Re: Physical Memory Fully Used and Swap is Not Used
- From: LS Cheng <exriscer@xxxxxxxxx>
- To: moovarkku.mudhalvan@xxxxxxxxxxxxxxxx
- Date: Wed, 24 Jun 2009 08:44:21 +0200
Hi
In the IO side you should enable direct i/o and aio in Linux (if you are
using filesystems).
In the memory side you should enable hugepages, this is a nonswappable
memory, i.e all SGA will be in physical memory. Be careful when setting this
up though, some miss calculations will make Oracle use normal pages.
Regarding Linux uses all memory, that behaviour is default behaviour for
ages, Linux tries to cache everything and uses all memory. Why leave memory
free when you can use it, I think that is philosophy. There were some kernel
parameters to change this behaviour but since Linux changes pretty fast and
I cant really tell you if they still work in your Linux platform. Last time
I checked they were working for RHEL 4 but no longer in RHEL 5 and I cant
find the corresponding kernel parameters in RHEL 5 :-(
About your performance problem I think you better identify them first inside
database (look some statspack or AWR if you have license). If Swap is not in
use then the OS is not swapping, if there are heavy swap going on in Linux
kswapd kicks in, in heavy memory starvation system when kswapd wakes up and
freeing memory it hangs the system too! :-)
Thanks
--
LSC
On Tue, Jun 23, 2009 at 7:41 AM, Mudhalvan Moovarkku <
moovarkku.mudhalvan@xxxxxxxxxxxxxxxx> wrote:
> Dear DBAs,
>
> We have recently migrated Oracle from 8.0.6 on HP-Unix to 10.2.0.4
> on Red Hat Linux
>
> Earlier the same application worked fine with 7GB RAM on HP-UNIX
> on PA-RISC
>
> Upgraded system on IBM X 3850 with 16GB RAM but still we have some
> performance issue.
>
> I knew there is some lagging because of Hardware Architecture but
> it is too bad 7 GB to 16GB RAM but still have performance.
>
> Please look at data collected from RDA. Looking at this scenario
> my physical memory is fullly used but Swap is not at all used.
>
> Total Physical Memory 16032 MiB
>
> Available Physical Memory 30 MiB
>
> Swap: Max Size 24575 MiB
>
> Swap: Available 24505 MiB
>
> Swap: In Use 70 MiB
>
> We know there is some performance issue in application. I would
> like to make as much as possible from Database/Linux side tunning to
> provide atlease peaceful performance. Can any body through some light on why
> the swap is not at all used.
>
> Regards
>
> Mudhalvan M.M
>
>
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