Cognizant
American multinational information technology services and consulting company.
4 Rounds
~21 Days
Medium
The Interview Loop
Recruiter Screen (30 min)
Standard fit check, behavioral questions, and resume overview.
Technical Loop (3-4 Rounds)
Deep dive into domain knowledge, coding, and system design.
Interview Question Bank
Data Engineer
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Coding
•
medium
Write a PySpark script to read a CSV file from S3, drop rows with null values in a specific column, group by another column to find the average, and write the output back to S3 as Parquet.
#DataFrames
#I/O
#Aggregations
Data Engineer
•
Coding
•
medium
Write a PySpark DataFrame query to pivot a table. You have columns: 'Store', 'Month', and 'Revenue'. Pivot the 'Month' column so each month is a separate column showing the revenue.
#Pivot
#Data Aggregation
Data Engineer
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Technical
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hard
How do you handle data skewness in PySpark? Walk me through the exact steps you would take if a join operation is taking too long due to a skewed key.
#Performance Tuning
#Data Skew
#Salting
#Broadcast Join
Data Engineer
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Technical
•
easy
What is the difference between a narrow and wide transformation in Spark? Give examples of each.
#Spark Architecture
#Transformations
#Shuffling
Data Engineer
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Technical
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hard
You have a PySpark job failing with an OutOfMemory (OOM) error on the executor side. What are the potential causes and how do you troubleshoot it?
#Troubleshooting
#Memory Management
#OOM
Data Engineer
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Technical
•
medium
What is the difference between repartition() and coalesce() in PySpark? When would you use one over the other?
#Partitioning
#Performance Tuning
Data Engineer
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Technical
•
medium
How does Spark handle fault tolerance? Explain the role of the DAG and RDD lineage.
#Fault Tolerance
#Lineage
#DAG
Data Engineer
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Technical
•
medium
What are User Defined Functions (UDFs) in PySpark? Why are Python UDFs generally discouraged, and what is the alternative?
#UDFs
#Performance Tuning
#Pandas UDFs
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Senior EngineerFocuses on core competencies, system constraints, and clear communication.
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Always explain your thought process before writing code or drawing architecture.