Nielsen

Role: Data Engineer

College: Not Specified

Interview Date: September 2024

Interview Type: Off-Campus

Result: Selected

Difficulty: Medium-Hard

Rounds: 3 rounds

Topics Asked: SQL, PySpark, Python, Scenario-based questions, Spark Optimizations (AQE, data skewness), Project-related, Behavioral

Experience:

This Data Engineer interview experience at Nielsen (and Visa) was shared on Reddit in September 2024 by a candidate who applied on the company's website.

Round 1: SQL, PySpark, and Scenario-Based Questions

This round included SQL queries, PySpark coding questions, and scenario-based problems.

• **PySpark coding questions:** Examples included finding the first letters of words and their word count.
• **Scenario-based PySpark:** "We have cached a dataframe but when we are trying to write again multiple jobs are running. Why?"
• **SQL/PySpark/Python problem:** "There is a table of cricket teams, you need to find match fixtures (each team will play exactly once with each other). Solve this in SQL, PySpark, and Python (in this case a list of teams are given instead of table)."
• **Scenario-based data processing:** "There is a log txt file which has IP addresses of websites called, you need to find the top 5 most visited websites."
• **Large file update scenario:** "There is a large file of size petabyte at a path, and we received another file which contains new record and old updated records. How to update the file with new records and update data at the location."
• **Spark Optimization theory:** Questions on AQE (Adaptive Query Execution), data skewness.
• **Data Management:** "How do you maintain the history of changes for a particular table."

Round 2: Technical Round

This round likely delved deeper into the technical aspects, possibly expanding on the topics from Round 1 or introducing new ones relevant to data engineering. While not explicitly detailed as a separate snippet, the overall experience indicates a strong technical focus.

Round 3: Managerial Round and Project-Related Questions

This round focused on managerial aspects and projects. A behavioral question was asked: "What would you do when asked to take up a new task when you don't have any bandwidth?"

The candidate was selected for the role.