Vitess

Vitess is how YouTube scaled MySQL to handle billions of queries. It's a database clustering system that adds horizontal sharding, connection pooling, and query routing to MySQL without changing your application code. Battle-tested at Google-scale.

If your MySQL database is hitting performance limits and you're considering a rewrite to a distributed database, Vitess lets you keep MySQL and scale it horizontally. PlanetScale is literally built on Vitess (hosted, managed, easier). CockroachDB offers similar horizontal scaling but with Postgres compatibility. TiDB is another MySQL-compatible distributed database with less operational complexity.

Best for teams with existing MySQL apps that need to scale beyond a single server without rewriting queries. This is infrastructure-team territory, not solo-founder territory.

The catch: operating Vitess is a full-time job. The learning curve is steep — topology servers, vtgate, vttablet, and sharding schemes all need understanding. If you're not already at MySQL's scaling limits, you're adding complexity for no reason. PlanetScale exists precisely because running Vitess yourself is hard.