Re: multiblock read count question

In particular if you are using raw, you can get a large amount of gains from increasing this value - its not just an optimiser thing

hth
connor

--
==============================
Connor McDonald

http://www.oracledba.co.uk

"Some days you're the pigeon, some days you're the statue..."
"Ulrich Pansegrau" <das_hirn_at_freakmail.de> wrote in message
news:3b314fcc$0$29845$9b622d9e_at_news.freenet.de...


> 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

>

>