Re: multiblock read count question

Hi Rob,

I think that multiblock read count only influences the optimizer. If you set it to a higher value, it is more likely that the optimizer will chosse a full table scan instead of an index access path, because it thinks table scans are very fast.
If changing multiblock read count doesn't change the execution plan of a specific SQL statement, the performance also doesn't change, since this parameter can't speed up disk reading.

"Rob K" <robkato_at_earthlink.net> schrieb im Newsbeitrag news:Qc2Y6.21823$aV1.2190988_at_newsread1.prod.itd.earthlink.net...
> Why would I be getting the same response time on full scans if the
> multiblock read count is set to 2 or 32?
>
> System:
> Oracle 8.1.7 block size 8k
>
> Sun 4500
> 2-5200 drives
> Veritas
> stripe = 4 drives with 256k interleave size = 1M stripe size.
> max i/o = 1M
>
> I change the user sessions multiblock read count to 2 and do a full scan
 on
> a table and sum up a column.
> It takes aprox 9 min to scan 60,043,128 rows 430080 blocks.
>
> I change the user sessions multiblock read count to 32 run the same query
> and it takes about the same time.
>
>
>

Ulrich Pansegrau
http://www.pansegrau-it.de Received on Wed Jun 20 2001 - 20:40:17 CDT