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Showing posts from May, 2014

Mad Memoization (or how to make computers make mistakes)

Memoization is a technique used to effectively cache the results of computationally expensive functions to improve performance and throughput on subsequent executions. It can be implemented in a variety of languages but is perhaps best suited to functional programming languages where the response to a function should be consistent for a given set of input values. It's a nice idea and has some uses but perhaps isn't all that common since we tend to design  programs so that we only call such functions once; when needed, in any case. I have a twist on this. Rather than remembering the response to a function with a particular set of values, remember the responses to a function and just make a guess at the response next time. A guess could be made based on the entropy of the input and/or output values. For example, where the response is a boolean value (true or false) and you find that 99% of the time the response is "true" but it takes 5 seconds to work this out, then...

Go-Daddy: Low TTL DNS Resolution Failures

Some of you may have noticed recently that  was not resolving correctly much of the time. At first I thought this was down to DNS replication taking a while though that shouldn't really explain inconsistent results from the same DNS servers (once picked up they should stick assuming I don't change the target (which I hadn't)). So eventually I called Go-Daddy support who weren't much help and kept stating that "it works for us" suggesting it was my problem. This despite confirmation from friends and colleagues that they see the same issue from a number of different ISPs. They also didn't want to take the logs I'd captured demonstrating the problem or give me a reference number - a far cry from the recorded message in the queue promising to "exceed my expectations"! But hey, they're cheap... Anyway... I'd set the TTL (Time To Live) on my DNS records to 600 seconds. This is something I've done since w

Sainsburys Glitch

A computer glitch at Sainsburys prevents delivery of some home orders. Caused by a... "computer fault". I doubt very much it was the computers fault though! It's highly unlikely it just forgot and rather more likely the poor thing broke a leg (disk), was knocked out (power outage) or was simply told to do something stupid by a piece of wet-ware  (either as an erroneous instruction or by design). Whatever... Once you've fixed the immediate issue then: Root-cause analysis. Determine the cost of incident. Estimate probability of it occurring again. Identify options to avoid in the future. Cost these options. Weigh the cost v benefit to see if anything should be done about it. And do it efficiently! Start with ballpark estimates and rules-of-thumb to see if the arguments have any merit before getting bogged down in the detail (but make these assumptions clear when you explain it to the boss!).

UK's security branch says Ubuntu most secure end-user OS (maybe)

Kind of late I know but I've recently completed a new desktop rollout project for a UK gov department to Windows 7 and found it interesting that CESG supposedly (see below) think that Ubuntu 12.04 is the most secure end-user OS . There was much discussion on this project around the security features and CESG compliance so I find this topic quite interesting. They didn't look at a wide range of client devices so other Linux distributions may prove just as secure, as could OSX which seems a notable omission to me considering they included ChromeBooks in the list. It was also pointed out that the disk encryption and VPN solutions haven't been independently verified and they're certainly not CAPS approved ; but then again, neither is Microsofts BitLocker solution. The original page under seems to have disappeared (likely as result of all the recent change going on there) but there's a lot on that site which covers end user device security including articles on

IE AppContainers and LocalStorage

IE's EPM (Enhanced Protected Mode) mode provides separate containers for web storage between desktop and Metro mode when using the Internet Zone. There's a page which discusses the detail but never really states why  it behaves like this. It seems to me that this is unnecessarily complex and will lead to user confusion and angst - "why does switching to desktop mode lose my session/cookies/storage?" or more simply - "why do I have to login again?". It's also arguably a security risk since users will have multiple sessions/cookies active so could inadvertently leave themselves logged in or could lead to duplicate transactions because items may be placed in the basket in separate containers etc. It would be less of a concern if users couldn't easily switch, but of course they can because MS has kindly put a menu item on the Metro page to "View in the Desktop"!? It all seems to be related to providing enterprise users with the ability to maint

Is lying the solution to a lack of privacy online?

