Emeka Nwosu

Our reconciliation job was wrong every day for a week because London changed its clocks

Story from March that I promised a few people. Clocks go back again on the 25th, so this is the right week. I work from Enugu for a London fintech. Nigeria is UTC+1 all year, no daylight saving. London is UTC+0 in winter and UTC+1 in summer. Our partner bank sends a settlement file per "London business day", midnight to midnight London time. Our reconciliation job builds the same window on our side and matches…

Sending this to every PM who asks why we picked Go. 100 seconds, no generics debate, no borrow checker, just goroutines. Fireship explains it better than my last architecture doc 😂

rust is a language for people who enjoy suffering. go is a language for people who enjoy shipping. NEPA took light twice today, inverter beeped like a smoke alarm, service still up. gophers rise 😂

Idempotency keys in Go: the version that survives a double tap and a dead inverter

Customer taps Pay. The request goes out on a 3G connection in Onitsha, reaches our API, the charge succeeds, and the response dies somewhere on the way back. The app sees a timeout and retries. Without protection, that is two charges and one very angry customer calling the merchant, who calls us. Same thing happens when NEPA takes light in the middle of a request and the client's inverter takes three seconds to kick…

Idempotent payment endpoints in Go and Postgres: the pattern that stopped our double charges

For six months we refunded somebody almost every Monday. Same story every time: customer on a bad connection taps Pay, the request reaches us, the PSP charges them, our response never reaches the phone, the app retries, we charge again. This is the pattern we use now. Zero double charges since February. The rules Every POST that moves money requires an Idempotency-Key header. No key, 400. The client generates it…