Posts related to reliability

What does idempotent mean?

When you start to accumulate home theater components to go with your TV, you end up with a bunch of remote controls. One remote for the TV, one for the receiver, and one for the DVD/Blu-Ray player. One for a cable box, satellite, or set-top streaming box. Maybe you’ve got a multiple-disc CD player, or even a turntable. (Vinyl is making a comeback!) Maybe you’ve even still got a VHS?…no I’m kidding, nobody has those anymore.

The solution, rather than dealing with a stack of remotes, is to get one universal remote to rule them all. But once you do, you find that not all components are created equal, at least when it comes to the infrared codes (the actual signals sent by the remote control) that they accept.

A cheap A/V receiver might accept codes like PowerToggle or NextInput. These make it nearly impossible to reliably turn the unit on and set the right input, especially if someone has messed with the receiver manually.

A good receiver will have additional codes for PowerOn and PowerOff, even though those buttons don’t exist on the remote, and will also have an independent code for each input, like InputCable, InputSatellite, and InputBluRay.

This is the essence of idempotence. No matter how many times your universal remote sends the PowerOn and InputBluRay commands, the receiver will still be turned on and ready to watch Forrest Gump. PowerToggle and InputNext, however, are not idempotent. If you repeat those commands multiple times, the component will be left in a different (and unknown) state each time.

Third-order effects and software systems

At the height of the Cold War, the United States passed the Federal Aid Highway Act of 1956, giving birth to the Interstate Highway System. Fueled by the fear of foreign attack and the need to quickly transport troops and equipment across the continent, the network of protected access highways ended up transforming the nation’s economy and culture forever.

It was perhaps easy to predict a first-order effect: people would travel longer distances given the ease of doing so. A second-order effect was perhaps also easy to foresee: people would be much more likely to work or shop further away from home.

Fallacy #1: The network is reliable

Anyone with a cable or DSL modem knows how temperamental network connections can be. The Internet just stops working, and the only way to get it going again is to unplug it for 15 seconds. (Or, put another way, “Have you tried turning it off and on again?”)

Thankfully, better solutions exist for professional data centers than consumer-grade modems, but problems can persist.

As a company that does reliable messaging, we’ve really heard it all. Don’t worry, the names will be changed to protect the innocent.

The day we almost lost an invoice