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A handbook for software systems

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Client retry with key. Deduplication lock. Cached response.KEY VALIDATION · STATE LOCK · EXACTLY-ONCECLIENT REQPOST /chargeKey: ik_982RETRY (TIMEOUT)POST /chargeKey: ik_982DEDUP STOREik_982: LOCKEDTTL: 86400s · cachedEXECUTIONOrder #402Mutated OnceDuplicate Detected → Return Cached 200 OKSkips second mutation · prevents double billing1 mutation + N retries = exactly 1 state change
FIG. 01 — EXACTLY-ONCE MUTATION SEMANTICS
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★ Featured ConceptFeatured concept

Monotonic fencing tokens defeating split-brain writes

Prevent silent data corruption when long GC pauses or network partitions expire leases before storage writes complete.

Trace fencing tokens
CONCEPT ARCHITECTURE FLOW
AcquireToken 34
GC PauseLease Lost
StorageReject Stale

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