Re:Show HN: GraphCDN – GraphQL CDN with edge caching and ana...
by timsuchanek on Monday June 21, 2021 @06:16AM
(#27577810)
What do you mean by greater circle?
The circumference of the earth is 40,075,000 m.
Speed of light is 299,792,458 ms.
So we're talking about 40,075,000 / 299,792,458 = 0.1337 -> 134ms to get around the earth once.
As the earth is an ellipsoid that is mostly perfectly round, you can assume, that from any point A to B you'll just need to travel half of that, so we're at 67ms for light speed.
Looking at the 150ms now, which is about 2.3 times the 67ms, this kinda seems reasonable.
And yes, this is global purging - I just reconfirmed it with someone from Fastly.
Re:Show HN: GraphCDN – GraphQL CDN with edge caching and ana...
by kentonv on Friday July 02, 2021 @11:54AM
(#27713119)
That's the speed of light in a vacuum. The speed of light in fiber optic is slower.
Travelling half of the distance is not good enough, because if you haven't received _confirmation_ of the purge, then you can't trust that it really happened. There could be network errors, etc.
Sorry but it's not physically possible to do a global purge in 150ms.
Hmm, how can that be? Light in a straight-line fiber optic cable would take 200ms to traverse a greater circle around the world. Add some bends, relays, routers, not to mention servers, and it'll only get longer...
Are you sure the content is really being purged globally in that time, and not just from your local point of presence?
(Disclosure: I'm an engineer on Cloudflare Workers. I have no idea how Fastly does purges. Just trying to understand what you mean here...)