Re: Cache Hit Ratio from system views

"Niall Litchfield" <niall.litchfield_at_dial.pipex.com> wrote in message news:IbqdnWec9fPPyEXbnZ2dnUVZ8tWnnZ2d_at_pipex.net...
> Bob Jones wrote:
>> No, you either have not read all the threads or make no effort to
>> understand
>> my point.
>
> I have read and read your posts Bob. You've stated that the BCHR ratio
> tells you the disk IO percentage which is sort of true - though it
> rather begs the question of what you understand by disk since strictly
> it tells you the ratio of IO that Oracle obtains from it's own cache to
> that which it has to make filesystem IO calls for, and on lots of
> installations a filesystem call won't come from disk at all.
>

I have no problem with that argument if you like to talk about database and OS together, but to get a clear view you must isolate performance factors. If you don't no metric out there will have any meaning. There are also poeple using raw and dio.  .
>> I will wait unitl you get into an objective mindset, or am I being too
>> optimistic.
>
> If the BCHR is an objective indicator, please tell us of what you think
> it is an indicator, and how - specifically you would use it. Richard's
> indicator (as mine) is how long business transaction take. Definitely
> objective and relatively straightforward to use and understand.
>
>

BHCR shows disk i/o percentage. An important indicator for buffer cache tuning.
As I said before, response time is not even a database metric. It is an effect not a cause. With some people's logic here, even response time is meaningless. 5 minutes response time can be better than 5 seconds response time, if it is doing 5000 times more work. Received on Fri Aug 31 2007 - 19:29:53 CDT