DELETE Doesn’t Delete Data: Understanding DELETE, VACUUM, and Time Travel in Delta Lake

I spent the first 8 years of my career in domains full of sensitive PII, PHI, and HIPAA regulations. In 2026 I was brought into a Xorbix team that had been deliberate in its AI adoption for years before my arrival.  As I’ve worked to catch up with the rest of the team, some of the clearest lessons have come from our Pull Request (PR) review process.