[rogerbinns]

This still doesn't answer why it is so large. Or more accurately my experience as a Netflix customer doesn't reflect the apparent size of all these backends. Compare to something like Reddit where every page is customised, I go through lots of them, and my interactions are frequent. My Netflix interactions look like recently viewed being custom, and everything else being generic (same for all users). If you told me my recommendations are recalculated once a month I'd believe you. The majority of time is spent viewing which is just periodic progress updates. In other words my user experience suggests Reddit having an infrastructure many times larger than Netflix.

[mryan]

I read that Netflix encodes each video 100+ times to ensure good performance across a wide range of devices. In addition to the "social network" side of the site (recommendations, what your friends watch, etc.) there is a lot of processing going on in the background.

[rogerbinns]

I vaguely recall the number being encoded 120 different ways. In any event this is independent of the number of users, and proportional to the amount of new incoming content. It also isn't real time, and doesn't really matter how long it takes other than marketing deadlines when they announce a new season of something far in advance.

The recommendations don't show any evidence of being calculated frequently, nor do they have to be done in real time. There is certainly way less appearing to go on than a site like Reddit.

"There is a lot of processing going on in the background" doesn't really answer the question :-)

[mryan]

Sure, this processing does not need to happen in real time, but it does need to happen.

My point was that to assume the user-visible portion of the site accounts for most of their computing needs is probably incorrect. Video encoding was just one of the first things I thought of, and I bet there are many more.

I admit "processing going on in the background" was a real hand-wavey way to phrase it, but I think you know what I mean. It's an iceberg - there's a lot happening under the surface. :-)

[cpwatson]

I don't work on the recommendations team but I feel I can safely say your recommendations are calc'd each day. Unfortunately I can't share more about our recommendation model other than to say its a strong business advantage.

[rogerbinns]

Still sidestepping what the heck all the machines are used for :-) You seem to be hinting that the majority is the recommendations, but even that shouldn't require such large scales. It also doesn't have to be that timely (eg it won't matter that much if the recalculations were once every 23 hours or once every 22). As a user it would be nice if this "strong business advantage" was useful.

[cpwatson]

"but no activity while actually watching things" is a false assumption. About 6-7% of upstream traffic at night in the US is Netflix...