• From: Frits Hoogland <frits.hoogland@xxxxxxxxx>
  • To: lambu999@xxxxxxxxx
  • Date: Tue, 6 Jul 2010 13:49:19 +0200


Jonathan Lewis has a good blogpost about this: 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.

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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