Shared memory max

[Ken mooney_2]

I'm trying to help our sybase DBA's to allocate more memory to Sybase. The
server is a HP9000/K570 running Hp-UX 10.20 for the GEAC product
SmartStream,we currently have 4 GB of memory on the machine. I understand the
shmmax is 1GB, (SAM won't let me go beyond that).I have been told that I can
modify the /stand/system file to increase the shmmax then do a make kernel but
I'm not sure of the support issues from the Sybase and GEAC side if something
goes wrong doing an unsupported process. I have also found info on the Sybase
web page http://techinfo.sybase.com/css/techinfo.nsf/DocId/ID=20101
that says you can add these patches to increase memory. I have had no success
in trying to resolve this issue and my knowledge of shared memory segments is
real limited !!
Any input and assistance would be greatly appreciated.
THANKS !
Ken

[Neil Gast_1]

Even if you can increase shmmax beyond 1G via patch, I'm not so sure you would
want to. Instead, you should probably take a look at shmmni and shmseg, which
define max system-wide identifiers and max segments per process, respectively.
The default value for shmmni (200) is usually too low for database servers.

You can query your kernel parms with the sysdef command (10.20 & 11.x), or with
kmtune (11.x).

MrNeil

[Jason Luginbuhl_1]

Some info on increasing shmmax:
1) Increasing shmmax will only have an effect on those applications which are
compiled with SHMEM_MAGIC. Consult your application vendor to see if this is
the case. If not, the application will need to be relinked as a SHMEM_MAGIC
executable or else it will not be able to take advantage of shared memory
segments greater then 1 GB.

2) The limit of shmmax on 10.20 system is 1 GB until patches are installed.
These patches are PHSS_17903 and PHKL_16751 and any dependencies to these
patches. These patches have many dependencies. Be sure to resolve them before
installing.

3) Once the patches are installed, you shmmax value can be increases as high as
2.75 GB. The shmmax kernel parm in /stand/system is given in bytes. As such the
largest it could be would be (2.75 GB):
shmmax 2952790016

Hope this helps.