Design in-game payment wallet system
System Design: In‑Game Currency Transfers and Analytics
Context
You are designing the in‑game currency subsystem for an online game. Players can transfer currency between accounts. Product and ops need:
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Near real‑time analytics for inflow/outflow totals over the past 24 hours for any account.
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An hourly balance time series for the past 30 days for any account.
Assume a single in‑game currency, high read volume, and strict prevention of double‑spending. All timestamps are UTC.
Requirements
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Enable transfers of in‑game currency between accounts.
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Provide APIs and data models to:
a) Query any account’s total inflow and outflow over the past 24 hours.
b) Retrieve an hourly balance time series for the past 30 days for any account.
Deliver data models, APIs, and any supporting components necessary to meet these requirements with low latency and correctness.
Constraints & Assumptions
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Preserve the scope, facts, inputs, and requested outputs from the prompt above.
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If the prompt leaves a detail unspecified, state a reasonable assumption before relying on it.
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Keep the answer interview-ready: concise enough to present, but concrete enough to implement or evaluate.
Clarifying Questions to Ask
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Clarify users, core use cases, read/write patterns, scale, latency, availability, and data retention.
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State explicit assumptions before making sizing or architecture decisions.
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Prioritize the functional path first, then address reliability, security, observability, and rollout.
What a Strong Answer Covers
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A scoped requirements summary with concrete non-goals and success metrics.
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API, data model, architecture, consistency, capacity, and operations.
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Reasoned trade-offs among simple and scalable designs, including bottlenecks and failure modes.
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A validation, monitoring, migration, and launch plan appropriate for the risk level.
Follow-up Questions
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What breaks first at 10x traffic or data volume?
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How would you degrade gracefully during dependency failures?
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What metrics and alerts would prove the design is healthy after launch?