Re: Physical Memory Fully Used and Swap is Not Used
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_at_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_at_axa-direct.co.jp> wrote:Received on Wed Jul 01 2009 - 17:00:38 CDT
> 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.
> Mudhalvan M.M
-- Tanel Poder http://blog.tanelpoder.com -- http://www.freelists.org/webpage/oracle-l