Re: SHMMAX seems entirely broken in OS X 10.4.2

Has anyone been able to set kern.sysv.shmmax above 4MB at all in latest
OS X? I just spent a while trying what seemed every possible
permutation of setting up /etc/sysctl.conf and editing /etc/rc directly,
and it just fails (symptom: sysctl shows shmmax as -1, and Postgres
cannot start).

Grrr. Apple's been pretty lame about this from day one, but at least
it's been possible to do it one way or another.

(Curiously, it seems you can now change shmall after bootup in 10.4.2,
but that's not much help when you can't change shmmax.)

regards, tom lane

Tom,

On 8/29/05 5:18 PM, "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Has anyone been able to set kern.sysv.shmmax above 4MB at all in latest
> OS X? I just spent a while trying what seemed every possible
> permutation of setting up /etc/sysctl.conf and editing /etc/rc directly,
> and it just fails (symptom: sysctl shows shmmax as -1, and Postgres
> cannot start).
>
> Grrr. Apple's been pretty lame about this from day one, but at least
> it's been possible to do it one way or another.
>
> (Curiously, it seems you can now change shmall after bootup in 10.4.2,
> but that's not much help when you can't change shmmax.)

Yes - it's very strange, I've had the same experience though I finally found
that setting SHMMAX and SHMALL to the same values, namely 268435456, seems
to work out fine.

I don't have a hypothesis as to why that value works though. I suspect that
equal values of all sizes would work, though I stopped trying when I found
this pair and it worked on multiple machines.

- Luke

Tom Lane wrote:

>Has anyone been able to set kern.sysv.shmmax above 4MB at all in latest
>OS X? I just spent a while trying what seemed every possible
>permutation of setting up /etc/sysctl.conf and editing /etc/rc directly,
>and it just fails (symptom: sysctl shows shmmax as -1, and Postgres
>cannot start).'
>
Is this perhaps one of the artificial limitations that they put in
place to make you buy Apple OSX Server?

Sincerely,

Joshua D. Drake

>
>Grrr. Apple's been pretty lame about this from day one, but at least
>it's been possible to do it one way or another.
>
>(Curiously, it seems you can now change shmall after bootup in 10.4.2,
>but that's not much help when you can't change shmmax.)
>
> regards, tom lane
>
>---------------------------(end of broadcast)---------------------------
>TIP 3: Have you checked our extensive FAQ?
>
> http://www.postgresql.org/docs/faq
>

"Luke Lonergan" <llonergan(at)greenplum(dot)com> writes:
> Yes - it's very strange, I've had the same experience though I finally found
> that setting SHMMAX and SHMALL to the same values, namely 268435456, seems
> to work out fine.

Interesting. I wonder if there's some bit of code that thinks that
SHMALL is measured in bytes (contrary to OSX's general convention
that it's measured in pages).

regards, tom lane

On Aug 29, 2005, at 8:18 PM, Tom Lane wrote:

> Has anyone been able to set kern.sysv.shmmax above 4MB at all in
> latest
> OS X? I just spent a while trying what seemed every possible
> permutation of setting up /etc/sysctl.conf and editing /etc/rc
> directly,
> and it just fails (symptom: sysctl shows shmmax as -1, and Postgres
> cannot start).
>
yeah, you need to set shmmax and shmall. shmall seems to be measured
in pages.
Here's the settings I've been using:

skittlebrau:/etc root# grep shm rc
# sysctl -w kern.sysv.shmmax=4194305 kern.sysv.shmmin=1
kern.sysv.shmmni=32 kern.sysv.shmseg=8 kern.sysv.shmall=1024
sysctl -w kern.sysv.shmmax=335544320
sysctl -w kern.sysv.shmmin=1
sysctl -w kern.sysv.shmmni=32
sysctl -w kern.sysv.shmseg=16
sysctl -w kern.sysv.shmall=327680

and just to verify:

skittlebrau:/etc root# sysctl -a | grep shm
kern.sysv.shmmax: 335544320
kern.sysv.shmmin: 1
kern.sysv.shmmni: 32
kern.sysv.shmseg: 16
kern.sysv.shmall: 327680

I've been running PG ith 10k shared bufs for a while.

The pain is sometimes /ec/rc gets rewritten :(

--
Jeff Trout <jeff(at)jefftrout(dot)com>
http://www.jefftrout.com/
http://www.stuarthamm.net/

In order to get postgres working in concert with an iSight on a
PowerBook, I had to increase shmmax, and it seemed to work just fine
by editing /etc/rc:

sysctl -w kern.sysv.shmmax=134217728 kern.sysv.shmmin=1
kern.sysv.shmmni=32 kern.sysv.shmseg=8 kern.sysv.shmall=1024

After restarting, I have:

# sysctl -a | grep shm
kern.sysv.shmmax: 134217728
kern.sysv.shmmin: 1
kern.sysv.shmmni: 32
kern.sysv.shmseg: 8
kern.sysv.shmall: 1024

Of course, this still doesn't seem to be enough to let postgres play
nicely with the iSight...

