Came across this on an internal blog and liked the description.
Think of good design in a system as a line of credit: just as purchasing new equipment for the business without generating income creates a debt against the credit line, adding features to a system without improving its design is “borrowing” against the capabilities of the system. There can be good reason to do this; after all, credit is used to improve cash flow and solvency. The danger is in thinking of this temporary loan as a permanent increase in funds. The debt must eventually be repaid.
Failure to reduce the debt (improve the design) in favor of making new purchases (adding new features) eventually results in a large portion of effort going toward interest payments (patches and bug-fixes), and reduced buying power (ability to add new features). Eventually, this can lead to a situation where all the effort is going toward interest payments (struggling to keep the system alive), and only trivial features can be added without major rework.
So last Thursday evening it was decided that I should go and collect my LadyFriend from her place of employment and transport her to my place of residence as she was not feeling well and did not need to endure the perils of public transport. The route home involves crossing the East Link bridge so I topped up my e-tag at about six thirty and headed off knowing that my vendor claims it takes up to 90 minutes to process the top up but Dublin traffic meant it would be two hours before I hit the toll bridge.
So two hours later I drive up to the toll barrier and get a lovely “account suspended” error. I had driven up to a barrier with a cash option as I feared that the 90 minute update interval was wishful thinking so I threw some cash in the basket and drove home. The next morning the LadyFriend was very much not well so after awhile I drove her back to work. At this point it was nearly midday so I was confident my top up would have been processed by then.
This was pure folly. “account suspended” flashed on the display once more. I had in a moment of misplaced faith in the NRA and NTR driven up to a barrier with no cash option and so caused some traffic delays while waiting for the Lady to come out and take my money. During this transaction a brief discussion ensued as to the length of time it takes an account update to be process. Two days is what she tells me. I am shocked. This is the kind of nonsense I expect from the banks but not from a modern system only put in place in 2007.
My gut reaction was that if someone was to propose a system design to me to implement that took more than 2 seconds to propogate updates from a tag vendor to a toll operator then something was seriously flawed with the design. I can only presume that the National Roads Authority and the various toll operators use carrier pigeons to implement their system.
After about a day of being this cocky about how I or any of the people I work with could do this much better I began to wonder how I would build it and so just to prove to myself that yes this could be done I have written up my design and included it below as it may prove of use to someone.
Only read beyond this point should you actually be interested in how I would build this system and actually think things like message queuing and distributed systems are fun.
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I was having lots of problems last night and this morning with multicast not working correctly on a linux host. As soon as I started tcpdump multicast would work. It is not fun trying to troubleshoot a problem that goes away everytime you try to debug it.
Turns out the realtek r8169 driver doesn’t handle multicast on the newer cards correctly.
Downloading the r8168 driver from Realtek and installing it resolved the issue.
This post is being made so that google will be able to help the next person with this problem.
In a move that caught everyone by surprise including myself I asked my Ladyfriend to marry me while we were in Rome last week. Following only the briefest of pauses to exclaim surprise the Lady said yes.
So while attempting to copy all my photos from the Trans Canadian train journey onto my laptop it started whining about low disk space. It seems I have managed to produce somewhere in the region of 25GB of photos so far and there is another week to go. My short term plan is just to buy some blank dvds in Portland but how do people store all their photos.
Whats the first thing to do in New York. Thats right a trip to the B&H Super Store on 9th Avenue to buy some bits and pieces for my EOS 400D. The initial shopping list was short, just one lens and a flash but with the fact that things are much cheaper in the states plus the extra bonus from the strong euro the list started to grow just a tad. As part of my tidying things up in work before the trip I submitted the expenses claim of doom. From the beginning of September last until the end of June. It was a hunk of change and was my budget for camera shopping while in New York.
Yes that man does have a screwdriver in his face.
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So the flight over was ok but really Aer Lingus what were you thinking, “Showbands 2″ is not an acceptable thing to show to mass murderers let alone tourists who we want to actually remember Ireland fondly. Besides the poor entertainment options the flight was uneventful, just long. It seems I am not cut out for long haul.
Thursday was a bit hectic with trying to make sure I had most of my work stuff handed over to other people and doing things like learning how to setup my voicemail, “Hi this is colin, …”, along with one of those silly out of the office messages on my email. I have not yet gotten used to being without my phone.
So Boston is pretty snazzy and warm, so very very warm. It is Harborfest this week so lots of Tea Party recreation and similar going on. The Chowderfest tomorrow should be most enjoyable. Anyway it is nearly time to meet one of the Ladyfriend’s scary internet friends so until next time.
Live from the count at the RDS
After sitting through Eoin O’Dell (photo below) talking about the legal challenges facing bloggers I am tempted never to post anything on the internet ever again. Barcamp was good fun and I was sorry to have to leave early and miss some of the later talks that I was interested in. Hopefully those who came to my talk got something useful from it.
This was orignally ment to be a write up myself and Peter’s adventures at LAMM last year but I never quite got arround to posting it. This years lamm is fast approaching and I have yet to enter because Peter is not able to take part this year due to PHD deadlines so I need to find a new partner.
If anyone reading thinks 2 days running about the scottish highlands sounds fun check out the LAMM website and see if you would be comfortable doing the novice class.