I think my assumptions are just a lot more relaxed than yours. This isn't a trading platform I don't see why you need exactly-once write semantics.
> Not fanning out to up to 100 million inboxes.
https://en.wikipedia.org/wiki/List_of_most-followed_Twitter_...
There are only 6 users with 100m+ followers and they avg a lot less than a daily tweet. @BBCWorld is #50 and it drops to 38m accounts. #1000 has 2 million followers.
> And you think that's acceptable for a business valued in the tens of billions of dollars?
Elon by his own admission grossly overpaid for it. Twitter has hardly ever eeked out a profit, it is not worth tens of billions of dollars. Nothing much would happen if it went down for a bit except maybe bored journalists would report on it thus, as ever, driving even more users to the website. But that is neither here nor there.
More to the point: if Elon and Obama and Bibster tweeted in the same minute (what are the odds) you would, gasp, have to stagger the fan out of the updates. That's alright too, for Twitter. It isn't really actually real time.
Those follower counts are also grossly inflated and as you understand yourself only a small fraction of them are online using the app at the same time as the person is tweeting. By the time they do check they might never even see the tweet.
To the people offline you don't need to fan out in a timely manner.
In short I believe the write amplification is much closer to 1 million than 100 million even with the pathological cases. And beefy enough hardware can handle those peaks.
Here's another way to think about it: Elon has 118m followers and just posted twitter has 260m daily average users. He is a bit like Tom from MySpace, half the users on the website are subscribed to his updates (not exactly really but for simplicity).
I think it is perfectly alright if it takes a full minute until all those users see his latest meme. It is very unlikely that even a quarter of all his followers are using the app during that exact minute, so we're talking 30m writes in 60 seconds. Big whoop.
> You seem absolutely convinced that a massive social network can be run on a shoestring budget with tiny staff
I would bet a budget of say <$1 billion/year and 100 engineers for the core functionality as is.
> no amount of evidence from someone like me (who actually worked on this stuff in depth, and posts with my real name, and expertise in profile) will convince you otherwise
Neither one of us presented any evidence, just opinions as outsiders, as part of an informal conversation. An appeal to authority isn't an impressive argument, I am also from this industry and with similar experience.
There is no need to take things personally. I think we just have a very different estimation of just how much activity twitter sees at peak and how strict the requirements are.
