From: swhite@tybse1.uucp (William C. "Spike" White)
Subject: Re: Xterminal-Server ratio wanted
Organization: Tybrin Corporation, Shalimar, FL
Date: Sat, 12 Sep 1992 20:13:12 GMT

In article <1836euINNaqs@early-bird.think.com> barmar@think.com (Barry Margolin) writes:
>In article <1992Sep1.200609.15078@progress.com> tucker@bedford.progress.COM writes:
>>	We are currently performing an initial investigation into upgrading
>>our present dumb-terminal based user environment to a X windows based one.
>>We are weighing all the dis/advantages of PCs, Xterminals and workstations
>>and look favorably at Xterminals from a maintenance standpoint. I use one
>>myself and see no lack of functionality. We would like any opinions on this
>>decision itself. And if we do go with Xterminals, then the question of how
>>many Xterminals running off of how many Sparcs, Sparc2s, Solbournes, etc. We
>>would like to hear about any success/horror stories about implementing such
>>a configuration and performance issues regarding Xterm/Server ratios which
>>seem to work well. These users will mainly be running Progress applications
>>and some word-processing, news readers and email UAs.
>
>What are "Progress applications"?

Applications built using the Progress database?

>
>My impression is that except for heavily graphics-oriented applications, an
>X terminal isn't much worse than a dumb terminal.  There's more overhead
>for keyboard input, but since that only happens at human typing rates, it's
>not really significant.  Output has some extra overhead, but unless you're
>doing it continuously (e.g. for animation), it's generally not enough to
>cause problems.  As far as the network is concerned, I'd guestimate about
>20-50% overhead for using X terminals over using dumb terminals (assuming
>the dumb terminals were on the network via a terminal concentrator).  I've
>never noticed any network congestion problems that I could attribute to X.
>
>As for server overhead, that also seems to be pretty low.  We some SS2's
>and multiprocessor SPARCservers with connections to two dozen X servers (a
>mix of X terminals, Sun workstations, and Macs running MacX) as well as
>some dumb terminals and Macs running Telnet, and at least one 4-processor
>690MP with connections to over 50 X terminals.  The main reason that X
>terminals tend to put more load on a server is that users tend to run more
>simultaneous applications; they'll have an xclock and xbiff running all the
>time, and they'll have several windows open rather than exit one
>application in order to start another.  You may need more swap space to
>hold all these active processes.
>
>If you're mainly going to be using text-based applications as you
>described, I think X terminals are definitely the way to go.

Here's a dissenting opinion.  

We ran an X11R2-based X-windows/Open Look system on a heavily-loaded database
server.  Even though we had a single X-terminal, we had to pull it off 
because the database performance would be terrible whenever any user used
the X-terminal.  The users weren't doing anything fancy, just two xterms and
1 graphics application.  Things would have been different if:
   1.  We had a modern version of X-windows (>= X11R4).
   2.  The server wasn't so overworked.
   3.  The server was faster (it was about a 10 MIPS machine).

In my opinion, X-terminals place a significant load on the server's resources
and should be figured in.  NCD has an excellent white paper called "Host
Loading in an X-terminal environment".  It has great rules of thumb for 
figuring the load on the server and the network.


-- 
Spike White     Tybrin Corporation, Shalimar, FL   | Moderation in all things --
spike.white@tybrin.com                             | and abstinence in none! 
Disclaimer:  The guys down the hall disagree with everything I say! Guess 
	     who speaks for the company. 
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