DA Morgan wrote:
> Robert Klemme wrote:
>
>>> What does cost have to do with response time?
>>> Are you looking to speed something up or is this just like "tuning the
>>> cache hit ratio".
>>
>> assumed IO cost => Plan => Performance
>>
>> where "=>" means influences.
>>
>> robert
>
> A very weak assumption. I would recommend the books written by Tom Kyte,
> Cary Milsap, and Jonathan Lewis as therapy.
I'm not sure that I would call it a very weak assumption, in fact I'd
call it really quite a good assumption. Up until very recently Oracle's
costing model was based pretty much entirely on attempting to cost
things in units of IO. Now these days there are also attempts to cost
the CPU resources being used if system stats have been gathered, but
never the less IO cost is a very large contributor to most calculated
costs, the cost drives the plan which is adopted and plan choice can
hugely influence performance.
--
Niall Litchfield
Oracle DBA
http://www.orawin.info/services
Received on Sat May 12 2007 - 14:31:21 CDT
