durable-objects

Extend the DurableObject class from cloudflare:workers and configure new_sqlite_classes in your wrangler migrations. Initialize tables inside the constructor using ctx.blockConcurrencyWhile with ctx.storage.sql.exec for synchronous SQL operations.

Use @cloudflare/vitest-pool-workers with defineWorkersConfig pointing at your wrangler config. Access stubs via env from cloudflare:test, inspect internals with runInDurableObject, and trigger alarms immediately with runDurableObjectAlarm.

Use Durable Objects for coordination, strong consistency, per-entity storage, persistent WebSocket connections, and per-entity scheduled work. Use plain Workers for stateless request handling, maximum global distribution, or high fan-out independent requests.

No, PRAGMA user_version is not supported in Durable Objects SQLite storage. Track schema versions in a dedicated _sql_schema_migrations table and apply incremental migrations during constructor initialization.

blockConcurrencyWhile blocks all concurrency in the instance, so using it on every request caps throughput at roughly 200 requests per second. Reserve it for one-time initialization and never hold it across fetch calls or external I/O.

Each DO supports one alarm at a time, and calling setAlarm replaces any existing alarm. The alarm handler runs with automatic retries on failure, so handlers should be idempotent and can reschedule by calling setAlarm again.