Re: Need help debuging semaphores

On Fri, 13 Oct 2006, George Georgalis wrote:

> On Sat, Oct 14, 2006 at 03:38:15AM +0200, Claus Andersen wrote:
>> I am really at a loss and in doubt where too look for debuging. Any hints
>> would be _highly_ appreciated.
>
> what version of apache are you using?
> apache-ssl? mod_perl, mod_python?
> how about logging, are you using pipes
> or regular access.log?

apache-2.0.59
ap2-php5-5.1.5 (which broke my postgresql client 8.1)
ap2-py24-python-3.2.8
logging to access.log

> I think you need a custom kernel for
> apache-ssl with mod_python, extra semaphores
> or bigger block, don't remember exactly what

You are spot on! Thanks! I removed LoadModule python_module and apache 
starts.

The semaphores however bugs me as ipcs shows nothing.

> I did but it was just guess work because I
> couldn't find any doc on how to set them
> "correctly";

I found a lot of linux centric references to:
kernel.sem = 512 32000 32 512
...but none which explains what those numbers expands to.

The closest thing to an explanation was from a DB2 article:
"From here, modify the kernel parameters by adding the following entries 
to the /etc/sysctl.conf default system control configuration file:

kernel.msgmni =512
kernel.sem =250 128000 32 1024

where:

max semaphores system wide = max number of arrays x max semaphores per 
array."

Would that perhaps be something like:
SEGMNS = SEGMNI x ??

Anyhow I was getting ready to roll a new kernel with:
options        SEMMNI=1024       # number of semaphore identifiers
options        SEMMNS=1024       # number of semaphores in system

...when I got a little sidetracked - and I am glad I did!

My postgresql client recently got hosed with client 8.0 overwriting client 
8.1. I noticed that Postgresql didn't start because pg_ctl was the wrong 
version. I did a brute force replace of pg_ctl so Postgresql would start.

...and with postgresql running, apache does not choke on mod_python?!?

Results:
1) Apache runs fine without "LoadModule python_module"
2) Apache chokes with "LoadModule python_module" and postgresql not 
running. (_No_ other python references in httpd.conf - so no "SetHandler 
python-program")
3) Apache, mod_python is happy when postgresql is running.

It baffles me that there would be any kind of dependecy/relationship 
between mod_python and postgresql.

I am suspecting that postgresql might be tweaking the number of semaphores 
at run-time which causes the breakage of mod_python when it is not 
running.

I will try to confirm this by rolling a new kernel with more semaphores.

Kind Regards,
Claus Andersen