Re: performance issue on select count(*)

So, what exactly is indicated by a high or low hit rate? What, exactly, is "high" and what do you consider "low"?
What "HR" are you talking about?
This would be the infamous BCHR:

select 'bc_hit_ratio' ratio,( sum(decode(name, 'consistent gets',value,0)) + sum(decode(name,'db block gets', value,0)) - sum(decode(name,'physical reads', value,0))) / ( sum(decode(name, 'consistent gets',value,0))   + sum(decode(name,'db block gets', value,0)) ) * 100 from v$sysstat

What exactly should the number returned by this query tell me?

On 10/28/2003 10:59:25 AM, Binley Lim wrote:
>
> The symptom suggests caching is a big factor here - most likely
> block-buffers.
>
> Contrary to ?current? popular beliefs, BCHR is still a very relevant
> performance indicator - either being very high, or being too low - both of
> which gives a good indication of something that needs to be looked at.
>
>
> > I would be interested to know if there is a way to speed up the initial
> > execution or how to diagnose what the delay was. It does not seems right
> > that there is such a big difference in elapsed time between the initial
> and
> > subsequent execution.
>
>
> --
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> --
> Author: Binley Lim
> INET: Binley.Lim_at_xtra.co.nz
>
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Mladen Gogala
Oracle DBA

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-- 
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-- 
Author: Mladen Gogala
  INET: mladen_at_wangtrading.com

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