Urban Mainframe

PHP Caching to Speed up Dynamically Generated Sites

Jonathan Hollin — Sun, 07 Feb 2010 07:57:56 +0000

A nice introduction to dynamic page caching complete with source code.

WordPress, Caching and index.html

Jonathan Hollin — Sat, 06 Feb 2010 16:33:33 +0000

I became aware of an annoying little glitch on the Urban Mainframe yesterday. It seems that WordPress, on which this site is running, doesn't handle the URL http://example.com/index.html on an unmodified install (I've confirmed this on a handful of other WordPress sites). This is significant because index.html is a special file on many web-servers, often being the "home" page of a directory on the server. Without special handling, a request for index.html on a WordPress installation generates a 404 (file not found) error — which is obviously something we don't want our visitors to be presented with.

In my case the impact of the glitch was magnified because I employ a quite aggressive caching policy on this website — and yesterday an unlikely combination of factors resulted in my 404 error page replacing my home page for a complete cache cycle. It went something like this:

cached "home" page expires
next "home" page request is for http://urbanmainframe.com/index.html
index.html file request results in a 404 error
404 error page is cached
all subsequent requests for http://urbanmainframe.com/ — and other "home" page URLs — return the cached 404 error page until the cache is next invalidated

Quite a serious glitch then!

There are two things that shouldn't have happened here.

Requests for index.html should not result in 404 errors.
Error pages should never be cached.

I resolved the first issue by adding the following snippet of code to the very beginning of the 404.php file in my WordPress theme:

if ($_SERVER['REQUEST_URI'] == '/index.html') { header("Location: http://urbanmainframe.com/"); exit; } ?>
For the second issue I've filed a bug report with the authors of W3 Total Cache, which is the caching system I use here on the Urban Mainframe.

Kernel Level Root-kit

Jonathan Hollin — Fri, 29 Jan 2010 14:35:02 +0000

When do I get crazy-assed bikini models with sexual addiction issues lurking in the bushes? I think I could handle that. Instead, I get this tripe.

Hilarious mailing list exchange in which John C. Welch, who suffers no fools, goes from being helper to stalker in just four moves. Keep reading into the comments to see the inevitable appearance of a lawyer-wannabe (and his subsequent about-face). A must read.

Confessions of an Introverted Traveller

Jonathan Hollin — Fri, 29 Jan 2010 06:43:23 +0000

Sophia Dembling has a different style of travelling, and she’s tired of hiding it:

Introversion and extroversion are inborn traits, and the difference between them is not that one is gregarious and at ease in the world and the other shy and awkward. Rather, extroverts are outwardly motivated and gain energy from interaction with the outside world while introverts are more inwardly directed and drained by interaction with others. Introverts’ thinking tends to be deep and slow, we require copious time alone, we prefer probing conversation to shallow chitchat, and our social lives are geared more towards intimate one-on-one interactions than “more the merrier” free-for-alls.

Introducing the A4 Microprocessor, Apple’s First CPU

Jonathan Hollin — Thu, 28 Jan 2010 13:48:40 +0000

Apple's launch of the iPad didn't really rock my world. But, within the iPad presentation, there was a little something that got my spine tingling: Apple revealed that the iPad is powered by a heretofore unknown CPU - the A4.

To me this is much bigger news than the iPad itself. This is an Apple-developed CPU, which I think is a first for the company. Apple describe the A4 as a "1GHz custom-designed, high-performance, low-power system-on-a-chip." Early hands-on reports of the iPad seem to support this. One thing that is now well documented is that the iPad is very fast. Apple also claim run times of up to 10 hours and a standby time of up to 1 month for the iPad, so it's clear that the A4 is very power-efficient.

So what do we know or can reasonably assume about the A4?

We know it runs at 1GHz which, in the case of the iPad, results in a respectable performance. We know that, as a "system on a chip," it contains both a CPU (initial suspect is an ARM Cortex-A9 MPCore) and a GPU (most likely a PowerVR SGX series 5 - the ARM Mali has also been suggested). So it's multi-core capable and has a high-performance FPU. It's also OpenGL capable.

It's probably reasonable to anticipate that this chip, or its derivatives, will pop up in future iPods, iPhones and perhaps the Apple TV — along with any further mobile devices that Apple conceives — as well as the iPad and its future revisions.

I don't think that the processor, at least in this form, will appear in Apple's desktops or laptops — and it's not needed there either.

What's really exciting about the A4 is that it's a first attempt - yet it competes very favourably with the established mobile CPUs from the likes of Qualcomm, et al.

I'll bet the launch of the iPad has caused concern in the boardrooms of quite a few companies. It's going to be very interesting to see how this plays out.

Unify: A Fantasy Fulfilled

Jonathan Hollin — Wed, 27 Jan 2010 21:58:03 +0000

Ever since I first started making web pages, I wanted a CMS that would allow me to make content updates by simply going to my website and changing the content right on the page. My fantasy was that this system did not require me to know any programming language or tagging system beyond HTML and CSS and it didn’t require me to play with a database. In my fantasy, the system took minutes to implement and my clients could use it as easily as I could.

Apple iPad: First Thoughts

Jonathan Hollin — Wed, 27 Jan 2010 21:14:15 +0000

Apple have finally unveiled a tablet computer, the iPad. The anticipation leading up to this launch and the speculation surrounding it has been truly staggering. Yet I find myself strangely underwhelmed by the device.

