Re: PGA_AGGREGATE_TARGET formula

On Tue, 24 Aug 2004 11:29:33 +0300, sjhussain_at_alfransi.com.sa <sjhussain_at_alfransi.com.sa> wrote:
>
>
> Gents,
>
> I was just read Oracle Metalink Note 223730.1 Automatic PGA Memory
> Management in 9i. There is a recommended formula for setting PGA on OLTP
> and DSS systems. I am interested in OLT system only.
> For OLTP the folurma is PGA_AGGREGATE_TARGET = (<Total Physical Memory> *
> 80%) * 20%
>
> I just want to ask you people, how accurate is this formula?

It isn't 'accurate' it is a way of picking a starting value for P_A_T, It seems perfectly adequate for this purpose. The meat of the note is in stage 2 where it gives you some steps for monitoring the behaviour of your system and adjusting the value accordingly, as well as details of what P_A_T is actually doing.

For what its worth it seems to me that the first assumption (that only 80% of the system memory is available to Oracle ) seems fine. The second part, that you should allocate 20% of what is available to PGA (and presumably 80% to SGA ) for OLTP and make the split 50/50 for DW seems entirely arbitrary.

The unstated assumption I suppose behind all of it is that the total physical memory available is sized in some intelligent way.

-- 
Niall Litchfield
Oracle DBA
http://www.niall.litchfield.dial.pipex.com
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