Exactly-once, on a connection you do not control
A pharmacy till has to keep selling when the internet drops, then reconcile without recording a sale twice. That constraint decides the whole architecture.
tail -f ~/notes
Writing
Concepts from the proof, explained in my own words with code from my own systems.
Syncing a catalogue you do not own
Tens of thousands of products from a third-party supplier, continuously synchronised. The bugs here are not in the fetch, they are in the clock.
The database was the bottleneck: 6s to 2s on a live marketplace
A production marketplace responding in six seconds. The instinct is to suspect the sockets or add a server. Profiling said the database, and the fix cost nothing to run.
Escrow is not a boolean
Holding money between two parties looks like a status field. It is a balance, a state machine, and a transaction boundary you have to draw narrowly on purpose.
Inheriting a codebase you did not write, and migrating it anyway
Eighteen models in TypeScript over SQL, handed over to be moved to a new stack. The rewrite came out with sixteen, which is the number that mattered.
Schema as data: what a no-code CMS actually costs
Letting clients define their own content types means storing schemas as data. That buys instant onboarding and hands back things the database used to do for you.
Proximity is a database problem, not an application problem
What is near me is the query a discovery platform lives on. Where you compute it decides whether the product still works once the catalogue is worth having.