Memory Question

Parekh, Ketan KParekh at maxis.com
Wed Jul 28 22:21:29 UTC 2004


As a general rule of thumb how much memory should be left for the OS ?

Assuming I have 4 GB physical memory ?

Thanks
Ketan

-----Original Message-----
From: redhat-list-bounces at redhat.com
[mailto:redhat-list-bounces at redhat.com] On Behalf Of Tobias Speckbacher
Sent: Wednesday, July 28, 2004 2:31 PM
To: General Red Hat Linux discussion list
Subject: RE: Memory Question



Looking at your kernel version you are using AS2.1.
The only parameters you should have had to change are shmmax, sem
,shmall, semmni (some of the default are acceptable)
The commands indeed should return the correct output.

The OS should be using far less than 500MB.

As you can see in the info you posted.

Free: 154764
Buffers: 333072
Total "free" = 476MB

So OS memory used should be 4GB - 476MB - SGA - PGA

In any case an SGA this large with 4GB memory will cause issues as you
start using the DB from my experience.

-Tobias

-----Original Message-----
From: redhat-list-bounces at redhat.com
[mailto:redhat-list-bounces at redhat.com] On Behalf Of Parekh, Ketan
Sent: Wednesday, July 28, 2004 12:07 PM
To: redhat-list at redhat.com
Subject: Memory Question

HI! Folks,

 

I need some help with memory stats. I have an Oracle database running. 

Below is he OS version : 

Linux tsonode1 2.4.9-e.25enterprise #1 SMP Fri Jun 6 17:55:13 EDT 2003
i686 unknown

 

oracle at tsonode1[tsodev1]$ free -t

                     total         used       free     shared    buffers
cached

Mem:       2058760    1814816     243944     742204     243924
213272

-/+ buffers/cache:      1357620     701140

Swap:      2096472     217516    1878956

Total:     4155232      2032332    2122900

 

>From the above as to what I understand is 

Total Physical memory is : 2 GB

USED                               1.35 GB is used

Free                                  701 Megs

 

So of the 1.35 used 

Oracle SGA is                             950 Megs

Oracle PGA ( Process memory )  260 Megs

Other non-oacle process             150 Megs

                        Total                 1.35 GB

 

Now there is a limitation on RH 2.1 Advanced server for having oracle
SGA > 1.8 GB. To increase the SGA we had to 

Changes to the memory settings and relinked the oracle binaries as
explained in the RH doc. 

 

OS : Linux tsonode2 2.4.9-e.46enterprise #1 SMP Wed Jun 30 18:11:26 EDT
2004 i686 unknown

 

                     total       used       free     shared    buffers
cached

Mem:       3863184    3708420     154764    2461228     333072
587348

-/+ buffers/cache:       2788000    1075184

Swap:      2096472       1116    2095356

Total:       5959656    3709536    2250120

 

SGA                  : 2.75 GB

PGA                  : 837 Megs

 

Total Physical memory is 4 GB on ths host.

 

So now the confusion part is is Oracle has sucked in 2.75 + 537 = 3.5 GB
- is the OS using only 500 megs ?

Does free -t , top vmstat commands show the right numbers after this
change in the kernel ?

 

BTW : both the free -t outputs are from diff nodes - I put them to
compare and see where am I going wrong here.

 

Thanks for your help..

 

Ketan

 

 

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