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@xxxxxxxxx> 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@xxxxxxxxxxxxx]
*Sent:* Monday, March 26, 2007 1:22 PM
*To:* Hameed, Amir; kevinc@xxxxxxxxxxxxx; ax.mount@xxxxxxxxx;
oracle-l@xxxxxxxxxxxxx
*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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