Engineering | Gradient

The Spring Boot race condition that sells your last unit twice

October 6, 2026 by Nabeel Ahmed

Spring Boot race condition in a @Transactional checkout method: the stock read, the check and the write-back are highlighted as three separate steps

Two requests read “1 left”, both pass the check, both commit. Why @Transactional does not stop it, a test that proves it every time, and three fixes compared.

Hikari connection is not available? Your REQUIRES_NEW is starving the pool

October 6, 2026 by Nabeel Ahmed

Hikari connection is not available: an audit service marked REQUIRES_NEW, which needs a second pooled connection when a @Transactional checkout calls it

Each checkout holds one pooled connection and waits for a second. Why REQUIRES_NEW starves HikariCP under load, a test that proves it, and three fixes compared.