RE: db_file_multiblock_read_count and performance
- From: "Cary Millsap" <cary.millsap@xxxxxxxxxx>
- To: <Oracle-L@xxxxxxxxxxxxx>
- Date: Mon, 6 Dec 2004 11:44:26 -0600
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
* Nullius in verba *
Upcoming events:
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-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx =
[mailto:oracle-l-bounce@xxxxxxxxxxxxx]
On Behalf Of ryan_gaffuri@xxxxxxxxxxx
Sent: Monday, December 06, 2004 11:21 AM
To: Oracle-L@xxxxxxxxxxxxx
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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