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Idempotency as Reliability Foundation

Operations that produce the same result regardless of how many times they execute enable safe retries, which is essential for reliability over unreliable networks where "at-least-once" delivery is easier than "exactly-once."

Tension Addressed

Stability vs. Evolution

Recognizable As

PUT semantics (replace entire resource), DELETE semantics (remove if exists), idempotency keys for POST operations, retry-safe operations, "upsert" patterns

Canonical Sources

HTTP/1.1 RFC 7231 (method properties); Helland, "Building on Quicksand" (2009); Kleppmann, "Designing Data-Intensive Applications" (2017)

Transfers To

Distributed systems (exactly-once semantics), Message queues (deduplication), Database operations (upserts), Functional programming (referential transparency)

Idempotency is not just an HTTP concept - it's a fundamental property for building reliable systems. When networks fail mid-request, the only safe retry strategy is one where repetition causes no harm.

Sub-concepts: - Idempotency keys: Client-generated identifiers that allow non-naturally-idempotent operations (like payments) to be safely retried - Natural vs. artificial idempotency: Some operations are inherently idempotent (set value to X); others require explicit deduplication mechanisms