Question Re: used memory WP in Technology Q&A

used memory WP

Naor_Shalom — Tue, 20 Oct 2015 14:47:37 GMT

HI,

I have a few questions regarding memory management in SAP system.

I read about it a lot butI still confused

My question is:

1. How I know how much memory all the WPs is used? (How much memory all the WPtakesfrom the OS)

2. How I know how much memory all the DIA's is used? (How much memory all the DIAtakesfrom the OS)

Idontwantseperateit to extend memory roll areaetc, I want to know percentage of memory all the WP takes from the OS.

I asked it becauseineed to increase the number of DIA in the APO system, but before the change I want to know how much memory the WP and the DIA used now, I want to avoid frommemory problemin the OS afteriincrease the number of DIA.

My server is always around 80% memory used, but I limit the memory used bySAP systemwith the parameter PHYS_MEMSIZE, and Idontthink the SAP takes all the PHYS_MEMSIZE parameter value.

And it'stakeme to the 3 question:

3.howI know how much memory the SAP system takes fromOS? I limit the memory used by SAP with PHYS_MEMSIZE, but I want to know exactly how much memory the SAP takes and if he used all the valueigive in the PHYS_MEMSIZE.

Maybe Idontneed to increase memory in the server just to increase the number of DIA

Thanks for your help my freinds

Naor

Re: used memory WP

Isaias_SAP — Tue, 20 Oct 2015 16:14:49 GMT

Hello Naor,

Each work proess will use some memory just to "exist" in the system (something around 100MB - 200MB, depending on the SAP kernel release in use).

Besides that, I believe you can use the sappfpar output to have an idea of how much memory SAP will use.

You can execute this tool at operating system level (notice that the "pf=..." argument has to be adjusted):

sappfpar check pf=/usr/sap/SID/SYS/profile/instance_profile

Keep in mind that sappfpar will not account the "heap memory" (parameter "abap/heap_area_total").

The heap memory is allocated and freed dynamically, as the system needs.

Regards,

Isaías

Re: used memory WP

yakcinar — Tue, 20 Oct 2015 17:45:47 GMT

Hello Naor,

As you may know ST02 Tx is the place where you need to check about memory usage in SAP instance.

Let me try to explain the topic with some parameters and formulas;

Here is the total memory usage for an SAP System including DB. Maximum usage of the memory can be found using this formula.

Total Memory Used by SAP & DB =

DB memory (rule of thumb 1/3 of Host memory) +

(Total Alloc KB in ST02 – Total Freesp. KB in ST02) +

Roll Area Max Use in ST02 second table +

Page Area Max Use in ST02 second table +

Extended Mem Max Use in ST02 second table +

Heap Memory Max Use in ST02 second table

You cannot calculate the max usage of memory using dia or non-dia wps count because all wps use a shared extended memory. There are parameters to limit the usages of this extended memory for each wp like ztta/roll_extension. You can check the usage and allocation of these parameters in ST02 transaction.

SAP keeps local memory of each wps very small in order all wps to use shared memory. For performance and usage reasons.

One more thing that needs care is;

Under normal conditions heap area usage is not accepted. If a wp is using heap memory it means it is in PRIV mode. And using unshared memory area. This is not wanted. This is limited with abap/heap_area_total parameter.

You can check below link for a presentation.

SAP Memory Management

Regards,

Yuksel AKCINAR

Re: used memory WP

Naor_Shalom — Wed, 21 Oct 2015 06:51:35 GMT

HI.

First Iwant to thanks for your help

So if I understandcorrect thereis no way to know what is exactly the used memory of the WP\DIA?

And what about the all SAP memory?

I ask you another question.

Let's say you need to increase DIA in your sap system. whatdo you check before you do it, from the memory side, to be sure you will not have memory issue.

Thanks Naor

Re: used memory WP

Naor_Shalom — Wed, 21 Oct 2015 06:55:01 GMT

Dear Yuksel

You can help with this:

DB memory (rule of thumb 1/3 of Host memory) + ST04?

(Total Alloc KB in ST02 – Total Freesp. KB in ST02) + where ifind this in ST02? thefirst table?

Re: used memory WP

yakcinar — Wed, 21 Oct 2015 07:21:32 GMT

Hello Naor,

Answers are below

So if I understandcorrect thereis no way to know what is exactly the used memory of the WP\DIA?

- Yes, at startup wps allocates some memory but it is neglectable when wp is in wait status. Whenever a user runs an activity on that wp it allocates memory from extended memory with a limit roll_extension. When it finishes it uses heap memory to a limit also.

