An unusually high BCHR could be an indicator that your database
is running Connor McDonald's choose_a_hit_ratio procedure.
http://www.oracledba.co.uk/tips/choose.htm
Jared
| Mladen Gogala <[EMAIL PROTECTED]>
Sent by: [EMAIL PROTECTED] 10/28/2003 09:09 AM
|
To: Multiple recipients of list ORACLE-L <[EMAIL PROTECTED]> cc: Subject: 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.
>
>
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.net
> --
> Author: Binley Lim
> INET: [EMAIL PROTECTED]
>