--
Thomas F. O'Connell
Co-Founder, Information Architect
Sitening, LLC

Strategic Open Source: Open Your i™

http://www.sitening.com/
110 30th Avenue North, Suite 6
Nashville, TN 37203-6320
615-469-5150
615-469-5151 (fax)

On Aug 29, 2005, at 7:18 PM, Tom Lane wrote:

> Has anyone been able to set kern.sysv.shmmax above 4MB at all in
> latest
> OS X? I just spent a while trying what seemed every possible
> permutation of setting up /etc/sysctl.conf and editing /etc/rc
> directly,
> and it just fails (symptom: sysctl shows shmmax as -1, and Postgres
> cannot start).
>
> Grrr. Apple's been pretty lame about this from day one, but at least
> it's been possible to do it one way or another.
>
> (Curiously, it seems you can now change shmall after bootup in 10.4.2,
> but that's not much help when you can't change shmmax.)
>
> regards, tom lane

Tom,

On 8/29/05 6:41 PM, "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Interesting. I wonder if there's some bit of code that thinks that
> SHMALL is measured in bytes (contrary to OSX's general convention
> that it's measured in pages).

I don't know, but I agree that the behavior has changed from Panther to
Tiger.

I wish BSD/Apple would go the way of Solaris 10 and be dynamic. This
ipc/shmem limits business has been a plague since its introduction.

- Luke

"Thomas F. O'Connell" <tfo(at)sitening(dot)com> writes:
> After restarting, I have:

> # sysctl -a | grep shm
> kern.sysv.shmmax: 134217728
> kern.sysv.shmmin: 1
> kern.sysv.shmmni: 32
> kern.sysv.shmseg: 8
> kern.sysv.shmall: 1024

> Of course, this still doesn't seem to be enough to let postgres play
> nicely with the iSight...

Don't you need to increase shmall too?

Also, which OS X release is this? 10.4 seems to have regressed
compared to 10.3 :-(

regards, tom lane

On Aug 29, 2005, at 10:37 PM, Tom Lane wrote:

> "Thomas F. O'Connell" <tfo(at)sitening(dot)com> writes:
>
>> After restarting, I have:
>
>
>> # sysctl -a | grep shm
>> kern.sysv.shmmax: 134217728
>> kern.sysv.shmmin: 1
>> kern.sysv.shmmni: 32
>> kern.sysv.shmseg: 8
>> kern.sysv.shmall: 1024
>
>
>> Of course, this still doesn't seem to be enough to let postgres play
>> nicely with the iSight...
>
> Don't you need to increase shmall too?
>
> Also, which OS X release is this? 10.4 seems to have regressed
> compared to 10.3 :-(
>
> regards, tom lane

This is 10.4.2. Everything worked as advertised. I didn't need to
increase shmall for the settings to stick, but maybe I ought to for
them to work.

--
Thomas F. O'Connell
Co-Founder, Information Architect
Sitening, LLC

Strategic Open Source: Open Your i™

http://www.sitening.com/
110 30th Avenue North, Suite 6
Nashville, TN 37203-6320
615-469-5150
615-469-5151 (fax)

Jeff - <threshar(at)torgo(dot)978(dot)org> writes:
> On Aug 29, 2005, at 8:18 PM, Tom Lane wrote:
>> Has anyone been able to set kern.sysv.shmmax above 4MB at all in
>> latest OS X?

> yeah, you need to set shmmax and shmall.

Did that. Set shmall first, shmall second, both together in one sysctl
command; no joy anywhere. Are you trying this on fully up-to-date
Tiger?

regards, tom lane

Tom,

On 8/29/05 9:37 PM, "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Did that. Set shmall first, shmall second, both together in one sysctl
> command; no joy anywhere. Are you trying this on fully up-to-date
> Tiger?

Did you try the values I sent earlier? If you set them both in
/etc/sysctl.conf and reboot, it should work. We get 100% repeatability on
10.4.2 platforms.

- Luke

This is from my Powerbook

in /etc/rc

sysctl -w kern.sysv.shmmax=5120000 kern.sysv.shmmin=1
kern.sysv.shmmni=32 kern.sysv.shmseg=8 kern.sysv.shmall=1024

I also had to up maxprocperuid to 200 to get buildfarm to run

I'm pretty sure shmall had to be increased to allow shmmax to be
increased.

