SHMMAX

[Unix Admin_2]

Environment: N class machine with 4G of physical memory and 2x36G internal disks, swap is 4G, OS HP-UX 11.0, Sybase Server.

DBA asked to have shmmax as 3.5G
HP docs say: max value for shmmax is 1792M. This limit can be disable by setting the shmmax to 1fffffff and OS imposes its own hard limit for share memory.

I did not use this before, so I would like to know what is this "own hard limit"? Is it 4G or less?
Is OS going to run ok? Is HP supporting that?
Is any impact in performance?

Your opinion will be appreciate.
Thank you.

[Patrick Wallek]

You should have no problem setting shmmax to 3.5G on your system. Have a look at this web page:

http://docs.hp.com/hpux/onlinedocs/os/KCparam.ShMmax.html

It shows the max value for HP-UX 11.0 64 bit to be 1 TERABYTE! It also says that the value can not exceed the max. available swap space. Since you've got 4G of swap, the 3.5G shmmax should work fine.

[Helen French]

Hi,

The Max. value of shmmax in 64bit systems is 1 Tbyte !

See this:

http://www.docs.hp.com/cgi-bin/otsearch/getfile?id=/hpux/onlinedocs/os/KCparam.ShMmax.html&searchterms=SHMMAX&queryid=20020110-192344

HTH,
Shiju

[Sanjay_6]

hi,

The limit is 4TB on a 64 bit OS. Take a look at the thread below,

http://us-support.external.hp.com/cki/bin/doc.pl/sid=b2f5300d13b4d5d909/screen=ckiDisplayDocument?docId=200000047272187

Hope this helps.

Regds

[Helen French · Accepted solution]

Hi,

You may not have performance issues by doing this. Check these links:

http://us-support.external.hp.com/cki/bin/doc.pl/sid=00d21f7b0f8df52c30/screen=ckiDisplayDocument?docId=200000047272187


http://us-support.external.hp.com/cki/bin/doc.pl/sid=00d21f7b0f8df52c30/screen=ckiDisplayDocument?docId=200000032087693

HTH,
Shiju

[Unix Admin_2]

Thank you to all. I will assign points later, so far I???m a bit confused. The link indicated by Shiju Wilson said: ???By setting shmmax to the maximum allowed value (0x10000000000), you risk having a process erroneously try to allocate a huge segment and consume all available swap space, only to be denied the request.Another possible problem is that legitimate requests for swap could be denied while the shmget() was processed. This problem is similar to setting maxuprc to a fraction of nproc. If an application erroneously and continuously forks, it should not be allowed to consume the all process table slots.??? ?????

More than that: I went and changed shmmax to 0xA0000000 ~ 2684354560 (aprox 2.6G) and the DBA said he can allocate to Sybase just 1.6G.

kmtune report shmmax=0xA0000000. ??????

[Ruediger Noack]

I think for 3.5GB shared memory 4GB physical memory is not much! You have to increase it.
Additional you should increase the swap to minimum 2 times of physical memory.

Ruediger

[Steven Gillard_2]

32bit applications are still constrained to the ~1.6Gig limit even if shmmax is set higher. If you want to use >1.6Gig you will need to install a 64bit version of Sybase.

Regards,
Steve

[Unix Admin_2]

First of all, thank you to all of you. Patrick and Ruediger, can you, please reply one more time to this post I owe you some points.

Sorry for my ignorance. Can anyone tell me how to check if Sybase???s version if is 32 or 64 bits?
Runing a strings command on dataserver and grep for Adaptive
#strings dataserver | grep Adaptive
come back with
???Adaptive Server Enterprise/11.9.2.5/1227/P/SWR 9619 ROLLUP/HP9000-735/HP-UX 10.2/FBO Tue Jun12 08:50:09 2001???
guess HP-UX 10.2 is coming from HP-UX 10.20 that is 32 bits but not sure.

1.Is any other way to check Sybase version?
2.Can you please, re-confirm what is the max share memory that Sybase can use it?

Many thanks,
A.

[Patrick Wallek]

It appears as if your version of Sybase is 32-bit since it mentions 10.20 in your strings output.

To verify, you'd have to find the install media. If it doesn't specify that it is 64-bit, then it probably isn't.

A 32-bit application can typically only handle slightly less than 1.75 GB of shared memory.

Good luck.