Re: Solaris 10 shmmax

...AFAIK, processes attaching to the ISM share the same virtual-to-physical address data structures related to the shared mem. segment avoiding duplication (compared to regular shared memory address translation) and saving considerable CPU time and kernel memory which translates to improved performance. But this is per shared memory segment. If more then one mem. segment is allocated to oracle according to this logic it may theoreticaly (or may not) cause some performance penalty since we have more than one virtual-to-physical address data structures. I have played with this long ago on Solaris 8 and could not see some significant performance differences.
maybe I am wrong :-)

BTW, does anyone knows if DISM segments on Solaris now support large-page MMU? Regards,
Goran

On 3/26/07, Hameed, Amir <Amir.Hameed_at_xerox.com> wrote:
>
> U are probably right Kevin that this feature should not be disabled
> unless there is an absolute reason not to use it. There was a paper written
> by Bob Sneed a while ago where he had stated that multiple shared memory
> segments can impact performance. Steve Adams has also quoted him on his
> site:
> http://www.ixora.com.au/q+a/0107/04120647.htm
>
> Bob's white paper:
> http://www.sun.com/blueprints/0101/SunOracle.pdf
>
> This may not be an issue anymore.
>
> ------------------------------
> *From:* Kevin Closson [mailto:kevinc_at_polyserve.com]
> *Sent:* Monday, March 26, 2007 1:22 PM
> *To:* Hameed, Amir; kevinc_at_polyserve.com; ax.mount_at_GMAIL.COM;
> oracle-l_at_freelists.org
> *Subject:* RE: Solaris 10 shmmax
>
>
>
> I would also like to understand this a little better. One of my friends is
> running 10.2.0.2 on Solaris9 and Sun 6900. His shmmax is set to 20G and
> has 64GB RAM on the server and this is the only instance running on that
> box. He is seeing multiple shared memory segments on the server. Oracle told
> him to disable _enable_NUMA_optimization parameter which is enabled by
> default.
>
>
>
> …why? Why turn off the ability for Oracle to exploit the hardware
> acrchitecture? Is the output of ipcs so disturbing due to multiple
> segements? That just sounds like concern over nothing.
>
>
>
>

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