I do wish social networking sites like G+ and FB would stop advertising peoples birthdays. Your birth date is one of those "known facts" used by many organisations (banks, government departments etc.) to verify your identity. Providing this data to social networking sites can result in information leakage and contribute to identity theft and security incidents. Combine this with all the other bits of information they capture and it would be quite easy for someone to bypass those security questions every call centre asks as a facade to security - they only need to gleam a little info from many sources. This morning G+ asked me if I wanted to say happy birthday to Peter. I know Peter slightly but not well enough to be privy to such information and I have no idea whether it really is his (or your) birthday today, if it is... Happy Birthday! If it's not then congratulations on lying to Google and Facebook - it's good practice (so long as you can remember the lies you tell

Windows 7 Incident

Having recently been responsible for an estate wide software upgrade programme for many thousand devices to Windows 7 I sympathise but have to find this amusing. However, it is an interesting approach to achieving a refresh in particularly short order... Make the best of it guys, treat it as an opportunity to audit your estate... I do hope your backup procedures are working though...  ;) Windows 7 Incident

Pre-emptive Single Task Operating System++

A while ago I wrote a blog entry about a pre-emptive single task operating system that I think the world needs. It seems I'm not the only one and George RR Martin (Game of Thrones) also thinks there's a need for this . His seems to stem from security as well as a productivity perspective but I think I grok what he means. The feature bloat in products such as MS Office these days detracts from their usability. They may be able to boil the ocean but it's not really necessary and just gets in the way of the creative process. However, DOS surely has a limited life and it must be hard to find the h/w components to run this on now. I may fire up a VM with DOS sometime to remind myself of the good-old-days... need-for-a-preemptive-os++


One of the things I have found irritating in the past is the need to install and configure a web-server each time the urge takes me to try something out. I don't run a local web-server permanently and being of a JFDI disposition the hurdle needed to get a server running is usually enough to stall what motivation I've managed to muster. Then I discovered that from Java 7 onwards it's fairly simple to implement your own web-server in plain Java - no need for an application server. LocalServe implements two types of handlers: 1. File-handler -  This serves any content (and sub-directories) in the directory in which localserve is run. Any file which is not found returns a 404 and  any request for the root of a folder (path ending in "/") attempts to return the index.html file in the directory. Note that localserve does not provide any listing of directories. If all you want to do is serve static content then the above is sufficient and LocalServe can be run using the

Entropy - Part 2

A week or so ago I wrote a piece on entropy and how IT systems have a tendency for disorder to increase in a similar manner to the second law of thermodynamics. This article aims to identify what we can do about it... It would be nice if there was some silver bullet but the fact of the matter is that; like the second law, the only real way to minimise disorder is to put some work in. 1. Housekeeping As the debris of life slowly turns your pristine home into something more akin to the local dump, so the daily churn of changes gradually slows and destabilises your previously spotless new IT system. The solution is to crack on with the weekly chore of housekeeping in both cases (or possibly daily if you've kids, cats, dogs etc.). It's often overlooked and forgotten but a lack of housekeeping is frequently the cause of unnecessary outages. Keeping logs clean and cycling on a regular basis (e.g. hoovering), monitoring disk usage (e.g. checking you've enough milk), cleaning up te

Feedback - Logging and Monitoring

It seems to me that we are seeing an increasing number of issues such as this reported by the Guardian . A lost transaction results in a credit default against an individual with the result that they cannot obtain a mortgage to buy a house. Small error for the company, huge impact for the individual. The company admitted that despite the request being submitted on their website they did not receive the request!? So either the user pressed submit then walked away without noting the response was something other than "all ok!" or the response was "all ok!" and the company failed to process the request correctly. If the former then, well, user error for being a muppet... As end users we all need to accept some responsibility and check that we get the feedback we expect. For the latter, there are several reasons why subsequent processing could have failed. Poor transaction management so the request never gets committed, poor process management so the request drops into s