash_area_size
> (memory usage for every session!). Default is twice sort_area_size.
> A bit small maybe?
>
>
>
Received on Mon Sep 02 2002 - 12:06:41 CDT