NW2004s Flat Memory Model and Windows 2003 SP2

[Rudi_Wiesmayr]

Hi!

Have a look at SAP Note 1002587 - Flat Memory Model on Windows

-> https://service.sap.com/sap/support/notes/1002587

This new performance opportunity of the (I think) NW2004s SPS 11 kernel sounds interesting for more throughput for the cost of more memory.

Is this interpretation correct?

Are there benchmarks showing the improvement?

And: Microsoft KB article 908929

--> http://support.microsoft.com/kb/908929/en-us

describes a problem when FlatMemory is used.

MS&SAP experts please: Does that mean that we should use the new FlatMemory ONLY after having installed Windows 2003 SP2?

And: Will there be a downport to the 6.40 kernel for Itanium?

Kind regards, Rudi

[Former Member · Accepted solution]

> This new performance opportunity of the (I think)

> NW2004s SPS 11 kernel sounds interesting for more

> throughput for the cost of more memory.

yes and now. After installation of KB929620 the performance the old map model is comparable to the new flat model as long as memory protection is turned on - and that is the only way flat model is supported on windows. Memory protection is stil very expensive.

> And: Microsoft KB article 908929

> --> http://support.microsoft.com/kb/908929/en-us

> describes a problem when FlatMemory is used.

>

> MS&SAP experts please: Does that mean that we should

> use the new FlatMemory ONLY after having installed

> Windows 2003 SP2?

no, you can also use it together with SP1 and the fix.

> And: Will there be a downport to the 6.40 kernel for

> Itanium?

no, currently there are no plans to downport to 640. well to be more precise... the flat model is already there, but only unprotected which is not supported by sap.

[Rudi_Wiesmayr · Accepted solution]

Thanks Simon.

So you recommend using flat model provided that

- the kernel patch is implemented

- KB929620 is installed as a precaution

- the machine has enough memory

On machines with plenty of memory and high workload I should see more memory consumption and hopefully less CPU per dialog step,

On machines which have little or no memory free I will see no benefit.Or even memory getting short and paging going up?

Kind regards, Rudi

[Former Member]

Trying to provide some more details:

the main difference between the view and flat model is, that in the view model the work process does only map those pages belonging to the ABAP user context it is currently processing into its working set. The pages will be unmapped at the end of processing of the request. The advantage of this model: minimum working sets, only those pages are mapped which belong to the currentl processed context, no additional memory protection needed. disadvantage: moderate pageoutes, without MMFix very high pageouts.

In the flat model all user contexts are mapped to all work processes all the time. no page is mapped/unmapped at any time during user context rollin or rollout actions. This seems to be a big benefit.

But you have to protect the memory pages of user contexts currently not under process in every work process against unintentionally, faulty access which may occure in case of wp crashes or other errors. advantages: no paging overhead, no map/unmap overhead. disadvantages: memory protection causes currently a very high cpu load.

concerning performance figures, following rule of thumb:

view model (with MMFix) compared to flat without memory protection:

cpu consumption: view is slightly more expensive than flat 1-2%. the difference is in the range of the messurement error.

paging: 64kB/sec pagewrites (view) 0 kB/sec (flat)

view model (with MMFix) compared to flat with memory protection:

cpu consumption: view model is only 50% of the cpu resources of the flat model!

paging: 64kB/sec pagewrites (view) 0 kB/sec (flat).

runing the flat model without memory protection is like driving a car without seatbelts in a race. You can only do it if the result of what is running needs not to be accurate and reliable.

you may now ask, why did SAP publish the configuration of the flat model.

Well, at a time when Microsoft was not yet able to deliver the memory management fix, we had preshure from projects where they where not able to use more than 10 % of there cpu resources because pageouts to pagefiles thwarts the overall performance of their system. In this situation the system performs a lot better, when having no pagesouts but 100% cpu consumption.

conclusion: the Flat model with memory protection is not supported. With memory protection there is a major disadvantage compared to the view model.

May be this will change with the upcoming windows longhorn version, but up to then: stay on the view model with the MMFix!

regards

Peter