Real-time commenting across the site has been live for about two weeks now, but Facebook has only confirmed the new feature today.
Though it seems nothing but natural for Facebook to abandon asynchronous conversations in favor of more fluid, spontaneous discussions, the new feature revives, in my mind, the old Facebook versus Twitter fight. Ordinarily, the two can be easily distinguished: the former is a social network for sharing with friends and the latter is an information network for sharing with the world.
In implementing a more real-time comment system, however, Facebook appears to be leaning a little bit more towards Twitter’s model, which focuses on discussions in the now. Of course, there’s still that one major distinction: Facebook is by default a private network, whereas Twitter is by default very public. Still, it’s always interesting to see one borrow ideas and features from the other.
By the way: anyone who thinks implementing a synchronous conversation system should be simple probably isn’t an engineer. If you head over to the Facebook engineering site, you can read about all the nitty gritty complications that went into designing the live commenting feature. Unsurprisingly, the biggest issue was creating a system that would work well at Facebook’s scale.
Writes Facebook software engineer Ken Deeter:
So we needed a push-based approach. To be able to push information about comments to viewers, we need to know who may be viewing the piece of content that each new comment pertains to. Because we serve 100 million pieces of content per minute, we needed a system that could keep track of this "who's looking at what" information, but also handle the incredible rate at which this information changed.
Deeter says the new comment system originated at a Hackathon event and eventually grew into a site-wide feature.