Book: Database Playbook: Choosing the Right Store for Every System You Build My project: Hermes IDE | GitHub — an IDE for developers who ship with Claude Code and other AI coding tools Me: xgabriel.com | GitHub You're picking the primary store for a multi-tenant SaaS. Three product managers want a relational schema, one wants per-tenant flexibility, and the SRE has a 47-page deck arguing both sides at once. You have a Tuesday to decide. The argument never ends because the question is wrong. "MongoDB or Postgres" depends on the shape of the workload: write rate, schema volatility, query mix, consistency story. Pick the workload first, then the store falls out. Below is the decision table I keep handing engineers when they ask me which one to bet on, with the actual reasons each row goes the way it does.…