Kernel parameters and swap space for SAP

[Wayne Green]

Just looking for some comparison information as this place is normally such a good source of information.

Any body running SAP 4.6B on HP-UX 11.00 64bit can post the shared memory, maxdsiz parameters used and the amount of swap configured.

I have just upgraded 4 K370 boxes from 10.20 to 11.00, cold install. 1 DB server and 3 app servers running SAP 4.6B. SAP recommended kernel parameter changes which were applied to all of them. They also recommended a huge amount of swap to be configured which we didn't have so its been limited to around twice memory. approx 3GB memory on all servers. All OK apart from one app server which reported a "shmget error insufficient space" trying to start SAP. The SAP profile has been tweaked by SAP basis guys so its all running but I'm looking for some recommendations for swap as they have found a post from SAP support which suggests that the maximum amount of shared memory that SAP can use is defined from the total amount of swap configured not shmax?

[harry d brown jr · Accepted solution]

Wayne,

Heres a thread:
http://forums.itrc.hp.com/cm/QuestionAnswer/1,,0x486e1cc6003bd6118fff0090279cd0f9,00.html

This is interesting also:
http://h40045.www4.hp.com/preinstall/rapid_it.html


live free or die
harry

[George_Dodds]

Wayne, did you work in Atherstone many moons ago?

Cheers

George

[Bill Hassell]

Is SAP running 32bit executables? If so, then shared memory is SEVERELY restricted, starting at just under 1000 megs, extendable to 1750 megs, but you may not be able to find the chunks requested by SAP because of fragmentation. While SAP is partially correct that maximum shared memory can be limited by swap space, that is a very incomplete answer.

Since the error referred to shared memory, the first thing to do is to download a copy of shminfo so you can see how badly fragmented shared memory (32bit) has become. Get a copy from:

ftp://contrib:9unsupp8@hprc.external.hp.com/sysadmin/programs/shminfo/

If SAP needs a segment that is 500 megs in size, but fragmentation has left 10 segments of 250 megs, SAP will fail. The requested segment must be contiguous. You have 2 choices:

1. Always start programs in a specific order after a reboot, and shut them down in a similar manner. Make sure all programs using shared memory are known and part of this sequence.

2. Use memory windows to provide unfragmented shared memory.

The 3 documents you need are found in /usr/share/doc:

mem_mgt.txt
mem_wndws.txt
proc_mgt.txt

(there are Postcript versions that are easier to read) If the mem_wndws.txt file is not there, you are not up to date on patches, perhaps a year behind.

The kernel parameters for shared memory, specifically shmmax, limits the maximum single shared memory segment but does not guarentee that it will be available. Note that 64bit processes do not have these limitations.

[Wayne Green]

Harry, thanks for the thread. Didn't spot that in the 100 I found. Answers the question, they seem to have got the same recommendations apart from maxdsiz_64bit has the shmax value and maxswapchunks is set to 2048 which is odd and correct me if I am wrong, limits addressable swap to 4GB. I'll check out the HP SAP site later.

George, indeed yes, another incarnation. Didn't you used to ride in from miles away on some knackered out motorbike? Hope you've graduated to something made in this century.

Bill, yes we are running 32bit SAP at the moment. To be upgraded shortly, one step at a time. That util will answer the question just put to me, thanks alot much appreciated.

[George_Dodds]

Well well, Mr Green.

I'm still commuting miles (a lot more!) but swapped using a knackered motorbike for knackered trains to get to London.

Drop me a mail on george_dodds@yahoo.com and let me know what you've been up to.

Cheers

George