RE: db_file_multiblock_read_count and performance
- From: "Post, Ethan" <Ethan.Post@xxxxxx>
- To: <Christian.Antognini@xxxxxxxxxxxx>, <ryan_gaffuri@xxxxxxxxxxx>
- Date: Tue, 7 Dec 2004 06:58:25 -0600
This kind of brings up an interesting thought. There is the script on
Ixora to test the largest MBR size and then you are suppose to set the
value to that, maybe it would be a better practice to generate a huge
table, run tests at different sizes then set. In theory the largest
size possible would be fastest but it would be interesting to find out
if this always was true. =20
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Christian Antognini
Sent: Tuesday, December 07, 2004 2:18 AM
To: ryan_gaffuri@xxxxxxxxxxx
Cc: Oracle-L@xxxxxxxxxxxxx
Subject: RE: db_file_multiblock_read_count and performance
Hi Ryan
>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.
Attached you find some results that I get during some tests that I
performed on different servers by different customers (notice that I had
no influence on the setup, I just run a test script...).
As you can see many different behaviors are to be expected.
System 1: higher values are better, of course they are "technical"
limits... (notice that 55MB/s is the maximum throughput measured on this
system, i.e. with DFMRC=3D32).=20
System 2: values higher than 16 give bad performance, i.e. the optimal
value is 16.
System 3: values less than 17 are useless, i.e. at least 17 should be
used to have "correct" performance.
System 4: no performance difference was measured. Notice that this
system, with 230MB/s, is also the faster I tested...
HTH
Chris
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