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This is a medium difficulty System Design question, commonly asked during Technical Screen rounds at Roblox.

What role is this question designed for?

This question is commonly asked for Software Engineer candidates at Roblox during technical interviews.

Design in-game payment wallet system

Last updated: Mar 29, 2026

Quick Overview

This question evaluates a candidate's ability to design a scalable, low-latency in-game currency subsystem covering transfer semantics, double-spend prevention, data modeling, APIs, and near real-time plus historical analytics.

Roblox

Jul 29, 2025, 8:05 AM

Software Engineer

Technical Screen

System Design

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:

Near real‑time analytics for inflow/outflow totals over the past 24 hours for any account.
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

Enable transfers of in‑game currency between accounts.
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.

Solution

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