Seaside History

There are a lot of questions around the origins and evolution of Seaside, particularly after Avi and I gave up our old domain and the old Seaside and Seaside 2 websites with it.

A couple of months ago, I began (but never finished) a history page for the Seaside website to provide some background information for those who are interested. I had to dust off some of those notes to prepare my ESUG presentation on the past and future evolution of the framework and figured I might as well dust off the history page as well. So here's the story as best as I can recall it (and by "recall", I mean "find in Google" because Google seems to hold the majority of my memories these days).

[Update: now posted at seaside.st/about/History]

Introduction

Seaside made its public debut (version 0.9) in an announcement to the squeak-dev list on February 21, 2002. Avi Bryant and I developed Seaside to support our web application development consulting, specifically the development of a web-based theatre boxoffice sales system.

Seaside took heavy inspiration from Avi's Iowa framework (now here), which was written in Ruby and was itself inspired by NeXT's (and then Apple's) WebObjects. This first release of Seaside provided action callbacks for links and forms, session state management with support for call/return and the back button, and a component system with templates.

Experimentation

Almost immediately after the release of 0.9, we began work on Seaside 2.x (codenamed Borges, a reference to Jorge Luis Borges' short story The Garden of Forking Paths and an allusion to Seaside's support for forking session states). Seaside 2.0 was essentially a complete rewrite with a layered architecture: a Kernel layer providing a continuation-based HTTP request/response response loop and state (back-)tracking; a Views layer providing action callbacks and a rendering API for generating HTML; and a Component layer providing call/return semantics, embedding, and development tools.

Seaside 2.0 was released in October, 2003 with the templating system conspicuously absent. This was an experiment to see whether the development of the HTML rendering API and the wider acceptance of CSS had reduced or eliminated the need for templates. The new layered architecture made it easy for others to experiment with developing their own template engines. Seaside was also ported by Eric Hodel to Ruby, where it kept the name Borges.

Several versions followed in quick succession with major refactorings to the session state tracking and backtracking mechanisms. Seaside 2.3 (mid-2003) also introduced an even more layered architecture that tried to make some of the internals clearer and more accessibly to the project's growing number of users and contributors. It also confirmed that Seaside would not have built-in templates in the near future. Seaside became increasingly well-known around this time with a presentation at ESUG 2002 by Lukas Renggli and Adrian Lienhard and a hands-on development workshop at Smalltalk Solutions in 2003 by myself and Avi.

Stabilization

Seaside 2.4 and 2.5 addressed some growing pains in some of the core parts of the system: the Renderer API, collapsing under the weight of combinatorial explosion, was replaced by the now-familiar Canvas API; and some of the internal workings of the Session object were reified to make its application main-loop metaphor more obvious. Version 2.5 also saw the introduction of Component Decorations, Halos, and response streaming.

As first I and then Avi began to work full time developing applications using Seaside, the community began to carry more of the development load, with the release of Seaside 2.7 being  entirely (and very successfully) managed by the community, with Lukas, Philippe Marschall, and Michel Bany leading the effort. This release focused heavily on cleaning up the code base by fixing, deprecating, refactoring, and removing code.

ESUG 2008 Presentation

I'm in Amsterdam and just finished my ESUG 2008 presentation on the evolution of Seaside this morning. The gist of the talk was that Seaside has evolved through Experimentation, Stabilization, and Optimization and is enjoying a bit of an Adoption phase which should be encouraged. Sort of a call to arms.

I also took the opportunity to try to communicate the architecture and key metaphor of Seaside through illustrations. Finally, I rounded it all out with a few examples of less obvious (read badly documented) places people might consider extending the framework.

I think it went pretty well overall. I had a few people come up afterwards saying either that it had helped them understand some part of Seaside, that the historical perspective was interesting, or that they agreed with the need for documentation and advocacy.

I imagine James Robertson will post video on his blog at some point as he was filming all the talks. In the meantime he's posted a quick summary (wrong title and name spelled wrong, though! :) ). I'm guessing the slides will be available on the ESUG website sometime soon but I'll post them if not.

Update: Slides are available here.

RSS Feed Change

Just a quick note to anyone (Steve) who may be reading the feed for this blog: I've decided to start using FeedBurner, mostly just to provide email subscription for people who don't know what RSS means but also because I'm curious. I've been told that many news aggregators don't follow redirects, so you may need to update your feeds to the new URL: http://feeds.feedburner.com/BlogDotFitzellDotCa

And for anyone who would rather receive an email when there are new posts, use this link: http://www.feedburner.com/fb/a/emailverifySubmit?feedId=2122389&loc=en_US

Bash: using the read command

While I normally use awk or sed to pull a piece of information I want out of a line of text, it doesn't work as well when you need multiple pieces of information. Well it works fine for displaying multiple pieces of information, but if you want them in variables to use later?

