Re: *****SPAM***** Re: I/O and db_file_multiblock_read_count

Ahh, you're right. I must've misinterpreted that somewhere.

Thanks for the update!

Stefan

On 12/9/06, Wolfgang Breitling <breitliw_at_centrexcc.com> wrote:
>
> At 01:44 AM 12/9/2006, Stefan Knecht wrote:
> >The thing is, when you collect system statistics (aka make use of
> >cpu costing) - Oracle gathers stats about your systems' average
> >multiblock read count. It then uses that information instead of
> >whatever you might have set in your init.ora.
> >
> >Therefore, his test may be wrong - IF he's got sysstats.
>
> That is not correct. Kevin's test is independent of whether he has
> system statistics or not. System statistics come into play only
> during the CBO's parse phase. If system statistics are in place then
> the CBO during parsing will use the MBRC value of the system
> statistics to calculate the cost of full scans, but Oracle's
> execution engine will use the db_file_multiblock_read_count value
> when doing full scans. That is one of the beauties of system
> statistics - you can use the OS' full IO bandwidth without messing up
> the CBO's cost calculation for full scans.
>
>
> Regards
>
> Wolfgang Breitling
> Centrex Consulting Corporation
> www.centrexcc.com
>
>
>

--
http://www.freelists.org/webpage/oracle-l