Engineers argue about algorithms. Then lose 200ms to a network call.
Every operation has a price. Roughly:
| Operation | Time | If 1 ns were 1 second |
|---|---|---|
| L1 cache read | 1 ns | 1 second |
| RAM read | 100 ns | 2 minutes |
| SSD random read | 100 µs | 1 day |
| Same-datacenter round trip | 0.5 ms | 1 week |
| Cross-continent round trip | 150 ms | 5 years |
Numbers this small mean nothing. So multiply everything by a billion:
Now look again. Your "small extra API call" is a five-year round trip.