Inside Hyperdrive: How we solved a rare Hyperdrive MySQL caching bug

Hyperdrive support for MySQL is now generally available (GA). Hyperdrive, Cloudflare’s database connection pooler for Workers, initially only supported Postgres. Since we announced the beta for MySQL protocol support last year, we have been working on making our MySQL handling as reliable as our Postgres support. We’ve learned some things from building and running a MySQL connection pooler on Cloudflare’s network. It turns out that the difference between beta and GA is just 20 bug fixes in a trenchcoat. During the beta, our goal was to validate that real-world customer usage hit our production availability target of 99.99%. We knew there were gaps in our reliability since we track how often client connections from a Worker end in an error related to Hyperdrive. In addition, we had feedback from customers in the beta that led to the discovery of a rare and subtle bug in our production environment. To convey the complexity of this particular bug, we first need to explain how Hyperdrive works. What is Hyperdrive? Hyperdrive is a distributed database connection pooler that connects Cloudflare Workers to SQL databases. Hyperdrive holds warm SQL connections open on our…