Every ride-hailing platform eventually runs into the same wall. The matching logic that felt instant with a few hundred drivers starts to drag once a city fills up, and the slowdown shows up in the worst possible place: the seconds a rider spends staring at a spinner, deciding whether to close your app and open someone else's.
The problem was never the algorithm
Our first instinct was to make the matching smarter. Better scoring, tighter geofences, more signals per driver. That work mattered, but profiling told a less flattering story. Most of the time a rider waited was not spent deciding which driver to send. It was spent waiting on serialisation, on database round trips, and on a request path that did too much work per call.
Dispatch is a soft real-time system wearing the costume of a CRUD app. Once we started treating it that way, the bottlenecks were easier to find.
What Go bought us
We moved the dispatch path to Go for reasons that were boring and practical rather than ideological:
- Predictable latency under concurrent load, without tuning a garbage collector for every release.
- Goroutines that let us fan out driver lookups and collapse several sequential round trips into one parallel step.
- A deployment story simple enough that a single static binary runs the same way on a laptop and in production.
- A type system strict enough to make the hot path hard to accidentally slow down.
What we would do differently
We rewrote more than we needed to. The dispatch loop genuinely benefited from the move, but we carried along adjacent services that were never the problem, and we paid for that in review time and migration risk.
The lesson we took into later work: profile first, carve out the smallest surface that actually hurts, and leave everything else alone until it earns the rewrite. A rewrite that touches less is a rewrite you can ship.
Where this leaves us
Dispatch is no longer the part of Fary we worry about during peak hours, which means our attention has moved to the parts that now matter more — routing quality, driver supply, and the long tail of edge cases that only a live city produces.
