How do I approach System Design interview questions?

System Design questions require understanding of core concepts and practice. PracHub provides solutions with explanations to help you master system design interviews.

What difficulty level is this interview question?

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

What role is this question designed for?

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

Design Points-from-Transactions Service

Quick Overview

This question evaluates system design and distributed-systems competency, focusing on transaction processing, idempotency and deduplication, monetary precision and rounding, consistency models, data modeling, and operational controls like observability and fraud prevention.

Design a Scalable Loyalty Points Service (USD → Points at 1 USD = 1.5 Points)

You are designing a service that awards loyalty points for purchase transactions denominated in USD at a fixed conversion rate of 1 USD = 1.5 points. The service must support awarding, querying balances, and redeeming points at scale, with correctness and auditability.

Assume transactions arrive from a card/payments platform and that points should be awarded only for posted/settled transactions (not authorizations). Redemption must prevent double-spend.

Cover the following:

API Design
- Ingest transactions for awarding points
- Query balances
- Redeem points
Idempotency and Deduplication
- How to ensure exactly-once awarding and idempotent client retries
Precision and Rounding
- Units to store money and points, conversion math, rounding policy
Consistency Model
- What is strong vs. eventual, and where to apply each
Data Model and Schema
- Tables, keys, indices, constraints, and how balances are computed
Prevention of Double Counting and Fraud
- Controls for duplicate events, replay, redemptions, and abuse
Real-time and Batch Processing
- Streaming path for new transactions and batch backfills
Backfill and Correction Flows
- Handling refunds, chargebacks, retroactive fixes, and rate changes
Scaling and Partitioning Strategy
- Per-account ordering, sharding, and throughput considerations
Observability
- Metrics, logs, tracing, and audits to ensure correctness and SLAs
Rollout and Testing Plans
- Validation, shadowing, canaries, and guardrails

Quick Overview

Design a Scalable Loyalty Points Service (USD → Points at 1 USD = 1.5 Points)

Assume transactions arrive from a card/payments platform and that points should be awarded only for posted/settled transactions (not authorizations). Redemption must prevent double-spend.

Cover the following:

API Design

Ingest transactions for awarding points
Query balances
Redeem points

Idempotency and Deduplication

How to ensure exactly-once awarding and idempotent client retries

Precision and Rounding

Units to store money and points, conversion math, rounding policy

Consistency Model

What is strong vs. eventual, and where to apply each

Data Model and Schema

Tables, keys, indices, constraints, and how balances are computed

Prevention of Double Counting and Fraud

Controls for duplicate events, replay, redemptions, and abuse

Real-time and Batch Processing

Streaming path for new transactions and batch backfills

Backfill and Correction Flows

Handling refunds, chargebacks, retroactive fixes, and rate changes

Scaling and Partitioning Strategy

Per-account ordering, sharding, and throughput considerations

Observability

Metrics, logs, tracing, and audits to ensure correctness and SLAs

Rollout and Testing Plans

Validation, shadowing, canaries, and guardrails

Design Points-from-Transactions Service

Quick Overview

Design a Scalable Loyalty Points Service (USD → Points at 1 USD = 1.5 Points)

Solution

Submit Your Answer to Earn 20XP

Design Points-from-Transactions Service

Quick Overview

Design a Scalable Loyalty Points Service (USD → Points at 1 USD = 1.5 Points)

Solution

Submit Your Answer to Earn 20XP