Book: Database Playbook My project: Hermes IDE | GitHub — an IDE for developers who ship with Claude Code and other AI coding tools Me: xgabriel.com | GitHub Picture the IoT telemetry team that spends weeks moving multi-TB workloads from MongoDB to ClickHouse, watches a Grafana dashboard drop from 14 seconds to under 200 ms on an hourly aggregate, and confirms the migration was the right call. (Numbers illustrative; the shape of the win is the common one.) Picture the other team, the one that moved customer profile data from Postgres to MongoDB after reading a blog post about "schema flexibility," and discovered every customer-facing query now needed two round-trips and a manual join in application code. An engineer I know rolled that exact migration back. The bill was paid in developer-weeks and one Friday-night incident. The difference between those stories isn't which database is "better." It's whether the team asked the five questions below first.…