SAP and memory Management

[Former Member]

Hi Experts,

I have gone through Memory management link on help.sap.com, but i have un-resolved doubts , so i guess you people could help me.

In ST06 there is Physical Memory and Swap . IS it equivalent to Shared Mem+local Mem = Physical + Swap?

In ST02 there is tab storage : In that

there is a line Virtual memory allocated total ............KB

Is this total memory allocated to SAP ? and is it allocated from Physical+Swap or only Physical?

Size of extended memory ..........KB . Is this too allocated from Physical+Swap or only Physical or only Swap ?

parameter em/initial_size_MB i think only limits the total usage of extended memory by all wp , am i right?

If yes then this parameter can be increased till amount of physical or physical+swap?

At OS level i hit command Top and i checked mem utilization for my session...it was 7GB

3 ? 2874 root 154 20 7848K 820K sleep 313:44 0.17 0.17 sendmail:

3 ? 6605 sidadm 155 20 7674M 178M sleep 168:22 0.17 0.17 dw.sapSID_DVEBMGS$$

I checked in SM04 and data obviously did not match as the EM usgae was just 10MB(10.039.740 B).

So i guess at OS the memory allocated to shared pools + user storage (ST02) is also considered?

Regards,

Ameya

Regards,

Ameya

Edited by: Ameya Joshi on May 8, 2010 3:09 PM

[Former Member]

Hi Emeya,

In SAP, virtual memory is physical memory + swap space. The VM allocated in st02 is indeed the total usage of your virtual memory. You cannot make a distinguish here if real memory is being used, or swap space.

The amount of memory you see for your WP via top is shared memory. So this 7GB is being shared by all your work processes. Your work process is only using a small amount of memory for private usage.

Kind regards,

Mark

[Former Member]

> The amount of memory you see for your WP via top is shared memory. So this 7GB is being shared by all your work processes. Your work process is only using a small amount of memory for private usage.

HI Mark,

So the Virtual memory allocated to SAP (ST02->Storage) is the one that we see on the OS when we use top command?

Or is it some kind of parameter set at OS level so that so much shared memory can be allocated to SAP?

Regards,

Ameya

Edited by: Ameya Joshi on May 11, 2010 3:26 AM

[Former Member]

So the Virtual memory allocated to SAP (ST02->Storage) is the one that we see on the OS when we use top command?

Yes, this is more or less the case.. So you can have multiple processes in top which are showing the same amount of memory, but the main part of this is being shared by these processes.

Of course there can be a deviation in what you see, since you don't see the exact amount of private/fixed memory that is being used by the process.

Or is it some kind of parameter set at OS level so that so much shared memory can be allocated to SAP?

As far as I know, this is not (yet) possible. With resource managers you can use this on CPU usage, but for memory this is not the case.

Kind regards,

Mark

[Former Member]

"The amount of memory you see for your WP via top is shared memory"

it's not only shared memory, but also local memory, or shared library, shared code etc.

Don't know what OS you refer to, for exampl, if you use AIX, you can use svmon to inspect the memory allocation of a process (physical or swap)

In context of "shared memory", which is still virtual memory, you need look for the virtual memory management of your OS.

[Former Member]

Hi Mark,

Can you please clear these doubts as well

Size of extended memory ..........KB . Is this too allocated from Physical+Swap or only Physical or only Swap ?

parameter em/initial_size_MB i think only limits the total usage of extended memory by all wp , am i right?

If yes then this parameter can be increased till amount of physical or physical+swap?

Regards,

Ameya

[Former Member]

> Hi Mark,
> 
> Can you please clear these doubts as well
> 
> Size of extended memory ..........KB . Is this too allocated from Physical+Swap or only Physical or only Swap ?

extended memory is allocated within the address space of virtual memory, OS manage each page of the extended meory whether it should be allocated to physical memory or "swap", you'd think virtual memory is a layer on top of physical memory + swap, rather than "different type of memory"

> 
> parameter em/initial_size_MB i think only limits the total usage of extended memory by all wp , am i right?

parmeter for max extended memory is depending on WAS version (incl. OS version)

e.g. for Linux and windows it's em/max_size_MB

and also it's limited by OS (sap does have os dependent EM parameters) and em/blocksize_KB, check the note 835474 please.

> 
> If yes then this parameter can be increased till amount of physical or physical+swap?

see my comment above

Edited by: Denny Liao on May 13, 2010 2:37 PM