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From: joel garry on 17 Mar 2010 15:02
hp-ux 11.23 Itanium, Oracle 10.2.0.4

I ran Oracle's rda tool (rda.sh -T hcve what they call a database
health check, they robotically ask for it with support calls), and it
tells me semvmx is too small. I have it set to 32767 as the install
guide and Oracle doc 169706.1 says, but the tool thinks it should be
32768.

I'm a bit skeptical of the tool, since it also tells me I need some hp-
ux patches that the Oracle doc says are 10.1 specific, but anyways,
I'm trying to figure out whether the 32768 is really different from
32767 for when I give Oracle support grief for sending me on a wild
goose chase with a bad tool. I see values like that and I think,
hmmmm, sounds like an exponent of 2 boundary, so maybe it is
important. So the question is:

Is that an important difference, enough to bring down production for a
kernel rebuild? Is this the sort of thing that might double semaphore
or other dependent memory structure sizes in actual use as Oracle
decides a granular boundary is passed? Or is it just something
trivial?

jg
--
@home.com is bogus.
http://www.signonsandiego.com/news/2010/mar/14/even-gps-as-tool-to-fight-crime-has-limits/
From: Mladen Gogala on 17 Mar 2010 19:56
On Wed, 17 Mar 2010 12:02:47 -0700, joel garry wrote:


> Is that an important difference, enough to bring down production for a
> kernel rebuild? Is this the sort of thing that might double semaphore
> or other dependent memory structure sizes in actual use as Oracle
> decides a granular boundary is passed? Or is it just something trivial?

Joel, semaphores are integer variables. This parameter simply determines
the maximum possible value of any single semaphore. Semaphores are one OS
word in size, each. HP-UX on Itanic has 64 bit word size, so you're not
saving any memory by setting it to 32767. Document is below.

http://docs.hp.com/en/B2355-60105/semvmx.5.html

As for the question whether it is important enough to bring the
production system down, the answer is "dunno, how important it is to do
the installation"? I don't think it's that important, if any single
semaphore crosses the value of 32767, that means that there are 32766
other semaphore holders and you may be having slight problems with
concurrency. Semaphore operations function this way: each process that
acquires the semaphore in shared mode increases its value by 1. Process
that wants to acquire an exclusive control cannot do so while the value
is larger than 0. Having semaphore value 32767 means that there are 32767
processes holding the resource in shared mode. Can you realistically
expect to have 32k processes accessing the same resources on that system?
If the answer is "no", you're good.

You should ask yourself one question: do I feel lucky? And do I like the
users of that system? If the answer to the 2nd question is "no", then
bring it on, or rather, bring it down.




--
http://mgogala.freehostia.com
From: joel garry on 17 Mar 2010 20:44
On Mar 17, 4:56 pm, Mladen Gogala <gogala.mla...(a)gmail.com> wrote:
> On Wed, 17 Mar 2010 12:02:47 -0700, joel garry wrote:
> > Is that an important difference, enough to bring down production for a
> > kernel rebuild?  Is this the sort of thing that might double semaphore
> > or other dependent memory structure sizes in actual use as Oracle
> > decides a granular boundary is passed?  Or is it just something trivial?
>
> Joel, semaphores are integer variables. This parameter simply determines
> the maximum possible value of any single semaphore. Semaphores are one OS
> word in size, each. HP-UX on Itanic has 64 bit word size, so you're not
> saving any memory by setting it to 32767.  Document is below.
>
> http://docs.hp.com/en/B2355-60105/semvmx.5.html
>
> As for the question whether it is important enough to bring the
> production system down, the answer is "dunno, how important it is to do
> the installation"? I don't think it's that important, if any single
> semaphore crosses the value of 32767, that means that there are 32766
> other semaphore holders and you may be having slight problems with
> concurrency. Semaphore operations function this way: each process that
> acquires the semaphore in shared mode increases its value by 1. Process
> that wants to acquire an exclusive control cannot do so while the value
> is larger than 0. Having semaphore value 32767 means that there are 32767
> processes holding the resource in shared mode. Can you realistically
> expect to have 32k processes accessing the same resources on that system?
> If the answer is "no", you're good.
>
> You should ask yourself one question: do I feel lucky? And do I like the
> users of that system? If the answer to the 2nd question is "no", then
> bring it on, or rather, bring it down.
>
> --http://mgogala.freehos.com

Yeah, I figured it seemed trivial, but since rda complained, and I've
seen some other settings to 32768 on the net, I had to ask.
Especially since all the hp references like the one you cited say all
the semaphore tunables are interrelated, but never say exactly how.
In the past I've noticed different sources cite different formulae for
figuring various kernel parameters, I guess so sysadmins can wear
pointy hats with moons and stars.

jg
--
@home.com is bogus.
http://oumathclub.wordpress.com/2009/11/27/card-shuffling-will-blow-your-mind/
From: Mladen Gogala on 18 Mar 2010 11:19
On Wed, 17 Mar 2010 17:44:15 -0700, joel garry wrote:

> I guess so sysadmins can wear
> pointy hats with moons and stars.

I used to be a sysadmin but I don't like pointy hats. If I wear anything
on top of my head, it has "NY Yankees" logo on it. No pointy hats.



--
http://mgogala.byethost5.com
From: joel garry on 18 Mar 2010 12:59
On Mar 18, 8:19 am, Mladen Gogala <n...(a)email.here.invalid> wrote:
> On Wed, 17 Mar 2010 17:44:15 -0700, joel garry wrote:
> >  I guess so sysadmins can wear
> > pointy hats with moons and stars.
>
> I used to be a sysadmin but I don't like pointy hats. If I wear anything
> on top of my head, it has "NY Yankees" logo on it. No pointy hats.
>
> --http://mgogala.byethost5.com

I've been the default sysadmin at most of the places I've worked since
I went unix/oracle. At one time (like SunOS 1.2, Duplix, hp-ux 9,
slackware etc.), I actually made an effort to know something about
it. Nowadays I've dropped into sysadmin 2.0 mode. I do have a couple
of propeller hats, one of my kids borrowed one recently to go to a
costume party. One time I went to a Renaissance Faire in full wizard
outfit, I must have some pix somewheres...

jg
--
@home.com is bogus.
My .sig in the early '90s:
"See your System Administrator?" I *AM* the #%@!?& System
Administrator!
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