Re: Oracle Performance Tuning - Tips & Techniques (Possible Error found) ?

That could even be a challenge! - shame about the amount of time it would take

Regards
--
Kevin A Lewis (BOCM PAULS LTD - Animal Feed Manufacturer - Ipswich England)

                        <KevinALewis_at_HotMail.com>

The views expressed herein by the author of this document are not necessarily those of BOCM PAULS Ltd. Jonathan Lewis <jonathan_at_jlcomp.demon.co.uk> wrote in message news:933766033.11463.0.nnrp-10.9e984b29_at_news.demon.co.uk...
>
> I don't have the book, but from your description
> you certainly appear to be correct:
>
> You start with 100,000 logical I/Os of which 20,000 are physicals
> so hit ratio is 80%
>
> You add more db_block_buffers and repeat the 100,000 logical I/Os
> of which only 10,000 are physicals - if you don't do this you aren't
> testing the same case.
> so hit ratio is 90%.
>
> If the book says otherwise it is wrong.
>
> Sorry, though, you don't qualify for fallible expert
> until you discover at least 9 other errors ;)
>
>
> --
>
> Jonathan Lewis
> Yet another Oracle-related web site: www.jlcomp.demon.co.uk
>
> Kevin A Lewis wrote in message ...
> >I believe that in the genrally very good Preformance Tuning Tips &
> >Techniques, I may have found a fault.
> >
> >The calculations published on pages 154 and 155 assume that Logical Gets
> >(the sum of Consistent Gets and DB Block Gets) and Physical Reads are
> >seperate counts. In other words the total reads are sum of both. As I
> >understand it the Logical Gets are ALL the gets issued, with the Physical
> >Reads being those that have to be satisfied from disk.
> >
> >This means that the calculations published to estimate the effect of
> >increasing the DB_DATA_BUFFERS parameter subtract the hit adjustment from
> >one side of the equation and adds it to the other, rather than just
adjust
> >the number of Physical Reads.
> >
> >e.g. on the Increase side
> >NAME VALUE
> >db block gets 10000
> >consistent gets 90000 + 10000 (new logical reads added) =
> 100,000
> >physical reads 20000 - 10000 (new physical reads lost) = 10,000
> >
> >hit ratio = 1 - Physical / Logical reads x 100%
> > = (1 - (10000) / (10000 + 100000)) x 100 nb
> slightly
> >adjusted
> > = 91%
> >
> >I believe it should be more like
> >NAME VALUE
> >db block gets 10000
> >consistent gets 90000
> >physical reads 20000 - 10000 (new physical reads lost) = 10,000
> >
> >hit ratio = 1 - Physical / Logical reads x 100%
> > = (1 - (10000) / (10000 + 90000)) x 100
> > = 90%
> >
> >Please may I join the ranks of the fallible Oracle experts
>
>
>
Received on Wed Aug 04 1999 - 08:33:55 CDT