Dave
On 30-Aug-05, at 12:37 AM, Tom Lane wrote:

> Jeff - <threshar(at)torgo(dot)978(dot)org> writes:
>
>> On Aug 29, 2005, at 8:18 PM, Tom Lane wrote:
>>
>>> Has anyone been able to set kern.sysv.shmmax above 4MB at all in
>>> latest OS X?
>>>
>
>
>> yeah, you need to set shmmax and shmall.
>>
>
> Did that. Set shmall first, shmall second, both together in one
> sysctl
> command; no joy anywhere. Are you trying this on fully up-to-date
> Tiger?
>
> regards, tom lane
>
> ---------------------------(end of
> broadcast)---------------------------
> TIP 2: Don't 'kill -9' the postmaster
>
>

On Aug 30, 2005, at 12:37 AM, Tom Lane wrote:

>
> Did that. Set shmall first, shmall second, both together in one
> sysctl
> command; no joy anywhere. Are you trying this on fully up-to-date
> Tiger?
>

Just ran software update and (besides a couple apps) it had a
security update.

skittlebrau:~ postgres$ grep shm /etc/rc
# sysctl -w kern.sysv.shmmax=4194305 kern.sysv.shmmin=1
kern.sysv.shmmni=32 kern.sysv.shmseg=8 kern.sysv.shmall=1024
sysctl -w kern.sysv.shmmax=335544320
sysctl -w kern.sysv.shmmin=1
sysctl -w kern.sysv.shmmni=32
sysctl -w kern.sysv.shmseg=16
sysctl -w kern.sysv.shmall=327680

skittlebrau:~ postgres$ sysctl -a | grep shm
kern.sysv.shmmax: 335544320
kern.sysv.shmmin: 1
kern.sysv.shmmni: 32
kern.sysv.shmseg: 16
kern.sysv.shmall: 327680

good luck.

--
Jeff Trout <jeff(at)jefftrout(dot)com>
http://www.jefftrout.com/
http://www.stuarthamm.net/

Jeff,

On 8/30/05 5:28 AM, "Jeff Trout" <threshar(at)torgo(dot)978(dot)org> wrote:

> Just ran software update and (besides a couple apps) it had a
> security update.

I just did that to test this.

> skittlebrau:~ postgres$ grep shm /etc/rc

Luke-Lonergans-Computer:~ lukelonergan$ cat /etc/sysctl.conf
kern.sysv.shmall=327680
kern.sysv.shmmax=335544320
#kern.sysv.shmall=268435456
#kern.sysv.shmmax=268435456

> skittlebrau:~ postgres$ sysctl -a | grep shm

Luke-Lonergans-Computer:~ lukelonergan$ sysctl -a | grep shm
kern.sysv.shmmax: 335544320
kern.sysv.shmmin: 1
kern.sysv.shmmni: 32
kern.sysv.shmseg: 8
kern.sysv.shmall: 327680

Thx for the tip.

I also tried different settings (shmall set to 500K) and shmmax ended up at
-1. So, it seems that shmall is in pages. I didn't try other allowable
configs, which was a problem before.

- Luke

[ resuming an old thread ]

"Luke Lonergan" <llonergan(at)greenplum(dot)com> writes:
> I also tried different settings (shmall set to 500K) and shmmax ended up at
> -1. So, it seems that shmall is in pages. I didn't try other allowable
> configs, which was a problem before.

I went back and experimented some more with this issue, and I believe
I've finally nailed down what the problem is: as of 10.4.something, OS X
rejects attempts to set SHMMAX to anything that isn't an exact multiple
of the page size (4096). Every other Unix on the planet, including
earlier versions of OS X, will round off the value to whatever unit
they feel like supporting ... but not Tiger. Thanks for this usability
improvement, Apple.

Also, the /etc/sysctl.conf file is utterly useless for setting SHM
settings in 10.4.2, because whatever it sets will be overridden by the
sysctl command that /etc/rc does just after reading /etc/sysctl.conf.
Perhaps in prior versions, the behavior was "first set wins" ... but
now it is definitely "last set wins". (SHMMAX eventually gets locked
down and can't be changed anymore; I'm not sure what triggers that,
but the sysctl in /etc/rc definitely gets to change what you put in
/etc/sysctl.conf.) Perhaps Apple can be persuaded to change the order
of these operations in /etc/rc, but until they do there is no point
in suggesting that people use /etc/sysctl.conf.

Bottom line: in 10.4.2, you have to edit /etc/rc to adjust SHMMAX,
and you'd better be sure it is an exact multiple of 4096.

I'll add a note about this to our documentation.

regards, tom lane