maximum of shared memory

[Simon Jespersen]

Hi!
Is there a limition on shared memory shmmax
ive had learn that the maximum amount is approx 1,75 gb for the shmmax kernel parm. I would like to have that comfirmed or denied as i have a problem with an applikation and my vendor fist told me to increase the shmmax to 4gb and the shmmni from 1024 to 2048. After that the amount of crashes increased.

[Steven E. Protter · Accepted solution]

Shalom Simon,

shmmax maximum usable value is 25% of memory.

HP-UX defines memory as RAM plus swap.

Any figure higher than that will be ignored by the OS.

Example

6 GB memory with 6 GB swap.

12 GB memory by HP-UX rules

shmmax is 4 GB.

You can set it higher but the OS will ignore it. Certain oracle products require that shmmax be set to RAM total. This is oracle bs, the OS ignores it just like it would for any other reason.

SEP

[A. Clay Stephenson]

It depends upon whether or not this is a 32-bit or 64-bit version of the OS. For 64-bit HP-UX, shmmax can be much, much larger (in the TB range). If 32-bit code is compiled/lined as SHMEM_MAGIC then upto 2.75GB of shared memory can be used.

You should really look into memory windows because that way each group of related 32-bit processes gets their own 4GB address space.

http://docs.hp.com/en/5187-0172/ch10s05.html

[Simon Jespersen]

Thank you very much for yor useful anwsers. It did the trick for me, and im learning new stuff about shared memory.

[Arunvijai_4]

Hello Simon,

You can read this thread for more information and good materials,

http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=995788

-Arun