Re: Building Big Ass Linux Machine, what are the limits?

Alexander Kjeldaas (astor@guardian.no)
Fri, 25 Sep 1998 19:14:06 +0200


On Thu, Sep 24, 1998 at 10:48:39PM -0400, Jim McQuillan wrote:
> Hello all,
>
> I need to build a big machine to replace a
> Compaq Proliant running SCO OpenServer.
>
> The system needs to run several Progress databases (12gb and growing)
> and I am
> looking for maximum disk throughput for about 150 users accessing via
> Telnet.
>

I ran a Progress database on a Linux 486/66/32M that previously used
SCO in '97. It had about 10-15 concurrent users and was running
pretty well. It never crashed. However, I had to tune the kernel -
the number of semaphores and shared memory segments AFAIR. By
default, the Linux kernel isn't tuned for running large databases.

I would not recommend running SMP, but instead go for the fastest
single CPU machine you can get your hands on, they are pretty fast
these days anyway. Only if that doesn't work should you try SMP. You
can run Linux with up to 1G without tuning. If you need more memory,
you have to tune a few parameters. Using more than 3G is out of the
question for a database server since the maximum memory available to a
single process is 4G - physical memory.

I would also try both a 2.1 kernel and a 2.0 kernel. If the 2.1
kernel works for you, stick to it.

With 150 users you shouldn't run into maximum processes limit.
However, you should probably have some way of dealing with hung
connections. We had quite a bit of that on our Progress setup.

>From my own experiments, Linux deals pretty well with large number of
processes. At 2000 processes, fork()+exit() takes about 6x longer
than usual which isn't too good, but you shouln't have any problems
with it (2.3 will have constant overhead for large systems).

astor

-- 
 Alexander Kjeldaas, Guardian Networks AS, Trondheim, Norway
 http://www.guardian.no/

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