Memory allocation question on HP-UX

[former_member236859]

Hi,

I am not familiar with HP-UX and am confusing of the memory management on it.

1. SAP parameter 'em/initial_size_MB' specified the extended memory size. Is this all allocated (or blocked by HP-UX) after SAP system start up?

(Blocked by HP-UX which I mean it seems not like other OS (Windows), which support dynamic memory allocation...)

2. Oracle parameter 'sga_max_size' specified the maximum SGA size. Is this all allocated (or blocked by HP-UX) after Oracle database start up?

As an example, a server has 12GB physical memory and swap space is 20GB.

Profiles are:

em/initial_size_MB=5120MB -> 5GB

SAP buffers are allocated about 1.6GB

sga_max_size=5153960756 -> 4.8GB

pga_aggregate_target=1288490188 -> 1.2GB

i. Does this configuation mean that after system start up (SAP and Oracle database), totally 51.64.8+1.2=12.6GB memory should be allocated?

ii. Does it mean the physical memory is insufficient to afford this configuration?

Thanks a lot.

Regards,

Alex

[former_member314436]

Hi,

From the OS perspective it is vital here to distiguish between "virtual memory" and "physical memory".

The majority of all the memory usages mentioned in this thread (Oracle SGA, SAP shared memory etc.) are all allocated from virtual memory. The resulting physical memory usage then depends on how many of these "virtual memory" pages are actually in use (commonly known as the "working set").

There are then three things to consider:

1. For things to run/start at all you need enough "virtual memory" available for for SAP, DB, OS etc.

This can be easily checked on HP-UX with the "swapinfo -tam" command. Checke the last line called "totals". That last line is you total virtual memory, check the percentage used.

2. For things to run well (i.e. achieve good performance) you need enough "physical memory" to make sure your system is not forced into lots of paging. You can check paging activity with HP-UX tools like glance, vmstat etc.

3. Dont forget, SAP and the DB are not the only memory consumers. There is the OS iteself and filesystems caches, which may also be significant.

See SAP Note 1112627 for an explanation of HP-UX swap recommendations and some hints on analyzing memory usage on HP-UX systems.

Best Regards

Lee

[former_member189546]

Hello,

Please check

425207 "SAP memory management, current parameter ranges",

em/initial_size_MB is total memory for all sap processes not set

aside at startup

regards,

John Feely

[Former Member]

Hi , many questions but not answers ..... )

SAP parameter 'em/initial_size_MB' specified the extended memory size. Is this all allocated (or blocked by HP-UX) after SAP system start up?

No , after startup not all of this memory are allocated , but after some time working this will be allocated .

As an example, a server has 12GB physical memory and swap space is 20GB.

12Gb are not enougth for this configuration ... You need for HEAP memore some space also ...

Try to check in ST02 --> detailed --> Storage (not included Oracle memory).

Regards.

[former_member236859]

No , after startup not all of this memory are allocated , but after some time working this will be allocated. 

Thanks for the reply but I am not sure about this part.

Do you mean that allocating the memory need some time as system need to get 'hot'?

If I observe around 700MB extended memory consumption (of course sometimes heap is also being used), does all 5120MB extended memory will be allocated normally, or just 700MB is allocated at all?

Regards,

Alex

[Former Member]

Thanks for the reply but I am not sure about this part.

If you not sure ,try to check on live system what is the problem?

If I observe around 700MB extended memory consumption (of course sometimes heap is also being used), does all 5120MB extended memory will be allocated normally, or just 700MB is allocated at all?

I'm recheck now and if you add for extendent memory 5120MB all of whis will be allocated as i'm say before (but not directly after SAP is starting) ... For example in one of our HP-UX systems (64 GB main memory) currently are used for extended mem 2,5 Gb but from OS memory are allocated all 30 GB ....

Regards