Re: linux memory: limiting filesystem caching
- From: zhu chao <zhuchao@xxxxxxxxx>
- To: Christo Kutrovsky <kutrovsky.oracle@xxxxxxxxx>
- Date: Wed, 13 Jul 2005 22:55:55 +0800
Hi,
Actually system has been down for almost one year and I have lost
the statistics. I remember I checked SAR log to compare user%, SYS%
CPU usage. I can't find significant difference.
As for memory, I check free log (I have cronjob to report memory
usage to log file). My system used middleware and we don't have often
connect-disconnect behavior. I don't have system hung (once actually
during the 2 year's this RAC system lifecycle, unknown reason, 7445
and system panic). We don't do heavy filesystem IO operation. I have
1.7GB sga and 4GB physical memory.
>and if your sessions
> are touching the entire SGA,
I don't understand this. Every session, would access the whole SGA on
its session creation. right?
I was the very early user of oracle 9.2 RAC user and did play some
so-called tuning at OS level, painfully I did not see much performance
gain, including those network, kernel parameter tuning. One
significant thing is max open file must be increased else when session
connections high, oracle unable to open file.
On 7/13/05, Christo Kutrovsky <kutrovsky.oracle@xxxxxxxxx> wrote:
> Zhu,
>
> How did you measure the performance differences when using bigpages
> and not using them? What kind of tests did you run ? Were they CPU or
> disk IO specific ? Do you have statistics of CPU usage in "user" mode
> and "system" mode?
>
> We have at least 3 cases where converting a production system to
> bigpages/hugepages was the difference between a hung system and a well
> performing system.
>
> As for memory savings, what counter-arguments do you have? Keep in
> mind that PTE pointers are allocated as needed, and if your sessions
> are touching the entire SGA, for example as often happens, they
> reconnect often.
>
> I agree that it doesn't sound reasonable, thus the hugepages solution.
>
>
> --
> Christo Kutrovsky
> Database/System Administrator
> The Pythian Group
--
Regards
Zhu Chao
www.cnoug.org
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