async

SQLAlchemy 2.0 from the production angle. The engine/session/transaction layering, the typed declarative, the identity map, the N+1 query problem, async-only gotchas (no lazy loading), savepoint nesting, and the connection-pool knobs that decide whether the backend survives load.

Async Python from the bytecode up. Coroutines vs return values, how the event loop schedules tasks, when async beats threading or multiprocessing, structured concurrency with TaskGroup, and the cancellation rules that production backends live or die by.

Learn how message queues and pub/sub decouple services, why at-least-once delivery demands idempotent consumers, how backpressure and dead-letter queues protect the system, and when microservices are worth the complexity — with a sequenceDiagram of async order processing.

Threads are not the only model for concurrency. Learn how blocking vs non-blocking I/O works, how the event loop and reactor pattern scale to millions of connections, and how callbacks evolved into futures, promises, and async/await — plus where coroutines fit and when async loses to threads.

How Node 22 actually runs your code: V8, the libuv event loop and its phases, microtasks vs macrotasks, blocking pitfalls, and where worker threads, npm, pnpm, and bun fit in 2026.

Commands tell, events announce. How event-driven systems decouple producers from consumers, when CQRS and event sourcing earn their complexity, and the eventual-consistency tax you pay either way.

Async work between services without one tripping the other. Point-to-point vs pub/sub, the three delivery guarantees and what they cost, dead letter queues, and how to pick between Kafka, RabbitMQ, SQS, and friends.