4 ms·

> Even programmers and IT professionals have literally not mental model of how fast computers really are. Or of how slow light is!

deleted 3y ago
[deleted]
paulddraper 3y ago
Exactly. Speed of light is not exactly a relatable point of reference.
- jiggawatts 3y ago
  It ought to be intuitive for everyone working in software development! The performance of everything is limited in one way or another by ‘c’. Not just WAN links, but the data centre Ethernet as well. The distance to the disks matters. The physical size of the motherboard. The placement of caches, etc… When people say things like “putting the compute near the data” they’re implicitly talking about overcoming the limits imposed by the speed of light. When you hear about an N+1 performance issue in some ORM, that’s bad because of the speed of light. When you test your LAN with “ping”, you’re lying to yourself because it won’t show measurements below 1 ms, which is an eternity. I just told you how much compute can occur in just 10 nanoseconds. Go ping something. Look at the “1 ms” in the output. Go back to my post and work out what can occur in 1,000,000 nanoseconds. Go look at the 1 ms again. Repeat until you have an epiphany about your zone redundant Kubernetes-hosted cloud native microservices architecture.
  - deleted 3y ago
    [deleted]
  - BenjiWiebe 3y ago
    FYI the ping utility in linux shows 3 significant figures. On my lan it's reporting 0.156ms avg between two hosts.
    - jiggawatts 3y ago
      150 microseconds is typical, but for reference, Azure gets about 85µs between VMs in proximity placement groups, and I've heard of single-digit latencies with high-end RDMA NICs. Your ping is 156,000 nanoseconds. You just saw that you can in principle do about 6,400 computations per 30ns, so... that's about 33 million arithmetic calculations per round-trip, within the data centre. I hope this makes you see every unnecessary network hop in a different light. PS: It typically takes 3 round-trips to establish a TCP connection, and 5-7 for a TLS connection. A database connection over TLS needs a few more. And then you have load balancers, firewalls, proxies, envoy, ingress, dapr, and, and, and...
  - Dylan16807 3y ago
    Speed of light between datacenters is important. Datacenter Ethernet has too much overhead to make a difference in almost all cases. Disks have an even higher overhead:distance ratio. The size of a motherboard only matters for signal integrity, not that half a nanosecond extra. Cache location inside a chip can matter, but even then size is a significantly bigger factor than location.
- dylan604 3y ago
  Except we know nothing is faster than light, so that's a reference people know
  - pyinstallwoes 3y ago
    Unless you don’t measure it, then it’s as fast as it needs to be! Oh group velocity.
elboru 3y ago
This site[0] helped me improve my mental model. You can scroll through the solar system at scale (the moon being one pixel). It takes a while!! Then you notice a small button at the right bottom corner, that button allows you to auto-scroll at the speed of light, wow, now that’s slow! [0]https://joshworth.com/dev/pixelspace/pixelspace_solarsystem.html https://joshworth.com/dev/pixelspace/pixelspace_solarsystem....
- nomel 3y ago
  Makes you realize that space travel isn't going to happen with current physics.
  - deleted 3y ago
    [deleted]
  - porphyra 3y ago
    The faster you go, the shorter you have to travel due to length contraction. So travelling really far distances is still possible, for example, by constant acceleration [1]. It's just that everyone you left behind will have been dead for billions of years by the time you arrive. [1] https://en.wikipedia.org/wiki/Space_travel_under_constant_acceleration https://en.wikipedia.org/wiki/Space_travel_under_constant_ac...
    - nomel 3y ago
      > for example, by constant acceleration Yes, this is why it won't happen, with our current understanding of physics, and the practical limitation that implies, with the resources we have. ;)
    - bitwize 3y ago
      > It's just that everyone you left behind will have been dead for billions of years by the time you arrive. sad piano plinks https://www.youtube.com/watch?v=kEVZ3NIoEAE https://www.youtube.com/watch?v=kEVZ3NIoEAE
    - rsaesha 3y ago
chrismorgan 3y ago
I’m an Australian. A lot of the internet I interact with is in America, and a lot of the rest is in Europe. These are all hundreds of milliseconds away by fibreoptic cable, the latency of which is proportional to the speed of light. I’ve been to America a few times. The internet is so fast there: not because of bandwidth differences, but because of latency, and especially sites carelessly loading chains of resources, which amplify the effects. As soon as you deal in intercontinental stuff, you realise just how slow light is. (As for studies in the effects of page load abandonment, those are never in the slightest bit relatable—at the time those studies suggest half the people are giving up, most sites still haven’t rendered anything at all, here.)
- citrin_ru 3y ago
  Speed of light is the lower bound for network latency but actual internet latency also significantly affected by delays added by network equipment (routers/switches). Typically the bigger distance the more routers there are in between so this delay is also proportional to the distance. And sometimes there are almost saturated channels so there is a significant queuing delay for packets waiting to be sent. RTT AU <-> US will be higher than RTT for most pairs inside the US but RTT for the same distance within the US can vary more than 3x depending on exact network infrastructure on the way.
  - Cold_Miserable 3y ago
    Using fibre-optic cable where light travels in a zig-zag instead of using lasers increases latency too.
jebarker 3y ago
I recently encountered this from both sides in my work. I was trying to get a particular single-threaded CPU program running in less than 1 microsecond. Light goes about 300m in that time. I remember reading around the same time that the Eiffel Tower is about 300m tall. So it stuck in my head that if someone switched a flashlight on at the bottom of the Eiffel Tower at the same time as my program starts the program should complete before someone at the top of the tower sees the light.

