Automatic memory Management in 11g for SAP ECC6.5

[Former Member]

HI,

I have configured Automatic memory with the oracle parameter Memory_target and after that SAP performance degraded tremendously. IS SAP support automatic memory ?

Platform Scenario:

Sun Solaris 10 ( Spark Platform)

Oracle 11.2.0.2

SAP ECC6 EHP 5

Earlier I had:

SGA_max_size 8G

Shared_pool_size 3.8G

DB_cache_size 3.8G

Pga_aggregate_target 5G

db_block_size 8KB

granule size 16 MB

Then I changed the parameters

Memory_target=13GB ( SGA + pga_aggregate_target i.e. 8+5)

Shared_pool_size =0

DB_cache_size =0

Pga_aggregate_target =0

But with this the performance goes down tremendously and eventually I revert the changes. Do I need to change any other parameter also?

Pl guide.

Regards

Gurbir Singh

[fidel_vales · Accepted solution]

Hi,

as Biborka has mentioned, SAP does not recommend to set it.

there are several problems with the "automatic" oracle things With this parameter, Oracle will decide how much memory puts in each area, and some times it decides to decrease too much the data buffer to put it on the shared pool, causing a huge increase on disk reads (slower) or reduces too much the data buffer, causing ORA-4031. This means that you should set the minimum sizes of this areas. ...

Resuming, it is better that you already set the mentioned areas and do not "touch/set" the SGA_TARGET

[Former Member · Accepted solution]

Hi Biborka / Fidel

I Understand that SAP does not recommend Automatic. But we can define the parameters to set minimum value of the parameter thus buffers have minimum size and above that automatic adjust may happen.

Moreover Automatic memory work tremendously well with other Non SAP Application..

Anyways answer is helpful

Thanks

[fidel_vales · Accepted solution]

Hi,

In the FAQ mentioned by Biborka you can see the parameters that have to be set to minimum values (fb_cache_size, shared_pool_size). Unfortunatelly, Automatic Memory Managemente does not work "very" well with SAP system with load. I've seen thousands of memory "allocation" per minute, which does not make sense (take x bytes from here and put it there, take x from there and put it here) as it is a lot of overhead (and some bugs also)

Still I would not set it at all, IMHO it is better to have fixed values.

[Former Member]

Hello ,
in addition to Fidel Vales comments , i can add one point.
Even if you do not use Automatic Memory management in Oracle 11 ,
there is still new feature works = "Automatic Shared Pool Extensions" , this means
if system detects that shared_pool is not big enough  , and you are about to have ORA-04031 error ,
it will automatically extend this pool , without any SGA_TARGET or MEMORY_TARGET configuration. I have seen this many times in our systems , this works more predictable and more
in accurate way (at least we didn't have problem with this).
You can disable this feature as well --> MEMORY_IMM_MODE_WITHOUT_AUTOSGA = FALSE
(but again if it works well , do not disable it).

P.S.  why you need PGA=5GB in such memory-limited system , especially you have ECC as mentioned ?

Regards , Sergo.

[former_member207186]

Hi,

Basically it is not recommended to use memory_target, for more details about memory configuration in general please refer to SAP Note 789011 - "FAQ: Oracle memory areas"

Please also check SAP Note 1431798 - "Oracle 11.2.0: Database Parameter Settings" which contains the SAP's recommendations for the parameters.

Regards,
Bíborka