Re: Physical Memory Fully Used and Swap is Not Used
- From: Tanel Poder <tanel@xxxxxxxxxx>
- To: moovarkku.mudhalvan@xxxxxxxxxxxxxxxx
- Date: Thu, 2 Jul 2009 01:00:38 +0300
RDA is not reporting you the full picture. Run vmstat or free instead and
see how big are the CACHED and BUFFERS field and whether there are lots &
constant page ins/outs happening.
[oracle@linux03 ~]$ vmstat 1
procs -----------memory---------- ---swap-- -----io---- --system--
-----cpu------
r b swpd free buff cache si so bi bo in cs us sy id
wa st
0 0 335728 20600 *82024 557940 *1 2 17 39 58 42 1 1
98 0 0
0 0 335728 20600 *82024 557940 *0 0 0 0 1003 187 0 1
100 0 0
In the above the free memory seems low ( I have 1GB of memory in my VM) but
the buffers & page cache figures are big and in a database server most of
pages there normally are not dirty so can be replaced & reused easily when a
process needs some physical memory.
So, on Linux you need to see how big are the buff & cache fields and whether
theres constant paging activity going on (the si / so columns) in order to
determine whether there's memory shortage or not. The "free" figure itself
doesn't tell the full story.
--
Tanel Poder
http://blog.tanelpoder.com
On Tue, Jun 23, 2009 at 8:41 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
>
>
--
Tanel Poder
http://blog.tanelpoder.com
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