RE: see higher CPU usage after increase SGA
- From: "Bobak, Mark" <Mark.Bobak@xxxxxxxxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Wed, 9 Jun 2004 10:56:11 -0400
Zhu,
Consider that possibly your CPU usage was being throttled by the disk I/O, and
by reducing disk I/O, you allow Oracle to do more work, hence consume more CPU.
You mentioned that transactions were the same from one snapshot to the other,
but that doesn't count SELECT statements. Try also comparing logical
reads/sec. How do those numbers compare? What about Parse CPU?
-Mark
Mark J. Bobak
Oracle DBA
ProQuest Company
Ann Arbor, MI
"Post Hoc Ergo Propter Hoc"
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On
Behalf Of zhu chao
Sent: Wednesday, June 09, 2004 9:31 AM
To: oracle-l@xxxxxxxxxxxxx
Subject: see higher CPU usage after increase SGA
Hi,
I once saw Jonathan said at metalink that huge SGA does not help in many
case, But no further discuss at that topic later. Last night we added 1Gb
to oracle sga and we see fewer disk read but higher CPU usage.
Fewer disk read of course cut CPU usage, but larger buffer cache
management in unix and oracle, seems caused higher CPU usage. Has someone
also have similar experience? How to explain the higher CPU usage?
We have a 16GB memory sun 880 with 10G data cache. As disk read get
higher and higher , and not much SQL to tune we deciede to increase data
buffer from 10G to 11GB, as there is still 1.5G free memory on the host.
We expect to see some CPU usage drop, as disk read drop by 30%. But
after 1 day's run, we saw higher CPU usage then before we increase the SGA.
http://www.cnoug.org/attachments/LDBn_cpu.bmp (the Excel picture that
shows the CPU usage before and after increase sga).
The following Statistics from Oracle shows the load profile before and
after SGA increase:
LIO PIO Transaction/Second
CPU usage in oracle
10gb 47,990.70 448.68 76.54
177.9
11gb 47,707.28 325.95 76.54
187.9
Change: Nearly same Disk read dropped Transaction rate
CPU used increased.
30% keep consistent
by 5%
Time I measure： 9 am - 15pm.
Oracle: 5% increase.
Unix: 6% increase.
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