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Setting EM/initial_size_MB

Former Member
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Dear Experts,

we have opened an incident message with SAP support regarding some performance issue on our system,

and the recommendation they gave us is that we modify the parameter : EM/initial_size_MB but they didn't recommend any value and said its customer specific.

my question is : what is the equation for setting this parameter correctly ?

we have 154 GB physical RAM 

and the parameter EM/initial_size_MB is set to : 59000

OS: IBMI v7.1

Kindly advise.

Many Thanks In advance.

Regards,

Ahmed Salam.

Accepted Solutions (1)

Accepted Solutions (1)

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Hi Ahmed,

please have a look at SAP Note 808607. If you are running with a kernel 7.2x or higher, we recommend that you set profile parameters ES/TABLE=SHM_SEGS along with as4/MAXSHR64 and maybe ES/SHM_BASE_ADDR (not needed for the 7.4x kernels). Especially on larger hardware, ES/TABLE=SHM_SEGS provides better performance than the default. If you set ES/TABLE=SHM_SEGS, em/initial_size_MB becomes meaningless.

Is there any reason to assume that em/initial_size_MB is critical for your overall system performance?

Kind regards,

Christian Bartels.

Former Member
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Dear Mr Bartels,

Many thanks that you took the time to reply to my question,

i was already checking this note while you replied but i cant understand you last question

> Is there any reason to assume that em/initial_size_MB is critical for your overall system performance?

also please note that we currently  running ECC 6 EHP 7 NW 7.4 with kernel 7.42 Unicode.

Again Many Thanks for your kind Support.

Regards,

Ahmed Salam.

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Dear Mr Salam,

when asking for a reason, I wanted to understand why SAP recommended increasing the parameter. Now that I know that you are running with the 7.42 kernel, I would highly recommend that you take a look at SAP Note 2098347. In this SAP Note, we have summarized all findings in relation to performance with the 7.4x kernels.

Among the recommendations, there is the suggestion to look at the new parameter "PHYS_MEMSIZE". It is used to calculate the value for em/initial_size_MB, and that value then is used to calculate further parameters, such as abap/buffersize. The whole new concept of memory parameters with the 7.4x kernel is documented in SAP Note 2085980.

Kind regards,

Christian Bartels.

Former Member
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Thanks All for your support,

we extended the parameter as per Note 2098347.

and its working fine now,

i will update this discussion if we face any other related issues

Regards,

Ahmed Salam

Answers (2)

Answers (2)

ManjunathBasapp
Explorer
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Hello Ahmed Salam

The parameter em/initial_size_MB is operating system-dependent in that it is restricted by the

address space of the work process.The amount of extended memory should be proportionate to the amount of physical memory

- For 32 bit architecture, the address space is < 4 GB (in some operating systems even smaller).

- For 64 bit architecture, the address space is < 1.8*1018 bytes.

For 32 bit architecture, SAP recommends using em/initial_size_MB <= 2GB, (and even less for

some operating systems). For detailed recommendations, see SAP Notes 97497 or 103747.

Note : SAP Note number will be different depending your SAP/OS/DB versions.

Good Luck.

Manjunath

christoph_ostrop
Active Contributor
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Former Member
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Dear Chris,

thanks for your recommendation,

in the above note i find : em/initial_size_MB = (min(512000, $(PHYS_MEMSIZE) * 0.7))

does this mean it can be set to : PHYS_MEMSIZE * 0.7 ?

which in our case is 154GB * 0.7 ?

Thanks for your time.

Regards,

Ahmed Salam.

christoph_ostrop
Active Contributor
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>

> we have 154 GB physical RAM 

> and the parameter EM/initial_size_MB is set to : 59000

>

you should leave "a little" RAM for DB2-for-i, and systemjobs, 

so your first mentioned value EM/initial_size_MB is set to : 59000 

seems to be a good value for that.

Christoph

Former Member
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But SAP support recommended to modify it