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MediumAI MLSystem design
Two replicas each serve30 requests/minute. Arrivals rise to 90. A third replica takes three minutes to become ready; nothing expires or is rejected. Calculate backlog at readiness and whether it drains. What if a fourth is ready then?
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2Answer out loud, not in your head
3Then compare with the answer below
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How would you distinguish a tokenizer bottleneck from exhausted GPU capacity?
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- A 24 GiB GPU holds13 GiB of weights and reserves3 GiB for runtime. Standard non-MLA attention has 32 layers,8 KV heads,128 head dimension and 2-byte cache values. Every request may hold8,192 input-plus-output tokens. Calculate the simplified concurrency bound and explain why a test at twelve concurrent requests can fail.
- The same mixed chat/document trace produces 900 output tokens/s with chat p95 gaps 35 ms. A larger batch produces 1,080 tokens/s but chat gaps 70 ms. The chat limit is 50 ms. Decide whether to accept and propose a controlled next test.
- Eight GPUs are available on four hosts, two per host. The model requires two GPUs per replica. A host-local replica measures40 requests/minute; an eight-GPU group measures110. Demand is 100/minute after one host loss. Compare the two layouts under the assumption that a parallel replica needs every worker.
- In matched one-hour measurement runs, configuration A costs 12 units/hour and serves 18,000 completed responses, of which 3,000 are late. Configuration B costs 10 units/hour and serves 12,000 timely responses. No other failures occur. Which is cheaper per thousand timely successes, and what does that comparison omit?
- A shared pool has 12,000 free reserved tokens; tenant T has 4,000 under its active limit. A request needs 6,000 and expires in one second; no release is expected for three seconds. What should admission do, and how should a retry reuse identity?
- Account A starts at 100 units before this batch. Each accepted event adds its signed delta; these are not full balance snapshots. Durable event identity is (source, event_id), and the first valid accepted payload is immutable. An exact retry has no new effect. A later different payload with the same identity is quarantined and does not replace the accepted event. Corrections must be new authorized events with their own identity and a reference to the original event. All rows below target A and the correction is authorized. Process them in the stated delivery order.