[ants_everywhere]

IO-bound doesn't mean it doesn't use much CPU. A tool can use a lot of IO and also a lot of CPU.

> then saving that tiny bit of CPU actually saved no money

this doesn't follow

> since it was already riding on the spare capacity of other investments

nor does this

Take for example a CLI that downloads and verifies the Bitcoin blockchain. It may spend most of its time downloading blocks, but it spends a ton of time calling SHA256 to verify those blocks. Similarly with a tool that downloads and checksums large files like Docker images.

If you have a fleet of 650K developer machines all running this util, then at some point it becomes cost effective to optimize the CPU usage.

Whether that point was reached in this example is not something I know. It seems like the L7 and their manager believed it was. But OP believes it wasn't. Either way, we don't know from OP's description of the situation.

[andrewflnr]

Sure, something like that is technically consistent with the description, but unlikely to be relevant. If you're thinking of a program that downloads a bunch of data and then does a bunch of cryptographic operations on it, what are the odds that the first description in your mind is "spends most of its time on HTTP requests"? Slim, I'd say, even if it's technically the majority of the time.

[ants_everywhere]

The question isn't the "hey what's the first description that comes to mind?" The question is why people on HN are mocking the idea that saving HUGE_NUMBER*B is a bad investment just because there is some other A satisfying A > B.

[andrewflnr]

Because B is quite possibly 0 in this case, given the limited information we have here.

[ants_everywhere]

The information we have is that an L7 and their manager believed the rewrite was valuable to the company

[mparnisari]

I was on that team. The rewrite was NOT valuable. Heck there is even a pinned Github issue at the top of the repo that tries to explain why this rewrite even happened and it doesn't have a good answer.

[andrewflnr]

And high ranking managers never make silly judgments based on hype or cool-factor, is that right? Come on, the overlying context was specifically the claim that upper level management had lost touch with reality, and that this was just one example.

[ants_everywhere]

I get that people want to make fun of management. But the complaints were that Amazon was stagnating and frugal. The idea that they're spending extravagantly on programming language fads is amusing, but isn't really consistent with what others were saying or with what we know about Amazon generally.

Rewrites to save compute resources are done pretty frequently at huge companies. It's a relatively easy source of projects for high level engineers because they can see the fleet-wide metrics and have figured out how to choose projects that have clear dollar value in their performance write-ups.

Could an L7 have wasted a bunch of time on a fruitless project? Of course. Could an L7 have wasted a bunch of time on a fruitless project at a notoriously cutthroat and frugal company AND be super proud of it? That seems much less likely since they have to show some numeric impact at that level, but I obvious still possible. Would their manager then also be proud of it? That seems even less likely.

So when the only description of the project also accurately describes a large class of valuable projects (i.e. decrease fleet-wide cost of a ubiquitous tool) I was genuinely curious if there was more to the story.