Re: Physical Memory Fully Used and Swap is Not Used

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

Other related posts: