RE: shmall on Linux recommendation
- From: "Herring Dave - dherri" <Dave.Herring@xxxxxxxxxx>
- To: "Oracle L" <oracle-l@xxxxxxxxxxxxx>
- Date: Wed, 13 Jan 2010 11:51:19 -0600
A little more info that I've uncovered. The value of 25165824 for shmall comes
from a formula listing shmall should be (shmmax / hugepagesize). shmmax is set
to 51539607552 (so the largest shared memory segment can be 48 GB),
hugepagesize is 2048 KB, so they calculation others have done is 51539607552 /
2048 = 25165824.
My problems with this are that shmmax is listed in bytes while hugepagesize is
in KB, so if using that formula it should be 51539607552 / 2097152. Also, my
understanding is that shmall should always be listed in terms of the default
server page size. So if huge pages are used, it should match the total space
of your huge pages but in terms of 4 KB pages, which means really shmall should
be 12582912.
Is any of what I listed in the 2nd paragraph correct? Sorry if it seems I'm
over analyzing this but to request a particular value I feel I need to know
exactly why and how I'm coming with a value (and then fully documented the
method and reasons).
Thx.
Dave Herring | DBA, Acxiom Database Services
630-944-4762 office | 630-430-5988 cell | 630-944-4989 fax
1501 Opus Pl | Downers Grove, IL, 60515 | U.S.A. | www.acxiom.com
Service Desk: 888-243-4566
-----Original Message-----
From: Herring Dave - dherri
Sent: Tuesday, January 12, 2010 9:54 AM
To: Oracle L
Subject: shmall on Linux recommendation
Folks, I've inherited a 4-node RAC plus DG environment that has a rather
curious shmall setting that I'd appreciate your thoughts on. I've done my best
to understand it's current setting but those that made the decision are no
longer with the company and/or client.
The system is running 10.2.0.2 on RHEL 4. Like I said, it's a 4-node RAC, 64
GB RAM, with the same for a physical standby. Currently the SGA of each
instance is 17 GB.
The install guide gives a minimum value of 2097152 (8 GB) while the current
value is 25165824 (96 GB). To me it seems just a wee bit aggressive to be
setting the total shared memory to be RAM + swap! MOS doc 301830.1 gives the
recommendation of the SUM SGAs on the server, so in this case 4456448 (17 GB).
Sizing shmall to be the SUM of the SGAs on the server makes sense, but I'm
curious if anyone has experience that suggests otherwise? Also, can anyone
think of a good reason to set shmall to RAM + swap (other than "'cuz it's
there")?
Thx.
Dave Herring | DBA, Acxiom Database Services
630-944-4762 office | 630-430-5988 cell | 630-944-4989 fax
1501 Opus Pl | Downers Grove, IL, 60515 | U.S.A. | www.acxiom.com
Service Desk: 888-243-4566
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