RE: db_file_multiblock_read_count and performance

A parameter like this has some effects that range beyond what you may be testing. One issue with changes to db_file_multiblock_read_count that = people
sometimes neglect is that its value is an input to the Oracle cost-based query optimizer. In other words, changing its value can change execution plans in parts of your application that are completely outside your span = of
consideration when you're thinking about the potential impact of your proposed change. This produces the result that, in effect, "changing = dfmrc
causes a significant different in performance." ...But not for the = reasons
that will be illustrated by your tests.

Cary Millsap
Hotsos Enterprises, Ltd.
http://www.hotsos.com
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-----Original Message-----
From: oracle-l-bounce_at_freelists.org =
[mailto:oracle-l-bounce_at_freelists.org]
On Behalf Of ryan_gaffuri_at_comcast.net
Sent: Monday, December 06, 2004 11:21 AM To: Oracle-L_at_freelists.org
Subject: db_file_multiblock_read_count and performance

I have been testing this extensively over the last few months. I do a = full
table scan with a db_file_multiblock_read_count =3D 1 and then one =3D = 128( i
check the 10046 trace to verify i am getting this much) and I see = absolutely
no difference whatsoever in response time.=20 i am doing=20
select count(*)
from heap_table;
I have tested this on windows xp, solaris, with EMC, netapp, and regular = old
cheap off the shelf hard drives. I have tested it in 8.1.7, 9.0,9.1,9.2. has anyone see a response time improvement from this parameter anywhere? =

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