On-callHardoc-g228

Subject Hot partitionLevel Senior–Staff~35 minCommon in Distributed systems interviewsIndustries Technology, Software development

Question

DynamoDB table keyed on `streamId` (partition key) + `ts` (sort key) storing live-stream chat events. During a single huge livestream, the app starts getting `ProvisionedThroughputExceededException` / throttling on writes for that stream while overall table-level consumed capacity is well under the provisioned total. CloudWatch shows one partition's throttle count spiking; everything else is fine. The stream has 5M concurrent viewers chatting. Triage, mitigate live, and redesign so it can't recur.

What a strong answer looks like

Stop the bleeding first (mitigate), then form hypotheses from real signals. Separate root cause from symptom, communicate status as you go, and close with what prevents a repeat.

Learn the concepts

Diagram & narrate the incident

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Run or narrate your approach, then ask the coach.