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Home -> Community -> Mailing Lists -> Oracle-L -> 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£º 9 am ¨C 15pm.
Oracle: 5% increase.
Unix: 6% increase.
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