deleted 3y ago

[deleted]

paulddraper 3y ago

Exactly. Speed of light is not exactly a relatable point of reference.

jiggawatts 3y ago
It ought to be intuitive for everyone working in software development! The performance of everything is limited in one way or another by ‘c’. Not just WAN links, but the data centre Ethernet as well. The distance to the disks matters. The physical size of the motherboard. The placement of caches, etc… When people say things like “putting the compute near the data” they’re implicitly talking about overcoming the limits imposed by the speed of light. When you hear about an N+1 performance issue in some ORM, that’s bad because of the speed of light. When you test your LAN with “ping”, you’re lying to yourself because it won’t show measurements below 1 ms, which is an eternity. I just told you how much compute can occur in just 10 nanoseconds. Go ping something. Look at the “1 ms” in the output. Go back to my post and work out what can occur in 1,000,000 nanoseconds. Go look at the 1 ms again. Repeat until you have an epiphany about your zone redundant Kubernetes-hosted cloud native microservices architecture.
- deleted 3y ago
  [deleted]
- BenjiWiebe 3y ago
  FYI the ping utility in linux shows 3 significant figures. On my lan it's reporting 0.156ms avg between two hosts.
  - jiggawatts 3y ago
    150 microseconds is typical, but for reference, Azure gets about 85µs between VMs in proximity placement groups, and I've heard of single-digit latencies with high-end RDMA NICs. Your ping is 156,000 nanoseconds. You just saw that you can in principle do about 6,400 computations per 30ns, so... that's about 33 million arithmetic calculations per round-trip, within the data centre. I hope this makes you see every unnecessary network hop in a different light. PS: It typically takes 3 round-trips to establish a TCP connection, and 5-7 for a TLS connection. A database connection over TLS needs a few more. And then you have load balancers, firewalls, proxies, envoy, ingress, dapr, and, and, and...
- Dylan16807 3y ago
  Speed of light between datacenters is important. Datacenter Ethernet has too much overhead to make a difference in almost all cases. Disks have an even higher overhead:distance ratio. The size of a motherboard only matters for signal integrity, not that half a nanosecond extra. Cache location inside a chip can matter, but even then size is a significantly bigger factor than location.
dylan604 3y ago
Except we know nothing is faster than light, so that's a reference people know
- pyinstallwoes 3y ago
  Unless you don’t measure it, then it’s as fast as it needs to be! Oh group velocity.

elboru 3y ago

This site[0] helped me improve my mental model. You can scroll through the solar system at scale (the moon being one pixel). It takes a while!! Then you notice a small button at the right bottom corner, that button allows you to auto-scroll at the speed of light, wow, now that’s slow! [0]https://joshworth.com/dev/pixelspace/pixelspace_solarsystem.html https://joshworth.com/dev/pixelspace/pixelspace_solarsystem....

nomel 3y ago
Makes you realize that space travel isn't going to happen with current physics.
- deleted 3y ago
  [deleted]
- porphyra 3y ago
  The faster you go, the shorter you have to travel due to length contraction. So travelling really far distances is still possible, for example, by constant acceleration [1]. It's just that everyone you left behind will have been dead for billions of years by the time you arrive. [1] https://en.wikipedia.org/wiki/Space_travel_under_constant_acceleration https://en.wikipedia.org/wiki/Space_travel_under_constant_ac...
  - nomel 3y ago
    > for example, by constant acceleration Yes, this is why it won't happen, with our current understanding of physics, and the practical limitation that implies, with the resources we have. ;)
  - bitwize 3y ago
    > It's just that everyone you left behind will have been dead for billions of years by the time you arrive. sad piano plinks https://www.youtube.com/watch?v=kEVZ3NIoEAE https://www.youtube.com/watch?v=kEVZ3NIoEAE
  - rsaesha 3y ago

chrismorgan 3y ago

I’m an Australian. A lot of the internet I interact with is in America, and a lot of the rest is in Europe. These are all hundreds of milliseconds away by fibreoptic cable, the latency of which is proportional to the speed of light. I’ve been to America a few times. The internet is so fast there: not because of bandwidth differences, but because of latency, and especially sites carelessly loading chains of resources, which amplify the effects. As soon as you deal in intercontinental stuff, you realise just how slow light is. (As for studies in the effects of page load abandonment, those are never in the slightest bit relatable—at the time those studies suggest half the people are giving up, most sites still haven’t rendered anything at all, here.)

citrin_ru 3y ago
Speed of light is the lower bound for network latency but actual internet latency also significantly affected by delays added by network equipment (routers/switches). Typically the bigger distance the more routers there are in between so this delay is also proportional to the distance. And sometimes there are almost saturated channels so there is a significant queuing delay for packets waiting to be sent. RTT AU <-> US will be higher than RTT for most pairs inside the US but RTT for the same distance within the US can vary more than 3x depending on exact network infrastructure on the way.
- Cold_Miserable 3y ago
  Using fibre-optic cable where light travels in a zig-zag instead of using lasers increases latency too.

jebarker 3y ago

I recently encountered this from both sides in my work. I was trying to get a particular single-threaded CPU program running in less than 1 microsecond. Light goes about 300m in that time. I remember reading around the same time that the Eiffel Tower is about 300m tall. So it stuck in my head that if someone switched a flashlight on at the bottom of the Eiffel Tower at the same time as my program starts the program should complete before someone at the top of the tower sees the light.