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Comment by dvt | Hacker News Reader

You're not missing anything. WhatsApp had 14 million active users with 32 engineers. Instagram had 30 million active users with 13 employees. It's just delusional to think you need four-figure engineers to run Twitter—a product that basically hasn't changed for over 15 years.

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I can't find it now, but someone in another post on Twitter pointed out that these comparisons aren't very meaningful: Twitter's social topology is any-any between users. A major (and unique) aspect of Twitter is that everybody on Twitter can talk to just about anybody else, and is encouraged to. This is also a critical value proposition for advertising on Twitter, and probably explains the size of their ads team.

This is very different from WhatsApp's topology, which is a relatively traditional chat system (small groups of shared state). Instagram's is closer, but still favors smaller social groups over a global feed.

Beyond that, Twitter is well known for running its own DCs, etc. It doesn't seem inconceivable that all of this, plus internationalization, mature platforms teams, etc. all adds up to four figures.

It boggles my mind how much people think "active users" is like some kind of fungible unit for engineering work required.

I don't think there's a inviolable ratio between active users and engineers, but you do absolutely need more engineers as your user base increases: you need more people on call, more people maintaining the servers you're running (especially if, like Twitter, you run your own DCs), more people doing QA and reliability engineering because of increased load, etc.

It's absolutely an OKR which implies higher workloads, are you kidding me‽ I'm sure you can build some architectural rat's nest where you need 100 engineers to maintain systems that barely serve a dozen requests a second (kind of like the blockchain) but that doesn't mean you couldn't do a much better job.

Everything else being equal, sure, more traffic is harder. But everything else is generally not equal. And despite your sleight of hand in this comment, your original claim about what's "delusional" was based on asserting an equivalence between the WhatsApp and Twitter workloads.

Sometimes it is, until you start comparing between wildly different companies and business models.

While the product looks like it hasn't changed much from the outside, it's been completely rewritten once or twice, at least. When Twitter launched it was a Ruby on Rails app. They scaled it to the absolute limit, then started breaking services away using Scala, then they kept at it adding several other languages to the mix.

While all this happened, there was almost zero product guidance. Instead, they watched for usage patterns, and started to incorporate those into the product. The original Twitter didn't have mentions, replies, or hashtags. Adding support for all that on a product not designed for it while managing exponential growth is an extremely difficult challenge.

On top of that, Twitter added divisions that are known to be engineer-heavy, such as ads, search, and infrastructure.

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The comparison with Whatsapp and Instagram is interesting. Whatsapp's case is special: they famously opted to use Erlang and it turned out to be a genius decision, as that allowed them to scale beyond expectations. Whatsapp never changed much from its initial design, which means no need for deep rewrites. Instagram was a Django app running on AWS servers, and that setup was enough until they got bought by Facebook and eventually moved from AWS to FB's infrastructure.

That does sound like a task for few dozen very skilled people per bigger system, not thousand+

Well, since you only have like 2 hours of productive work per week, thousands might still not enough.

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