The Universe of Discourse
Sat, 05 Oct 2013

Today I was at the Pittsburgh Perl Workshop and I gave a talk because that's my favorite part of a workshop, getting to give a talk.

The talk is about Moonpig, the billing system that Rik Signes and I wrote in Perl. Actually it's about Moonpig as little as possible because I didn't think the audience would be interested in the details of the billing system. (They are very interesting, and someone who is actually interested in a billing system, or in a case study of a medium-sized software system, would enjoy a three-hour talk about the financial architecture of Moonpig. But I wasn't sure that person would be at the workshop.) Instead the talk is mostly about the interesting technical underpinnings of Moonpig. Here's the description:

Moonpig is an innovative billing and accounting system that Rik Signes and I worked on between 2010 and 2012, totaling about twenty thousand lines of Perl. It was a success, and that is because Rik and I made a number of very smart decisions along the way, many of which weren't obviously smart at the time.

You don't want to hear about the billing and accounting end of Moonpig, so I will discuss that as little as possible, to establish a context for the clever technical designs we made. The rest of the talk is organized as a series of horrible problems and how we avoided, parried, or mitigated them:

  • Times and time zones suck
  • Floating-point arithmetic sucks
  • It sucks to fix your mangled data after an automated process fails
  • Testing a yearlong sequence of events sucks
  • It sucks to have your automated test accidentally send a bunch of bogus invoices to the customers
  • Rounding errors suck
  • Relational databases usually suck
  • Modeling objects in the RDB really really sucks
  • Perl's garbage collection sucks
  • OO inheritance sucks
Moonpig, however, does not suck.

Some of the things I'll talk about will include the design of our web API server and how it played an integral role in the system, our testing strategies, and our idiotically simple (but not simply idiotic) persistent storage solution. An extended digression on our pervasive use of Moose roles will be deferred to the lightning talks session on Sunday.

Much of the design is reusable, and is encapsulated in modules that have been released to CPAN or that are available on GitHub, or both.

I went to sleep too late the night before, slept badly, and woke up at 6:30 and couldn't go back to sleep. I spent an hour wandering around Oakdale looking for a place that served breakfast before 8 AM, and didn't find one. Then I was in a terrible mood. But for this talk, that was just right. I snarled and cursed at all the horrible problems and by the end of the talk I felt pretty good.

Slides are available here. Video may be forthcoming.

Share and enjoy.

[ Addendum 20131217: I wrote up the talk contents in detail and posted them here. ]

[ Addendum 20131217: The video of the talk is available on YouTube, and has been since October, but I forgot to mention it. Unfortunately, the sound quality is poor; I tend to wander around a lot when I talk, and that confuses the microphone. Many thanks to Dan Wright for the video and especially for putting on PPW. ]

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