Re: buffer hit cache ratio

"Niall Litchfield" <n-litchfield_at_audit-commission.gov.uk> wrote in message news:<3ff006d8$0$13343$ed9e5944_at_reading.news.pipex.net>...
> "JEDIDIAH" <jedithezealot_at_yahoo.com> wrote in message
> news:5121813f.0312261236.4c0d3220_at_posting.google.com...
> > If you have hardware resources, you should make sure you're exploiting
> > them properly. This means configuring your SGA accordingly as well as
> > ensuring OS, applications and storage hardware similarly well configured.
>
> For some reason I'm reminded of Windows, look loads of CPU,RAM and DISK lets
> use it all... I'm sure that isn't what is intended, but when new servers
> come with 4-16gb of RAM as standard why pick an SGA size of 1.5 - 6gb just
> because the resources are there.
>
> > The BHCR isn't a silver bullet, just part of a long laundry list of
> > things to check. Of course if it were completely meaningless, Oracle
> > would leave it out of the statspack report. '-)
>
> So 'tuning' is a process of box ticking? BCHR > 80% tick, LCHR > 99.5% tick,
> DBA salary > $70k tick etc etc. Tuning ought to be about finding what is
> causing your key processes to perform inadequately and improving them -
> running through a checklist just isn't as effective as focussing on response
> time.

Isn't it a process of box ticking to _get_ you to the point of being able to focus on response time? Surely you aren't advocating starting with a default SGA on a new 6G system, when you have experience with a smaller system running similar stuff. Don't you set parameters to where you think they ought to be and then test? Even myths can be useful ROT.

Maybe I just have skewed experience of not being hired into well-run systems, but most existing systems I've encountered have been way off.  Some of that is undoubtedly due to the clueless not going past the box ticking, but a lot has been due to the fundamental configuration never being correctly administered. In some cases, due to bizarro 3rd-party vendor recommendations. In some cases, due to the inexperienced learning on the job. In most cases, due to management not understanding or caring about proactive DBA work.

jg

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