Comments on performance tuning kernel parameters

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From - Fri Apr 16 05:38:56 1999
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From: John Gray <johng@sodapop.org>
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Subject: Re: Scenario for the gurus
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Date: Thu, 15 Apr 1999 21:28:33 -0700
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AWKYOU wrote:

> First let me thank Tony and Joseph for their responses.
>
> I need some more detailed help.
>
> Scenario: A network is somewhat dishevled. The platform is SCO
> a new server is being purchased and will run SCO Openserver 5.0.5.
> There is the stong possibility of another server being installed running NT.
> The main unix application uses Informix databases. The NT server will most
> likely be running something which uses SQL server. FacetWin may also be
> currently running. Your clients are both Win 9.x,  NT workstations  and some
> Macs.
>
> You want to provide the fastest most reliable network possible   with all of
> the above characteristics and you get to start from scratch.
>
> What do you do?
>
> please include answers to the following in your response
>
> What  can VisionFS do that AFPS can't?
> What can  AFPS do that VisionFS can't?
> Does FacetWin mean no AFPS as one posting here indicated?
> NoTechnology supports appletalk does Openserver?
> Why use a product like FacetWin ( besides terminal emulation) when you have
> VisionFS or AFPS?
> Whats the minimum hardware requirements you would use for the NT server ;the
> SCO server (60 clients on the network).
>
> Thanks in advance

I apologize if this has been covered before.I can't speak for the network
applications but don't forget the kernel tuning.  It can really
help the database engine and remove the slugish behaviour of a system.

Above all don't skimp on your swap area if meory will be tight.

Openserver 5.05 will use by default 10% of your total memory for disk buffers
with a cap
of  about 6 meg by default.  Depending on how much memory you have you can
starve
the database engine.  This can be changed by running configure in
/etc/conf/cf.d.
    select  1 and then alter NBUF, each bufffer is 1K bytes.  NHBUF will auto
size so don't
    worry about that one.  If you have more  than   64 meg theres a good chance
you may
     want to raise this.

    By default PLOWBUFS  is 30 which will attempt to grab 30% of the space
allocated to
    your disk buffers and place them below 16 meg.   If your system is PCI you
won't need
    much except for maybe your floppy.    No more than a meg of low buffers
will be needed.

    Depending on how large your buffer cache is and how many temp files get
created and
     removed you may want to increase, decrease or leave alone  the BDFUSHR
parameter.
     This is how often the kernel scans the disk buffers and writes them out to
disk.  The default
     is once every 30 seconds which may be perfect for your needs but you can
always adjust it.
     For example if you do lots of compiles may raising it to 45 or 60 seconds
may work wonders
     but the down side is you leave your self more vunerable to disk corruption
if you have a
      kernel PANIC.

    Selecting option 2 will allow you to adjust GPGSLO and GPGSHI.  By default
the kernel will
    wait until there are about 25 pages (100k) left before it starts kicking
out dormant processes.
     ( hopfully dormant :-) )   It will then continue until there are 40 pages
free (160k).  If you are
    tight on memory this might be fine but if you have more RAM then you may
not want to wait
    around and bounce around the limit of your memory.  It's really an art that
is system specific
     but being a little more agressive with the GPGS lo and hi numbers may
prevent some disk
     thrashing.

      Option 7, since you are running a database, which may or may not have
many deamon running
       with it's user ID you may need to up MAXUP.  This is the number of
processes that can belong
      to one single user at a time.  When running large compiles I have found
that I need to up this to 500
       or my builds can fail.

      Option 12, NSTRPAGES.  by default it is set to 500 which is 2K.  If there
is heavy network traffic
       this can be raised also.  The pages are allocated as needed and this
number is a limit.   Using
       netsat -m to monitor the system during peak loads might give you a good
idea if it needs to be
       increased.  ( wierd error messages too)

       Options 13, 15 and 16 (messages queues, semaphores and shared data)
probably have some
       values that your database vendor  can specify in  the documentation
which is platform specific.
        Each database vendor will use these differently and the kernel defaults
are not optimal.

There is a good book that was written for 3.2V4 but has lots of good info which
details tuning your
system for databse performance.  It's  "The SCO Performance Tuning Handbook"
Gina Miscovich
 and David Simons.  ISBN 0-13-102690-9.    It was published in 1994.  Take this
into account when
 they talk about memory and cpu load.  The HW has changed a little.   :-)

Lastly I can't take much credit for what I have stated here.  I have learned
most of this from working
 with some very talented people.

hope it helps
-john

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