Re: OPTIMIZER MODE
- From: Frits Hoogland <frits.hoogland@xxxxxxxxx>
- To: lambu999@xxxxxxxxx
- Date: Tue, 6 Jul 2010 13:49:19 +0200
Ram,
Jonathan Lewis has a good blogpost about this:
http://jonathanlewis.wordpress.com/2008/11/11/first_rows_n/. Randolf Geist has
also done a presentation on FIRST_ROWS (actually FIRST_ROWS_n to be precise) on
last year's UKOUG.
In essence:
a) general advise is to use ALL_ROWS, unless your system generally only uses
the first rows the query returns. Most systems use the entire query resultset.
b) if you already have your system running on FIRST_ROWS, a change of optimizer
mode will impact your entire system, so not just change it.
frits
On Jul 6, 2010, at 1:17 PM, Ram K wrote:
> Listers,
>
> We have a new 11g based hybrid application that a third party vendor is
> configuring. We observe some slowness in the response times. I do not see any
> slow sql in v$sql. The vendor is recommending that we set the OPTIMIZER_MODE
> to FIRST_ROWS to get better response times, among other parameter changes. I
> have read in few sources that FIRST_ROWS is not generally used, with oracle
> itself using ALL_ROWS. Can anyone advise?
>
> --
> Thanks,
> Ram.
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