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How to calculate PHYS_MEMSIZE ??

Former Member
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Hi ,

I have a little question and i couldn't find the solution.

Imagine a server with for example 4 Go RAM.

How to calculate PHYS_MEMSIZE :

PHYS_MEMSIZE= RAM - (OS RAM need + DB RAM need) ??

Or only DB :

PHYS_MEMSIZE= RAM - DB RAM need

Thanks in advance,

Regards,

Patrick

Accepted Solutions (0)

Answers (3)

Answers (3)

Former Member
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Hi,

Thanks for all your answers. For std implementation in 64bit, my customer will manage his system himself and SAP is new for him.

I keep ZAMM system because it will be more "friendly" for the beginning.

If I understand there is no difference between an application server and a central instance ??

AS => PHYS_MEMSIZE = 100%

OK

CI => PHYS_MEMSIZE = 100%

No memory will be used on the database ?

For windows server :

PHYS_MEMSIZE is calculated like that :

PHYS_MEMSIZE= 60% (RAM - OS RAM need) and DB allocated RAM is 40% (RAM - OS RAM need) .

Percentage depend on DB software : between 60% and 70% for PHY_MEMSIZE

How Linux could be different ?

One solution is PHYS_MEMSIZE 100% doesn't mean all memory allocated to sap directly but simply on request.

In case of bottleneck in memory consumption, it will change nothing that missing memory was "just declared" as allocated to SAP .

Example of snapshot of the situation:

PHYS_MEMSIZE = 100 %

In case of a high demand in memory, I will find for example :

OS allocated memory = 5 % (for example, in fact it would be as much as needed)

DB allocated memory = 35 %

SAP allocated memory = 60%

And if PHYS_MEMSIZE= 60%

In case of a high demand in memory, I find for example :

OS allocated memory = 5 % (for example, in fact it would be as much as needed)

DB allocated memory = 35 % ( or perhaps 30% !!! )

SAP allocated memory = 60%

Is it for this reason that you suggest to put PHYS_MEMSIZE= 100% ??

bests regards,

Patrick

former_member204746
Active Contributor
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if CI and DB is on the same server, give out 70% of memory to SAP and 30% to DB.

so, you have 8GB, you give 1GB to OS, set PHYS_MEMSIZE 5GB for SAP and 2GB to Oracle.

if your CI is standalone or you have standalone APPS, then DO NOT set PHYS_MEMSIZE.

Former Member
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I recommend always to leave PHYS_MEMSIZE=100% if there is only a single SAP application server instance - DI or CI - running on this system, independent whether there is a database running or not. PHYS_MEMSIZE only tells the SAP system how much SAP Extended Memory (TMPFS - under /dev/shm) it could use at maximum (em/max_size_MB).

So PHYS_MEMSIZE is mostly irrelevant for sizing matters, it doesn't force the SAP system to use only the specified amount of RAM...

Regarding ZAMM - on 64-bit systems the memory management handling with es/implementation=std is most probably less complex than "map", if you are familiar to other SAP on Unix systems.

Regards,

Alexander.

Former Member
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Hi alexander,

Thanks for your helpfull answers.

Just one more question please :

TMPFS is calculated like that on 32bit systems :

TMPFS= 75% (RAM+SWAP)

But in 32bits systems SWAP is very small (2*RAM )

In 64bit systems :

I have 16 Go RAM and 32 Go Swap , how to calculate :

TMPSFS = 75% *48 =36 Go ??

Thanks,

Patrick

Former Member
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I have just seen that TMPFS must never be more than 2*Physical Memory.

Then ... TMPFS = 32Go MAX ?

regards

Patrick

Former Member
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If you have only 1 application server you can delete the parameter and sap automatically uses the meme it needs

Former Member
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Hi Patrick,

as PHYS_MEMSIZE more or less only configures the parameters em/initial_size_MB and em/max_size_MB, I'd always recommend to keep it at its default "100%" - maybe unless you configure multiple SAP ABAP Application Servers on the server.

Please keep in mind: PHYS_MEMSIZE does not limit the application server to use only the specified amount of RAM (see note <a href="https://service.sap.com/sap/support/notes/386605">386605</a> for more details).

In general, when using 64-Bit hardware, please consider switching to es/implementation=std (note <a href="https://service.sap.com/sap/support/notes/941735">941735</a>) instead of using map and the PHYS_MEMSIZE mechanism.

Regards,

Alexander.