Blog

Command Semantics over MQTT

The hardest problem in device communication over MQTT is not delivery. It is semantic consistency under concurrency. Once you scale beyond a single service instance and a single stable device connection, three things become unavoidable: Messages are duplicated; they arrive late; state transitions race.

Most designs fail not because MQTT misbehaves, but because command progression is modeled implicitly instead of...

Why Cannot Close a Go Channel Twice

Every time someone asks why closing a channel twice panics, the real question is usually about ownership.

PostgreSQL Locks & Spring JPA Locks

I recently spent some focused time reading PostgreSQL’s concurrency and locking documentation, and then mapping that understanding to how locks actually work in Spring JPA / Hibernate.

This is not a reference manual.
It’s a mental model — the kind that helps avoid race conditions, deadlocks, and subtle production bugs. (with the help with AI)