L09 Synchronization and Fan-In/Fan-Out Behavior

Metadata

• Lecture ID: L09
• Track: E (Resource and Synchronization)
• Tier: 2-3
• Duration: 20 minutes
• Prerequisites: L03, L04

Learning Objectives

1. Explain multi-rate coordination with edge adapters.
2. Understand fan-out sampling and fan-in aggregation behavior.
3. Diagnose dropped-frame/backpressure signals in runtime logs.

Core Concept

• Mental model: sampling semantics are edge-level decisions, not node-level guesses.
• Key pitfall: assuming downstream rates automatically preserve all upstream events.

Live Demo Mapping

• Primary runnable file: examples/tutorial/e_resource_and_sync/01_multirate_window.py
• Optional extension: examples/tutorial/e_resource_and_sync/02_synchronization.py

Runnable Commands

Run from repository root:

pixi run python -m examples.tutorial.e_resource_and_sync.01_multirate_window --backend multiprocessing --duration 2

Optional fan-in sync demo:

pixi run python -m examples.tutorial.e_resource_and_sync.02_synchronization

What To Observe

• 30Hz source + 10Hz smoother + 1Hz printer behavior is visible in output cadence.
• Window(..., agg="mean") stabilizes downstream signal.
• Runtime warnings indicate queue pressure and sampling tradeoffs.

Failure Drill

• Reduce buffer/window settings and observe increased dropped-frame warnings.

Exercise

• Required: tune duration/window and explain trend smoothness changes.
• Stretch: compare Window behavior with a Latest-only edge in the same topology.

Evaluation Rubric

• Pass: learner can explain where fan-in/out behavior is defined in the graph.
• Failure signature: learner cannot relate queue warnings to adapter/rate decisions.

Follow-up

• Next lecture: l10_stateful_flows_and_reset_contracts.md