extend memory em/initial_size_MB to 20GB

[Former Member]

Dear All,

Our current configuration is

SAP BW 7.0 sp27,

Oracle 11.2.0.2.0

AIX 6.1

64 GB memory

8 * 2 CPU

Our extended memory setting is

em/initial_size_MB = 8192

Now SAP Expert recommand us extend memory em/initial_size_MB to 20GB, then

how much the memory configuration in OS level has to be enlarged before change extended memory in application level ?

Thank you,

Hong

[Former Member]

All,

Could you please tell me the what's the relationship between 'em/initial_size_MB' and 'RAM' ?

if I need extend 'em/initial_size_MB' from 8G to 20G, then how much should I enlarge the 'RAM' ?

THANKS,

Hong

[former_member182657]

Hi Hong,

Please follow SAP Notes  386605 - SAP Memory Management for Linux (32-bit)

and  922352 - Warning: em/initial_size_MB is bigger than em/max_size_MB

Hope this will help you.

Regards,

Gaurav

[divyanshu_srivastava3]

Hi Hong,

RAM + Swap = total memory for sap.

Now, user context goes 1st in roll 1st area, then extended, then remaining roll and then heap.

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

The below section comes from there.

SAP Roll Area	Sequential memory allocation to several work processes usin g a relatively slow copying process
SAP Extended Memory	Sequential memory allocation to several work processes using a fast allocation process Uses swap space
Private memory	Allocation to a local work process, as required for the running user context in the process Uses swap spape

Now it, for RAM means for a fixed swap reduces paging. But a balance is recommended.

Divyanshu

[alwina_enns]

Hello Hong,

the initial amount  'em/initial_size_MB' of extended memory will be allocated first, and it will be extended if needed until EM/TOTAL_SIZE_MB is reached. What is the value for EM/TOTAL_SIZE_MB in the affected system? It will not make much sense to increase only em/initial_size_MB, the maximum amount of extended memory is restricted by EM/TOTAL_SIZE_MB.

Reg. RAM - an estimation is

RAM+swap = heap + extended memory

regards,
Alwina

[Former Member]

Hi Alwina,

Below is from SAP expert recomandation:

Parameters	Description	Current Value	Recommendation
em/global_area_MB	Size of SAP Ext. Global Memory	250	256
abap/heap_area_dia	Heap memory limit for dialog workprocess	1000000000	2000000000
abap/heap_area_nondia	Heap memory limit for non-dialog workprocesses	1000000000	2000000000
ztta/short_area	Size of short-term memory	3200000	4000000
EM/TOTAL_SIZE_MB	AIX: Total Size of EM	6144	60664

we checked from OS that the memory used is alway in 80%, so we want to increase the phisical memory, but I don't know how much need to increase.

Could you pls give some advice ?

Tks,

Hong.

[alwina_enns]

Hello Hong,

thanks for the info. And which value is set for abap/heap_area_total? Could you please check also new ST06 (depending on release it could be ST06, ST06N or OS07N), what is displayed for "Configured swap size" and "Maximum swap size" in the snapshot data for "Memory"? What else is running on the same server - database or another instance?

Regards,
Alwina

[divyanshu_srivastava3]

Hi Hong,

Standard implementation of extended memory on AIX is using ES/TABLE=SHM_SEGS.

However,to avoid fragmentation use es/freelist_compactor=1

Check kernel patches for more info.

Divyanshu

[alwina_enns]

Hello Hong,

please have a look at this section in the note "1972803 - SAP on AIX: Recommendations":

"

4. AIX memory and paging-space

4a) Memory parameters

For AIX 6.1 and 7.1 usually the defaults are fine. For a detailed discussion
about the virtual-memory-manager behaviour and related 'vmo' parameters see Note
973227."

Which memory implementation is active in the system? If ES/TABLE = SHM_SEGS is configured, then the parameter em/initial_size_MB is not required to be set, EM/TOTAL_SIZE_MB should be used.

regards,
Alwina

[former_member182657]

Hi Hong,

Kindly follow SAP Note 103747 and refer recommendations under part 3a) Roll Buffer and Extended Memory

Regards,

Gaurav