Re: shmall on Linux recommendation
- From: Surachart Opun <surachart@xxxxxxxxx>
- To: Dave.Herring@xxxxxxxxxx
- Date: Thu, 14 Jan 2010 01:32:11 +0700
From RedHAT
if you:
# grep Hugepagesize /proc/meminfo
Hugepagesize: 2048 kB
Yes, You see KB, But In formula:
# grep Hugepagesize /proc/meminfo|awk '{print $2}'
2048
So, huge (variable) = 2048
You should be 51539607552 / 2048 = ??? (shmall)
That is redhat idea, However you should look at less shmall value should be,
If you set less than that ... you can not start database
Example: You plan use sga_target=51539607552 and PAGE_SIZE=4096 ... shmall
>= 12582912
I think you should look at Oracle recommend.
MEM=$(free|grep Mem|awk '{print$2}')
PAGE_SIZE=$(getconf PAGE_SIZE)
shmall=$MEM/$PAGE_SIZE
Surachart Opun
http://surachartopun.com
On Thu, Jan 14, 2010 at 12:51 AM, Herring Dave - dherri <
Dave.Herring@xxxxxxxxxx> wrote:
> 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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