MongoDB and Redis arrived in 2009 promising escape from SQL's rigid schemas. Web 2.0 companies drowning in data grabbed the lifeline. No more schema migrations. No more JOIN complexity. Just store JSON and scale horizontally forever.
Fifteen years later, those organizations are hiring specialized teams to manage what SQL handled automatically. The "schemaless" databases still have schemas—they're just scattered across application code, enforced inconsistently, and invisible to query optimizers. What looked like operational simplicity became expertise overhead that compounds with every new developer onboarded.
The market tells the story SQL's defenders couldn't. Despite aggressive adoption campaigns and venture capital tailwinds, NoSQL holds 3% of database revenue. Most organizations either returned to SQL or adopted NewSQL hybrids like Spanner that learned the lesson: you can't eliminate complexity, only relocate it. The question isn't whether your data has structure. It's whether that structure lives in your database or your debugging sessions.