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Re: buffer hit cache ratio

From: JEDIDIAH <jedithezealot_at_yahoo.com>
Date: 26 Dec 2003 12:36:52 -0800
Message-ID: <5121813f.0312261236.4c0d3220@posting.google.com>


rgaffuri_at_cox.net (Ryan Gaffuri) wrote in message news:<1efdad5b.0312230511.9972d23_at_posting.google.com>...
> pharfromhome_at_hotmail.com (Geomancer) wrote in message news:<cf90fb89.0312221936.14869401_at_posting.google.com>...
> > > Tuning by the BCHR is not done by today's top Oracle professionals.
> >
> > Depends on who you consider a "top" professional.
> >
> > Tom Kyte and Cary Millsap both argue that the BHR is not a panacea,
> > but is IS useful for detecting when the data buffers are way too
> > small.
> >
> > The BHR is VERY similar to the v$db_cache_advice view.
>
> that is not accurate. milsap is active on oracle-l_at_fatcity.com. He has
> repeatedly said that BHCR is only useful to tell you if you have alot
> of very bad sql. Namely if its VERY high, you have alot of terrible
> sql.

This is simply a naieve overgeneralization. The quality of your sql is quite independent of your BHCR. Each can be tweaked independent of the other.

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.

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. '-)

>
> Kyte says the only ratio he uses is parse/execute. Its in both of his
> books and i believe on his website.

Unnecessary disk IO is going to slow a system down remarkably faster than unnecessary cpu activity.

[deletia] Received on Fri Dec 26 2003 - 14:36:52 CST

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