Notes from 20020328

Tue Apr 2 19:43:45 EST 2002

All,

	I forgot to put these up earlier....

	You may have noticed the lack of attributions for some of these
talks. That's because I don't know everyone's face - it may be a good idea
to mention your name if you want it in these notes :-)

----------------------
CLUG notes 28th March, 2002

- clustering, Ed Lang
 - for CBiS
 - Standard stuff, cheap machines etc etc
 - dual 1800+ Athlons
 - 3*1.6T  file servers
  - RAID 5-0, one spare
  - ~ 100MB/second
  - ext3
 - 15 processing nodes, 100GB scratch storage on each
 - separate login/auth server

 - Sun's gridengine
  - descendant of PCM, DQS
  - http://www.sun.com/software/gridware/

 - Problems so far
  - dense unit, not much room....
  - lack of funding

 - future
  - modular, slot more stuff in
  - hope the WD-120s don't fail!

- pghistory with Drake Diedrich
 - audit trails for PostgreSQL databases
 - with one of the above file servers
 - want to know who's changing what and when in postgres
 - retrieve previous values
 - databases which may need history
  - machine records,
  - licencing
  - major equipment tables
  - anything to do with money
 - what do you need for auditting?
  - triggers, rules, views
 - start with two tables
  - test, test_old
  - sequence number on old table
  - functions to insert into "old" table
   - timestamp
   - uid....
   - deleted flag
  - triggers copy old values out of table before inserting new data
  - use views to look at old data ("history views")

 - shell(?) wrapper to generate all of these tables, functions and views
 - something to convert old schemas as well
 - using postgresql from corporate desktops  OK

 - e.g. JCSMR licencing tables
  - 9 tables 
  - 7 under auditting control

 - no ref. integrity on old table
 - a lot like the old temporal and time-travel features of postgres

- An old program, interface to  apt called "console-apt" or "deity"
 - graphical interface
 - list of packages down the page
 - a number of revisions
  - perl
  - curse
  - ...
 - now a C++ program linking against the apt library
 - very similar to dselect
  - in look and feel
 - tree structure organisation of packages
  - full recursive dependency listing
 - filtering of package names
 - searching etc etc
 - similar functionality to apt-get, to get dependencies recursively
  - but includes a tetris game to keep you occupied
  - source of fsck (file system check) tetris?
   - not enabled by default.
 - not working too actively on it
 - GTK interface, too
  - lacks tetris, though
 - uses threads
  - continue doing stuff while it is downloading...
  - progress bars etc
 - multiple listings screens
  - flick between them
 - select actual version you want to install
 - dselect uses 18M of memory while running... at least
 - diety at 6M
 - aptitude 8.1M
 - problems getting debian to change away to another package manager
 - doesn't have the ability to "hold" packages

- XDM themes?
 - xdm is ugly
  - as it should be
 - when X starts, there are 8 steps
  - XDM starts
  - runs an xsetup file (as root) e.g. an x csonsole
  - login
  - x startup (as root)
  - xsession
  - X
  - logout
  - x reset script (as root)
  (goto 1)
 - hacking xsetup
  - shell script
  - before login prompt
  - xsetroot etc etc
   - call into themes directories
    - e.g. themes/foo/Xstartup

  - change symlink to change theme
   - packaging advice is to put these under /usr/share(?)
    - just not under /etc...
 - xtheme chooser
  - choose random theme

 - control the login box with xresources
 - random images
 - waiting for alpha in xfree86
  - transparency behing the login elements

- Brad Hards, Zeroconf networking
 - not about functional programming
  - no air guitar
   - even though it was written with emacs
 - networking with no admin staff
 - ad hoc networking
 - no-control-element networking
 - IETF working group
 - four protocol elements
  - IP interface cinfiguration
   - user group networking algorithm
   - seed random number generator with MAC
   - pick a random IP based on it...
   - ARP for the IP
    - If you get an arp response, choose another random number
   - do a few gratuitous arps to try to claim the IP address
   - wait for someone else to try to claim it
    - defend it if you need to
   - have a real IP address and zeroconf IP address
   - windows already does all this (98...)
    - with issues
    - strong defence in Windows 2000...
     - hammers other servers
     - will not cede an IP address
     - for when you join two networks
   - MacOS does it...
    - if DHCP fails
  - translation between hostname and IP
  - service discover
   - SMB does it naturally
   - e.g. random NFS file server
   - Service Location Protocol (rfc2608)
  - DNS
   - no central server....
   - multicast DNS (mDNS)
   - internet draft
   - might be in Bind 9.x
   - link-local multicast name resolution (LLMNR)
   - uses 224.0.0.251, port 5353
   - naturally susceiptible to DOS attacks
    - use a sep. cache for "normal" DNS
 - implementations
  - OpenSLP
  - ZCIP
  - ???

 - don't normally use it
  - useful for things like just plugging a USB cable thingy in and having it work.

 - SLP
  - uses multicast address
  - each machine can claim to provide certain services
  - "looks reasonably mature"
  - requests like "Who has home directories for fred and john"?

- shell interface to futexes, Rusty
 - Fast Userspace Mutexes
  -no contention, no talking to kernel
  - for fcntl locks, sysv semaphores etc
 - a few older implementaations...
 - linux threw the stuff in, went on holidays
  - this thing called POSIX threading....
   - doesn't work on futexes
  - e.g. mysql
 - reimplementing it... 6% slower, but...
  - waitqueues
  - e.g. counters going to one... put yourself on a wait queue
   - lots of nasty race conditions, solved in dodgy manners
    - put yourself on the waitqueue, see if you needed to, ...
  - two system calls
   - half as fast
   - Paulus suggests a single-call-for-most-common-case solution
    - is it this value?? Then cool...
 - read/write locks in userspace
  - backending to two futexes in the kernel
  - standard multiple readers/writers problem
  - furwlocks

 - next generation POSIX threading
  - researchy stuff in linux
   - no longer chasing other unixes....

 - fast read or grab userspace 

- Hotplug CPU, again with Rusty
 - nice machines allow hotplugging memory and CPUs
 - Rusty said at some conference that it shouldn't be too hard to do
 - ... and then pizza happened...

----------------------------------

With the zeroconf stuff - did anyone catch how you determine a gateway
for the network you're - kind of - on?

Yours,
-- 
Peter Barker                          |   N    _--_|\ /---- Barham, Vic 
Programmer,Sysadmin,Geek              | W + E /     /\                
pbarker at barker.dropbear.id.au         |   S   \_,--?_*<-- Canberra      
You need a bigger hammer.             |             v    [35S, 149E]   
qq%I've never heard of it or used it, apart from finding it in the Camel
 book and saying "Oh god".% -- Onceler