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Re: PGA_AGGREGATE_TARGET formula

Richard Foote

2004-08-24

Replies:
Hi Syed,

It's a totally meaningless formula. Totally.

What governs how much PGA you require ? Two things. The total *number* of
concurrent sessions and what those sessions *do*. If your OLTP database runs
relatively few pieces of "code" on a small subset of data but requires
thousands of concurrent sessions, then it's quite conceivable you'll need a
significant proportion of your memory for PGA, more so than SGA. In fact,
large numbers of concurrent sessions will require mucho PGA, period.

Therefore, any "formula" that doesn't consider the concurrent activity of
the database is useless ...

One OLTP database I look after has approx. 50% memory for PGA, another has
5%. Go figure ?

The below quote was written by the same person that said a family requires a
house with 20% space for bedrooms and 80% for living space. Ask our
neighbours with 11 children to comply with the above "formula".

You get the picture.

Cheers

Richard
----- Original Message -----
From: <SJHussain@(protected)>
To: <oracle-l@(protected)>
Sent: Tuesday, August 24, 2004 6:29 PM
Subject: PGA_AGGREGATE_TARGET formula

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?

Best Regards,

Syed Jaffar Hussain


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