System design interview question
"Design a distributed unique ID generator. IDs must be unique across a fleet of thousands of machines, must be roughly sortable by creation time, and should be compact — 64 bits, not 128. Millions of IDs per second, and generation must not require coordination on every call."
bit-level design under hard constraints, plus the failure modes that break naive implementations — clock skew, clock rewind, and machine-ID assignment. It is a compact question with exactly one good answer shape, and the signal is whether the candidate derives the bit allocation rather than reciting it.
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