assist.uz
A booking app for pickup football games, and a small lesson in what happens when twelve people tap the same button on the last open spot.
The idea
Pickup games in Tashkent get organised in group chats, which works until a game is nearly full and nobody can tell who is actually in. The app does one thing: shows open games nearby and lets you claim a spot.
The interesting part
The last spot. Naive booking logic reads the remaining capacity, decides there is room, and writes the booking — and under concurrent requests, several of those reads happen before any of the writes. The game ends up oversubscribed and somebody arrives to find no place for them.
The fix was to move the decision into the database: a conditional write against remaining capacity inside a transaction, so exactly one request can succeed and the rest get a clean rejection rather than a silent overbooking.
Schema and queries
- PostgreSQL schema for venues, games, players and bookings
- Indexes tuned for the one query that runs constantly — open games near a location, ordered by start time
- Booking history kept as events, so a cancellation is a record rather than a deletion