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This is really unfair. This comment:

>A lot of Heroku's apparent value came from the intelligent routing feature. Everybody knew that it was harder to implement than random routing, that's why they were willing to pay Heroku for it.

is being addressed by Adam in this comment:

>Heroku's value proposition is that we abstract away infrastructure tasks and let you focus on your app. Keeping you from needing to deal with load balancers is one part of that. If you're worried about how routing works then you're in some way dealing with load balancing.

I think Adam is getting to a really fair point here, which is that nobody really minds whether the particular algorithm is used. If A-Company is using "intelligent routing" and B-Company uses "random routing," but B-Company has better performance and slower queue times, who are you going to choose? You're going to choose B-Company.

At the end of the day, "intelligent routing" is really nothing more than a feather in your cap. People care about performance. That's what started this whole thing - lousy performance. Better performance is what makes it go away, not "intelligent routing."




Intelligent routing and random routing have different Big O properties. For someone familiar with routing, or someone who's looked into the algorithmic properties, "intelligent routing" gives one high-level picture of what the performance will be like (good with sufficient capacity), whereas random routing gives a different one (deep queues at load factors where you wouldn't expect deep queues).

This is why it was good marketing for Heroku to advertise intelligent routing, instead of just saying 'oh it's a black box, trust us'. You need to know, at the very least, the asymptotic performance beavhior of the black box.

And that's why the change had consequences. In particular, RapGenius designed their software to fit intelligent routing. For their design the dynos needed to guarantee good near-worst-case performance increased with the square of the load, and my back-of-the-envelope math suggests the average case increases by O(n^1.5).

The original RapGenius post documents them here: http://rapgenius.com/James-somers-herokus-ugly-secret-lyrics

The alleged fix, "switch to a concurrent back-end", is hardly trivial and doesn't solve the underlying problem of maldistribution and underutilization. Maybe intelligent routing doesn't scale but 1) there are efficient non-deterministic algorithms that have the desired properties and 2) it appears the old "doesn't scale" algorithm actually worked better at scale, at least for RapGenius.

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>If A-Company is using "intelligent routing" and B-Company uses "random routing," but B-Company has better performance and slower queue times, who are you going to choose?

That's not the point.

As I think of it, "performance" is an observation of a specific case while intelligent/random can be used to predict performance across all cases.

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