[plug] LTSP server load

[Craig Ringer]

Hi all

I've had quite a number of questions over time about the load our LTSP 
server can take, given that we're equipping users with OpenOffice, 
Mozilla, etc. I thought I'd send a bit of info to [plug] for people's 
interest.

First: Interestingly, it turns out that users have the habit of closing 
apps after they're done with them, rather than just leaving the mail 
client etc open all the time. It seems strange to me, but what the hell. 
As a result, our memory load tends to be really silly - about 90% cache.

[craig ~]$ free -m
          total      used       free     shared    buffers     cached
Mem:     2015       1998         16          0        315       1422
-/+ buffers/cache:   260       1754
Swap:       0          0          0

with the following users logged in:

brenda
craig
leo
moira
olivia
rachael

And the load average is generally sillier:
[craig ~]$ uptime
  11:05am  up 21 days, 13:00,  3 users,  load average: 0.21, 0.12, 0.09
  11:19am  up 21 days, 13:14,  3 users,  load average: 0.14, 0.26, 0.20

(the 'user' count appears to be 'number of open xterms or other 
terminals' not 'number of logged in users' for some reason. *sigh*).

Results might be different, however, when users are regularly using 
OpenOffice and all users leave their mail open. Probably not much 
different, though. While top shows a memory footprint of ~43mb for the 
first OpenOffice instance, the real memory impact as measured by change 
in the output of 'free -m' appears to be about 9mb. Anybody who has 
ideas as to why has my ear.

23217 craig     15   0 44732  43M 35528 S     0.0  2.1   0:02 soffice.bin
23453 guest     15   0 44480  43M 35352 S     0.0  2.1   0:02 soffice.bin

but 'free -m' only shows a 9mb increase at each new instance.

The desktop (XFCE4) appears to use ~8mb of memory per instance according 
to change in free -m, but 76mb total if added up from ps output (RSS 
column). I'm confused.

Real world effect: adding a client may as well not have happened for all 
the difference it makes to the server. I wouldn't be surprised to be 
able to support 50 - 100 clients on this machine, though memory might 
become an issue then (depending on what the "real" memory use of our 
environment is).

Currently we have 6 - 7 users active at any one time, but this will be 
growing over time. I'm yet to migrate one user from our test LTSP 
system, for one thing. This system will probably be replacing ageing PCs 
in our journalist's/editorial section, and maybe even not-so-ageing ones 
if it works well there. No more win98!!

The staff love it, too. Then again, that's in part a matter of 
expectations. They came from win95 PCs with 16mb of RAM. Now they have 
Mozilla 1.3, OpenOffice 1.1rc1 (it's if anything more stable, faster, 
and just _better_), Acrobat Reader, etc. They can open huge JPEGs, PDFs, 
word documents, and even view EPSs. Their mail clients don't crash on 
large or strangely constructed messages, and they can view websites 
(FAST!). I've never had a single 'but it's different' since the first 
one went in, though there was some concern before that. Tunes quickly 
changed to 'when do I get /my/ new computer?' and "do I get a new screen 
with it? Oh well...".

The client machines are P133s and P100s with 32mb of RAM and Intel 
eepro/100 NICs. Some are PXE-booted, most are booted from a floppy disk 
and then netboot from there (but that'll be changing once we can get 
some bootroms for the NICs). There are some speed issues with 
text/fonts, but otherwise they're insanely fast. Large flash movies 
display with some, but little, lag. I wouldn't try video on one, but 
otherwise they're fine.

The server is a dual Xeon 2.4GHz with 2 gigs of RAM and a SATA RAID array.

Login environment is XFCE4, apps include OpenOffice, Mozilla, and (the 
main one) a remote xterm from our SCO OpenSewer box for our accounts & 
bookings system. XFCE was chosen because it's lightweight, easy to 
configure centrally, easy for users to modify but hard for them to 
ACCIDENTALLY change, and easy to fix if something goes wrong.

The only real issues we're having are an issue with mozilla mail 
sometimes 'jittering' when loading certain messages (see 
http://bugzilla.mozilla.org/show_bug.cgi?id=131733 ), mozilla 
occasionally crashing out when viewing or more often printing certain 
messages and OpenOffice's issues with complex word doc layout (because 
of /course/ Word is a DTP app... *sigh*). Some central configuration 
capability in OO.o and mozilla would be nice too - /etc/openoffice and 
/etc/mozilla dirs. It'd also be good to be able to have oo.o silently 
auto-install a workstation install when the user first tries to run it, 
but this isn't overly important. These issues add up to 'minor 
irritation' and are vastly outweighed by the cost, reliability, backup, 
and manageability improvements of the system.

OO.o is good enough that I'm considering using it for the journalist's 
computers, too. I'd have to turn off some autocorrect stuff, though. A 
good example: In oo.o, create a new text document and type
	I, somebody, blah blah <enter>

It'll turn the "I" into a roman numeral and the paragraph into a list 
entry. Overall, though, it's excellent and good enough to replace the 
win98 and Word 2000 setup the journalists have.

Oh... did I mention? The vast majority of that load average score is 
user screensavers ;-)

Craig Ringer