Nubank Senior Software Engineer Interview Experience — Chargeback Ingestion and a Database Read Bottleneck

Problem: Design a Chargeback Ingestion System

Design a system that processes card chargeback/dispute transactions.

The system receives chargeback-related transaction events, validates and deduplicates them, tracks their processing state, persists them, and eventually exports eligible transactions into CSV files. These CSV files must be sent to Mastercard via FTP/SFTP.

The difficulty felt all right. I failed mainly because there was a database-read bottleneck that I didn't recognize at the time. Batched reading would actually have solved it. The interview experience was all right.