Company: Cisco

Difficulty: hard

Problem Statement

Distributed Trace Clock-Skew Reconciler A payments platform has just survived a multi-hour outage and the forensics team is reconstructing what happened. The evidence is a pile of logs pulled from `M` microservice hosts. Each host stamps its log lines with its own local clock, and every one of those clocks runs at a fixed, unknown offset from the others. Until the offsets are pinned down, the logs cannot be merged into a single timeline. The distributed tracing system emits **calibration records**. When a traced request crosses from host `a` to host `b`, the tracer measures the hop and reports the exact difference between the two hosts' clock readings for that instant. Each such record asserts a hard fact of the form "host `b`'s clock reads exactly `d` microseconds ahead of host `a`'s clock", where `d` may be negative. Chaining these facts propagates knowledge: once `a` and `b` are related and `b` and `c` are related, the offset between `a` and `c` is fully det

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