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Re: FIRST_ROWS (is is a good idea)

From: Richard Foote <richard.foote_at_bigpond.com>
Date: Mon, 2 Sep 2002 23:31:37 +1000
Message-ID: <WBJc9.22127$g9.65983@newsfeeds.bigpond.com>

Hi Epicentre,

I would suggest all things being equal, for a data warehouse environment, the FIRST_ROWS optimizer option would NOT be recommended.

Commonly in data warehouse applications, the ploughing through and the summarisation of large volumes of data is the norm. Therefore an execution plan that returns the first row as efficiently as possible is unlikely to be the most efficient. FIRST_ROWS strongly favours the use of indexes and nested loop joins which may not be appropriate.

9i provides various flavours of first_rows which provides more flexibility.

As always, study the execution plan generated by important SQL and tune as necessary (which may involve switching the optimizer modes as necessary) although I would suggest ALL_ROWS would be your best bet.

Cheers

Richard
"Epicentre team A" <oracle_at_epicentre.fr> wrote in message news:akvo3h$338$1_at_wanadoo.fr...
> Hello,
>
> Which are the dangers of FIRST_ROWS, what possible problems on my
> datawarehouse ?
> Oracle Version = 8.1.7.0
>
> Thanks
> Oraclion
>
>
>
Received on Mon Sep 02 2002 - 08:31:37 CDT

Original text of this message

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