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Shared memory issues.

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David Diaz
Occasional Advisor

Shared memory issues.

Hi all,
I'm trying to run 5 instances of Sybase on a V class server with 10 processors and 8Gb of memory. I also have allocated 12Gb of swap space. Whenever I try to run any combo of instances that exceed 2.5Gb of shared (to Sybase) memory I get a "kistartup: could not create shared memory" error.
I have set the chatr command for the dataserver binary and ran the mlock command as well. Here are some kernel parms as well;

maxdsiz 2063597568
maxfiles 2048
maxfiles_lim 2048
maxswapchunks 6036
maxuprc 100
maxvgs 20
nfile (36*(NPROC+16+MAXUSERS)/10+32+2*(NPTY+NSTRPTY+NSTRTEL))
nproc (20+10*MAXUSERS)
nstrpty 60
shmmax 7784628224
shmmni 512
shmseg 512
swapmem_on 0
unlockable_mem 1024

My question is: It seems that Sybase has a memory usage limit of 2.5Gb. Is there a way around this? Maybe by installing several dataserver instances or somehow fooling the RDBMS into 'thinking' it's only using 2.5 when in reality it's using more by adjusting the kernel parms?
I know its a long shot but I'm a little desperate here.

Thanks in advance for your help.
At the end of the game the king and the pawn go in the same box
8 REPLIES
Michael Steele_2
Honored Contributor

Re: Shared memory issues.

Are you 64 bit O/S? I know this is a 64 bit v class server but did a 32 bit O/S accidently get installed?

# getconf KERNEL_BITS

############################################

Launch STM and excercise you're memory.

############################################

You need a 64 bit application for the higher shared memory limits. Surely SYBASE has a 64bit version.
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David Diaz
Occasional Advisor

Re: Shared memory issues.

OS is 64 bit.
Sybase is 32 bit. In fact I have the last of the Mohicans (11.9.2). We're going to the 64 bit version (12.5) sometime last quarter 2003 or first quarter 2004.
At the end of the game the king and the pawn go in the same box
James R. Ferguson
Acclaimed Contributor

Re: Shared memory issues.

Hi David:

You are doing about as well as you can with a 32-bit application. You need to move t the 64-bit database to even begin to utilize the memory you have. When you do, remember that the 'maxdsiz_64bit', 'maxtsiz_64bit' and 'maxtsiz_64bit' parameters apply. The unsuffixed variants are for 32-bit programs.

Regards!

...JRF...
Steven E. Protter
Exalted Contributor

Re: Shared memory issues.

Last time I did a performance review we were maxing out at 50 shared memory segments.

512 might be a little high.

Here is a potentially useful tuning doc.

http://www1.itrc.hp.com/service/cki/search.do?category=c0&docType=Security&docType=Patch&docType=EngineerNotes&docType=BugReports&docType=Hardware&docType=ReferenceMaterials&docType=ThirdParty&searchString=UPERFKBAN00000726&search.y=8&search.x=28&mode=id&admit=-682735245+1059683118940+28353475&searchCrit=allwords

Document id: UPERFKBAN00000726

SEP
Steven E Protter
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doug mielke
Respected Contributor

Re: Shared memory issues.

Is Sybase's structure different than Oracle's SGA?
On our 32 bit versions, we're limited to about the same amount, but only per instance. New instance, new SGA, another chunk of shared mem.
I'm wondering if this is system wide shared memory limit, or something else, like individual user space...
Tim Adamson_1
Honored Contributor
Solution

Re: Shared memory issues.

Hi,

Have you considered implementing each of the DB instances in a separate memory window?

It was introduced via a patch and requires a kernel parameter to be changed.

See /usr/share/doc/mem_wndws.txt for more info.

It may get you out of a jam.


Cheers!
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Harrison M Leal
Occasional Advisor

Re: Shared memory issues.

Hi David

I have this problem, when you use one aplication in 32 Bits, your shared memory have one limitation of 2.75 Gb. Read this white paper, I believe that this document anger to help you.

http://www.docs.hp.com/hpux/onlinedocs/os/memwn1_4.pdf

Harrison.
Harrison M Leal
David Diaz
Occasional Advisor

Re: Shared memory issues.

Thanks for all your help guys.
The Memory Windows information was exactly what I needed. Using them I was able to start all 5 instances of Sybase with the required memory usage.
Again, much gratitude is owed to all of you.

David.
At the end of the game the king and the pawn go in the same box