Idempotency
An operation that produces the same result whether you run it once or multiple times. Critical for safe retries in distributed systems.
What is Idempotency?
An operation that produces the same result whether you run it once or multiple times. Critical for safe retries in distributed systems.
Idempotency is a foundational concept that sits in the Core Fundamentals area of system design. Engineers reach for it whenever they need to reason about real-world trade-offs in that space — not just for textbook correctness, but because real production systems at companies like Netflix, Amazon, and Google make these decisions every day.
If you want to go deeper than this definition — with diagrams, code, and a quiz to lock it in — work through the "Idempotency" lesson linked below. It walks through the why, the mechanism, the trade-offs, and how the giants actually use it in production.
Learn Idempotency in depth
Full interactive lesson with diagrams, code examples, real-world references, and a quiz.
Open the Idempotency lessonRelated lessons
Lessons that touch on Idempotency as part of a larger topic.
Idempotency Keys
Safely retry failed API requests without causing duplicate side effects
intermediate · api design protocols
Design a Payment System
Design a payment processing system - ACID transactions, idempotency, reconciliation, retry strategies, and the saga pattern for distributed payments
capstone · capstone
Message Deduplication
Detect and discard duplicate messages before they cause double-processing
intermediate · messaging event systems
Idempotent Consumer
Design consumers that produce the same result whether a message is processed once or ten times
intermediate · messaging event systems
Exactly-Once Delivery
The holy grail of messaging, process every message once and only once. Here's why it's nearly impossible and how to fake it.
intermediate · messaging event systems
See also
Related glossary terms you might want to look up next.
REST API
An architectural style for building APIs using standard HTTP methods (GET, POST, PUT, DELETE). Resources are identified by URLs.
Retry
Automatically re-attempting a failed operation, usually with exponential backoff. Essential for handling transient failures in distributed systems.
HTTP
The protocol powering the web. A request-response model where clients ask for resources and servers respond. Stateless by design.