I once wrote a script that used declare to do the equivalent of this:

declare `w | head -1 | 
  awk '{ print "DAYS=" $3 " " "USERS=" $6 }'`
  # now do something with $DAYS and $USERS

Ewww... Now I know there's a better way: the "read" command. You could do something like this:

w | head -1 |
  (read -a FIELDS
  #do something with ${FIELDS[2]} and ${FIELDS[5]})

You can also do like so:

ls -l | tail -1 |
  (read perms dunno user group \
      size month date year file
  echo "$user: $file")

You can even loop over all the lines of input. Let's take the /etc/passwd file as an example. Since that file uses a colon as a separator, we first need to set the IFS variable which determines what characters are used as field separators.

cat /etc/passwd | (IFS=:
   while read user pass uid gid desc theRest; do
      echo "$user: $desc"
   done)

As pointed out here, this is also one way to deal with a file containing a list of filenames that may have spaces in them:

cat list | while read f; do
  ls -l "$f"
done

Bash: printing the alphabet

(Sorry for the geeky topic, non-geeky readers)

Most have probably run across the "seq" command that will let you generate a list of numbers:

$ seq 1 4
1
2
3
4

But you can do similar with "echo" for a list of letters:

$ echo {a..d}
a b c d
$ echo {a..d}{a..d}
aa ab ac ad ba bb bc bd ca cb cc cd da db dc dd

Asterisk on VMWare

Many people have reported problems with Asterisk running on VMWare and having just decided to play with Asterisk I ran into them myself. First, here's what worked for me (using CentOS 4.6):

• On the VMWare host machine, edit the .vmx config file for your image and add:

host.noTSC = "TRUE"
ptsc.noTSC = "TRUE"

• In your CentOS image, disable the cpuspeed process:

chkconfig cpuspeed off

• Download and install the kernel-vm package from the CentOS test repos: http://dev.centos.org/centos/4/testing/i386/RPMS/
• Edit /boot/grub/menu.list and add the following boot parameters for the kernel-vm kernel: nosmp noapic nolapic

It actually worked fine for me without the extra kernel parameters but the CPU usage seemed to be slightly lower at idle with them added so I left them. The issue seems to be the default clock rate (1000Hz) used by most 2.6 kernels which can't be adequately serviced in the VM guests. The kernel-vm kernel is built with the clock rate at 100Hz.

Apparently CentOS 5 has a new kernel that allows you to specify divider=10 clocksource=acpi_pm to the kernel which tells it to run at 1/10 the clock rate it was compiled with.

Some links:
http://communities.vmware.com/message/762010#762010
http://bugs.centos.org/view.php?id=2189
http://communities.vmware.com/thread/101492?start=0&tstart=0
http://communities.vmware.com/thread/101406

Adjusting MTU to improve ADSL performance

So here I am in China, being driven mad by the number of dropped packets I'm seeing. Mostly it's not too bad until I make a VPN connection and then I'm seeing somewhere in the neighbourhood of 10% packet loss on a ping.

Well, after much, much debugging and internet searching I think I've finally found my problem: the MTU setting. MTU is the Maximum Transmission Unit or maximum size of an individual frame being sent on a network. Ethernet has an MTU of 1500, which is usually set as the default value for connections (at least in MS Windows). But other network equipment along your route may not be using Ethernet and may have a lower value. This is ok in theory; the equipment will break up larger frames into smaller ones and combine smaller frames into larger ones as the data is transferred between different networks.

The problem usually comes when your ISP's equipment is using an MTU slightly lower than your value. Apparently PPPoE connections always have a lower MTU than Ethernet (usually 1492) but Windows XP already accounts for that by reducing the MTU for PPPoE connections to 1480. In my case, though, China Telecom seems to be using equipment with an MTU of 1398.

What happens is that I send out 1480 bytes of data and China Telecom sends the first 1398 bytes and then holds onto the remaining 82 bytes until it gets some more data from me. Let's say I send another 1480 bytes. Now the first 1316 bytes of that frame are added to the 82 bytes from my first frame and sent and the remaining 164 bytes are held onto. This is slightly inefficient and can make the connection seem "bursty" because data is being held up before being sent. It also tends to get a lot worse if your connection is flaky (which mine is); I think this is because a lost frame along the way may hold part of the data for 2 or more of my original frames, all of which now need to be retransmitted. VPNs (because of the way TCP packets are being embedded into TCP packets) apparently amplify these effects further.

So how do we solve it?

Finding the Correct MTU

First, you need to find out what MTU setting your ISP is using. This MS KnowledgeBase article describes how to do this. Basically, you pick a host as close as possible to you on your routing path and run the following command:

ping -f -l size

The -f marks the packet as non-fragmentable and the -l size parameter specifies the number of bytes to include in the ping packet.

Start with a value of 1472 for size. If the ping is successful, your ISP's MTU is 1500. If you get the error Packet needs to be fragmented but DF set then decrease the value of size and try again. Once you find the highest value that allows a successful ping, that value plus 28 (20 bytes for the IP header and 8 for the ICMP header) is the correct MTU value.


Adjusting the MTU Value in Windows XP

Follow this KnowledgeBase article to set the MTU value for PPPoE (also seems to affect all VPN connections - not sure if there's a way to avoid that). Basically you want to set the following registry keys (all values are DWORD type):

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NdisWan\Parameters\Protocols\0]
ProtocolType = 0x00000800
PPPProtocolType = 0x00000021
ProtocolMTU = 1480

Obviously you would adjust the MTU value as desired and make sure to choose "decimal" when inputting the value. You probably have to reboot.

You may alternatively be ale to specify the MTU for the PPPoE interface here:

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\{Adapter-id/GUID}]
MTU = 1500

but I haven't tested it yet (again, adjust the MTU as desired and choose "decimal" when entering the value).

UPDATE: I tested setting the MTU for just the one PPPoE interface as above and it seems to work fine. I set the MTU value for NdisWan back to 1480 and will probably test removing that section from the registry altogether to see if it still works.

Other possibly helpful links:
http://www.speedguide.net/read_articles.php?id=157
http://www.speedguide.net/analyzer.php