> From that perspective, fast search results aren't actually that exciting since you can constantly run a background task to update the cached results and just serve those as the requests come in.
If that's how it worked, I agree, it wouldn't be that impressive (every search result would just be a 1-1 cache lookup). That's not how it works, though, and as someone who works adjacent to the system, it is pretty impressive how fast it is when the work it's doing is actually pretty expensive.
Without caching, the cost of operating the site would dramatically escalate.
It gets tough with pages with 100k+ comments though, so there are different tricks and switches for different flows and data sizes.
Can't recall if it was "just" a bunch of FPGAs but it was a big-ass PCI card.
Some years later I tried to find this story again, and to check if they still used it. Turned out they had ditched it after just a couple of years. As memory sizes had increased, they could just precompute all possible routes for the next day and keep them all in memory...