You can chek below links

Memory Management: Basic Concepts - Architecture of the VM Container - SAP Library

Virtual Address Space of a Work Process - SAP Memory Management (BC-CST-MM) - SAP Library

SAP Memory Management (BC-CST-MM) - SAP Library

Allocating Memory for User Contexts (UNIX) - SAP Memory Management (BC-CST-MM) - SAP Library

And what about the all SAP memory?

Use the formula to find total SAP memory usage. I add screenshot of ST02.

I ask you another question.

Let's say you need to increase DIA in your sap system. whatdo you check before you do it, from the memory side, to be sure you will not have memory issue.

In this situation if you donot change memory parameters total SAP memory usage will not change. Or change is neglactable. Very small. All wps will use extended memory. If it is exhausted you will get memory dumps. And some programs will use HEAP area till limit also.

Increase #of wps and monitor your system from ST02 and ST22. Check PHSY_MEMSIZE parameter if you increased host memory. On windows this parameter is automatically set by SAP so you can check zero memory management note for windows.

Regards,

Yuksel AKCINAR

Re: used memory WP

Naor_Shalom — Wed, 21 Oct 2015 07:38:51 GMT

Dear Yuksel

So if I want to know all the sap memory

I calculate this formula

max total allocated + max total freespace + max uses = all sap memory ?

Thanks

naor

Re: used memory WP

yakcinar — Wed, 21 Oct 2015 07:47:34 GMT

Hello Naor,

Use this formula. There are minuses as well.

Total Memory Used by SAP & DB =

DB memory (rule of thumb 1/3 of Host memory) +

(Total Alloc KB in ST02 – Total Freesp. KB in ST02) +

Roll Area Max Use in ST02 second table +

Page Area Max Use in ST02 second table +

Extended Mem Max Use in ST02 second table +

Heap Memory Max Use in ST02 second table

Can you send your ST02 as screenshot and as text also. And current memory parameters. I will try to calculate it for you.

Regards,

Yuksel AKCINAR

Re: used memory WP

Naor_Shalom — Wed, 21 Oct 2015 08:14:29 GMT

Buffer HitRatio % Alloc. KB Freesp. K

Nametab (NTAB)

Table definition 99.96 25,211 11,881

Field definition 100.00 125,861 73,304

Short NTAB 100.00 6,321 3,222

Initial records 98.74 37,345 29,911

program 99.92 1,800,000 686,254

CUA 99.97 13,000 1,179

Screen 99.98 19,532 1,757

Calendar 100.00 488 316

OTR 100.00 4,096 3,327

Tables

Generic Key 100.00 200,000 27,451

Single record 97.36 40,000 10,857

Export/import 98.46 75,000 10,907

Exp./ Imp. SHM 99.57 4,096 2,178

SAP Memory Curr.Use % CurUse[KB] MaxUse[KB]

Roll area 1.21 3,175 11,784

Page area 0.45 1,183 262,136

Extended memory 2.72 913,408 6,385,664

Heap memory 0 2,244,228

PHYS_MEMSIZE 25600

total memory - 32 GB

Oracle - 17 GB

Thanks

naor

Re: used memory WP

yakcinar — Wed, 21 Oct 2015 08:28:40 GMT

Hello Naor,

First of all your DB has more than 1/3 of host memory rule value. As I said rule of thumb it should be about 10-12 GB. Check Oracle memory usages also. Does Oracle use all allocated memory?

PHYS_MEMSIZE + DB MEM SIZE = 25 + 17 = 42 GB. Your system must swap at least 10 GB from these values.

What about the swap size of your system? Is it 2-3 times of your host memory?

I will do calculations later. No time now. And reply later.

Regards,

Yuksel AKCINAR

Re: used memory WP

Naor_Shalom — Wed, 21 Oct 2015 08:31:00 GMT

46 GB SWAP

Thanks

Naor

Re: used memory WP

Reagan — Wed, 21 Oct 2015 13:21:32 GMT

If you increase the number of work processes for an instance then you should make sure there is enough memory on the machine and if not you should increase memory (RAM). Like Isaias said every process will need memory from the OS to exist. It is not just for SAP work processes, any process/activity running on a machine will need memory. As you have an Oracle database when you increase work process you should increase the processes and sessions parameter. This means you should consider memory for Oracle processes. The recommendation from SAP is to consider 250 MB per work process but I would say 250 MB is quite a lot and maybe SAP is suggesting it as a defensive strategy. I normally check the ST02 detailed analysis for information about memory used by each work process. The parameter PHYS_MEMSIZE will limit the memory to be used by the SAP system.