Semaphore numbers and system performance.

Semaphore numbers and system performance.

Post by Yibing W » Wed, 03 Jan 1996 04:00:00



We are thinking about re-configuring our HP9000/F20(817) server so it can support
more database instances.  To do that, we have to increase the number of semaphores
in the kernel.  Currently, we have 150 on that machine(the default value in
/etc/master file is 128).  I am wondering by increase that number to 200 what would
happen?  Will the machine get slow? By how much?

Thanks,

Yibing Wu

 
 
 

Semaphore numbers and system performance.

Post by Jeremy Le » Thu, 04 Jan 1996 04:00:00



>We are thinking about re-configuring our HP9000/F20(817) server so it can support

<snip> to increase the number of semaphores
<snip>
Quote:>happen?  Will the machine get slow? By how much?

<snip>

Increasing kernel parameters like this usually just allocate more table
space. This increases the memory usage of the kernel a tiny bit. You should be
more worried about the increased usage of the machine as a result of allowing
more database instances rather than the actual semaphores. Get some help
from hp to estimate the size (cpu/mem etc) of a machine that would be
required for the desired load and compare this with your machine. You may
need to budget for more memory for example.

Remember also that semaphores are used for locking, and increased usage of
locking increases the chance of short delays on occasions while processes
wait on semaphores.

As you might have gathered from this response - its one of those questions
that require an "it depends" type answer.

--
----------------------------------------------------------------------
Jeremy Lee
Wang Australia


 
 
 

Semaphore numbers and system performance.

Post by Chris Seo » Thu, 04 Jan 1996 04:00:00



> We are thinking about re-configuring our HP9000/F20(817) server so it can support
> more database instances.  To do that, we have to increase the number of semaphores
> in the kernel.  Currently, we have 150 on that machine(the default value in
> /etc/master file is 128).  I am wondering by increase that number to 200 what would
> happen?  Will the machine get slow? By how much?

> Thanks,

> Yibing Wu


Increasing the number of semaphores would NOT slow down the system. The
only thing it does will be to take up more system memory and hence
decreasing the amount of lockable memory on your system. Just make sure
that you don't over-allocate the resources so much so that there is
no more lockable memory available, and you'll discover that some of
your applications/programs that need lockable memory (like glance and
nettl) would not run.

Chris Seow
System Administrator
IRAS/CISB Unix Support Team