• Number of seconds:
    • 1 day: 100k
    • 1 month: 2.5M
  • Number of users:
    • USA: 300M
    • Social networks (i.e. daily active users):
      • Facebook: 2B
      • YouTube, WhatsApp: 1B. (YouTube hasn’t published its DAU but it’s definitely going to be more than Instagram’s, so 1B should be fine.)
      • Instagram: 500M
      • Snapchat, Twitter: 200M
      • Reddit: 50M
    • Proportion of users who create vs consume: 1%
    • 80-20 rule: 20% things get 80% traffic. So, assume cache rate of 20%.
  • Machine:
    • Number of connections an average modern server can handle: 50k
  • Latency (see more here, ignore other Google search results as the numbers there are outdated):
    • Read 1MB from:
      • Memory: 3 us
      • SSD: 50 us
      • Disk: 825 us
    • Network round trip:
      • Same data center: 0.5 ms
      • Halfway across the earth: 150 ms
  • ID:
    • Assume number of bytes for a string = 2 * length.
    • Assume you use [a-z, A-Z, 0-9] to generate your IDs. Then 62^8 is a huge number that should suffice for most use cases.
    • UUIDs are 16 bytes.
  • Bytes:
    • KB =1e3 bytes.
    • MB = 1e6 bytes.
    • GB = 1e9 bytes.
    • TB = 1e12 bytes.
    • PB = 1e15 bytes.