durable-objects

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

Use @cloudflare/vitest-pool-workers to run tests inside the Workers runtime. 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, and persistent WebSocket connections. Use plain Workers for stateless request handling, maximum global distribution, and high fan-out independent requests.

blockConcurrencyWhile blocks all concurrency, so using it on every request limits throughput to roughly 200 requests per second. Reserve it for one-time constructor initialization and never hold it across fetch or external I/O.

No, PRAGMA user_version is not supported in Durable Objects SQLite storage. Track schema versions with a dedicated _sql_schema_migrations table, or use libraries like durable-utils that provide a SQLSchemaMigrations class.

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