How Facebook Tells Your Friends You're Safe in a Disaster in Under Five Minutes
Monday, September 28, 2015 at 8:56AM
Todd Hoff in Example

Here's an article update: How Facebook's Safety Check Works.

In a disaster there’s a raw and immediate need to know your loved ones are safe. I felt this way during 9/11. I know I’ll feel this way during the next wild fire in our area. And I vividly remember feeling this way during the 1989 Loma Prieta earthquake.

Most earthquakes pass beneath notice. Not this one and everyone knew it. After ceiling tiles stopped falling like snowflakes in the computer lab, we convinced ourselves the building would not collapse, and all thoughts turned to the safety of loved ones. As it must have for everyone else. Making an outgoing call was nearly impossible, all the phone lines were busy as calls poured into the Bay Area from all over the nation. Information was stuck. Many tense hours were spent in ignorance as the TV showed a constant stream of death and destruction.

It’s over a quarter of a century later, can we do any better?

Facebook can. Through a product called Safety Check, which connects friends and loved ones during a disaster. When a disaster hits Safety Check prompts people in the area to indicate if they are OK or not. Then Facebook closes the worry loop by telling their friends how they are doing.

Brian Sa, Engineer Manager at Facebook, created Safety Check out of his experience of the devastating earthquake in Fukushima Japan in 2011. He told his very moving story in a talk he gave at @Scale.

During the earthquake Brian put a banner on Facebook with helpful information sources, but he was moved to find a better way to help people in need. That impulse became Safety Check.

My first reaction to Safety Check was damn, why didn’t anyone think of this before? It’s such a powerful idea.

The answer became clear as I listened to a talk in the same video given by Peter Cottle, Software Engineer at Facebook, who also talked about building Safety Check.

It’s likely only Facebook could have created Safety Check. This observation dovetails nicely with Brian’s main lesson in his talk:

Only Facebook could create Safety Check, not because of resources as you might expect, but because Facebooks lets employees build crazy things like Safety Check and because only Facebook has 1.5 billion geographically distributed users, with a degree of separation between them of only 4.74 edges, and only Facebook has users who are fanatical about reading their news feeds. More about this later.

In fact, Peter talked about how resources were a problem in a sort of product development Catch-22 at Facebook. The team for Safety Check was small and didn’t have a lot of resources attached to it. They had to build the product and prove its success without resources before they could get the resources to build the product. The problem had to be efficiently solved at scale without the application of lots of money and lots of resources.

As is often the case constraints led to a clever solution. A small team couldn’t build a big pipeline and index, so they wrote some hacky PHP and effectively got the job done at scale.

So how did Facebook build Safety Check? Here’s my gloss on both Brian’s and Peter’s talks:

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Article originally appeared on (http://highscalability.com/).
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