Re: Oracle's max shmseg size on HP-UX

Brenda Muller wrote:
>
> Hi,
>
> I have gotten conflicting reports on the maximum amount of shared
> memory that Oracle 7.3 can use on HP-UX 10.20. I know the
> following:
>
> - HP-UX will not allow a single shmseg larger than ~1G
> - HP-UX will not allow a single process to grab more than 2 shmsegs
> - Oracle will grab one contiguous segment up to ~1G
> - Oracle will grab two segments if each one < ~500M
> - Oracle will fail if trying to grab two segments larger than ~500M.
> This doesn't mean that both were larger than 500M - one could be
> 520M and the other 200M and it will still fail.
> - HP-UX will allow a single process to grab two shared memory segments
> up to a total of 1.75G - each can be up to ~875M.
>
> We have tested the above points and they are facts.
>
> Oracle support has told us that Oracle can never take more than
> 1G for an instance. It's unclear whether they mean Oracle in general
> or Oracle on HP. I was (and am) under the impression that the max shm
> size for Oracle is 2G. But the guy didn't seem overly impressive in
> his knowledge, and he was difficult to deal with.
>
> We have a *huge* OLTP environment where we are trying to get our
> data buffer block area as large as possible. Does anyone know of
> a way to get around the above limitations?
>
> TIA,
>
> Brenda Muller
>
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First of all, what did your Oracle7 7.3 for HP-UX 10.x Installation and Configuration Guide specify for shared memory and semaphore settings? That information comes from development and the porting groups, the folks whom are responsible for determining that information.

I believe the 2GB/2 segment SGA cap is HP-specific, as all HP 9000 platforms look alike to Oracle, from G30's to T520's.

Also keep in mind that these are 32-bit processors, which will limit the size of a single address space. The DEC Alpha's, a 64-bit architecture, doesn't have this 2GB SGA limit.

-- 
Rich Woods
Technical Field Support Specialist, Oracle Corporation, USA
The above statements and opinions are my own and do not
necessarily represent those of Oracle Corporation.