Personally I have no need of a tablet computer, none at all. So this essay might appear to be a little negative. I was really hoping for something other than a tablet from this latest Apple event. So my heart sank as soon as Steve Jobs (who still looks awfully thin) mentioned tablets.

I followed the presentation via engadget's liveblog and I twittered my thoughts as the event unfolded. A slightly abridged transcript of my notes follows:

It's called the iPad...
I feel strangely disappointed - I've got no use for a tablet.
There's gotta be more to the iPad than this... surely... come on Steve, what are you holding back?
So far it all looks pretty standard stuff. It's like a big iPhone, but without the phone...
1GHz Apple A4 chip... whoa, that's new. Where the f*&^ did that come from?
Hmm... this chip could be the big news...
Runs all iPhone apps unmodified... yeah, yeah... blah, blah, blah... what about that chip?
Game graphics are really slick... So what's the A4 - a CPU, a GPU... is it both?
Still unimpressed with the iPad... waiting for the big news...
Unsurprisingly it's an e-book reader too. Nothing so far that hadn't been anticipated.
USB, Wi-fi and 3G...
No contract, unlimited data, deal with AT&T (US) @ $29.99/mnth. Euro deals in place June/July. All models unlocked, use GSM µSIMs
64GB + wi-fi + 3G = $829 = around £800 here in the UK. Naw, I'm not too keen. £299 would have been easier to swallow.
Ah... keyboard dock is interesting... now you've got a handy little portable terminal... now that's more like it.
Suddenly £800 (± a few quid) doesn't seem so bad. It's almost a netbook!!!
Wonder how well that screen copes with greasy fingerprints?
I'm really underwhelmed. The Apple guys are talking about a "magical device" at an "unbelievable price"...
... "our most advanced technology" and a "revolutionary device" - I can't help wonder, "am I missing something?"
No cameras, no GPS - so no augmented reality...
A missed opportunity methinks.
Silly me: of course geo-location can be achieved via 3G and GSM. Wouldn't expect that to be as accurate as GPS though.
Specs on Apple's website confirm that there is GPS.
There's Bluetooth too. So wireless sync with PC could be possible.
There is a camera connection kit too. So suddenly there's a few more possibilities.
1.6lbs and .5" thick - that's pretty good. It'll be easy to transport at least.
Okay. I'm somewhat intrigued. But I don't think I'll be rushing out to buy one. I'd prefer a MacBook Pro.
Back to that camera thing, despite the camera connection kit, augmented reality won't be too good without an integral camera.
So who is the iPad aimed at? What sort of customer does Apple see here, apart from the fan-boyz?
No multi-tasking on the iPad!!! Screen resolution 1024x768. First [hands on] reports tell us that it's really fast and responsive.
engadget reports that the on-screen keyboard is "good, not great. Not quite as responsive as it looked in the demos."

So there you have it. If you wanted a tablet then I'm sure you're jumping through hoops right now. But for myself, well I think I'll keep saving for that new MacBook Pro.

Unix Turns 40: The Past, Present and Future of a Revolutionary OS

Jonathan Hollin — Wed, 27 Jan 2010 15:53:09 +0000

After four decades, the future of the operating system is clouded, but its legacy will endure.

Regardless of the ultimate fate of Unix, the operating system born at Bell Labs 40 years ago has established a legacy likely to endure for decades more. It can claim parentage of a long list of popular software, including the Unix offerings of IBM, HP and Sun, Apple's Mac OS X and Linux. It has also influenced systems with few direct roots in Unix, such as Microsoft's Windows NT and the IBM and Microsoft versions of DOS.
The [Association for Computing Machinery] may have said it best in its 1983 Turing award citation in honor of Thompson and Ritchie's Unix work: "The genius of the Unix system is its framework, which enables programmers to stand on the work of others."

Monitor Applications, Processes and Files in OS X with opensnoop

Jonathan Hollin — Wed, 27 Jan 2010 13:56:21 +0000

Using the command line tool opensnoop you can track any Mac application's (or system process') usage of the file system. This is a very handy tool for administrators and troubleshooting! The simplest way to use it is as follows:

sudo opensnoop -n Safari

You can also track a specific file, and what is accessing it, like so:

sudo opensnoop -f /etc/hosts

Tracking a specific process is as simple as just specifying the process id:

sudo opensnoop -p PID

opensnoop will keep tracking the file until the process itself is ended, so just hit Control-C in the Terminal to stop opensnoop from running. In case you’re wondering, opensnoop is based on DTrace, a popular UNIX tool.

[via]

Awesome Studio Demo Reels

Jonathan Hollin — Wed, 27 Jan 2010 12:51:39 +0000

These stunning demo reels from Stargate Studios provide a little insight TV/movie production:

Urban Mainframe

PHP Caching to Speed up Dynamically Generated Sites

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WordPress, Caching and index.html

You might also enjoy:

Kernel Level Root-kit

Confessions of an Introverted Traveller

Introducing the A4 Microprocessor, Apple’s First CPU

You might also enjoy:

Unify: A Fantasy Fulfilled

Apple iPad: First Thoughts

You might also enjoy:

Unix Turns 40: The Past, Present and Future of a Revolutionary OS

You might also enjoy:

Monitor Applications, Processes and Files in OS X with opensnoop

You might also enjoy:

Awesome Studio Demo Reels