20 𝐫𝐞𝐚𝐥-𝐭𝐢𝐦𝐞 𝐬𝐜𝐞𝐧𝐚𝐫𝐢𝐨-𝐛𝐚𝐬𝐞𝐝 𝐢𝐧𝐭𝐞𝐫𝐯𝐢𝐞𝐰 𝐪𝐮𝐞𝐬𝐭𝐢𝐨𝐧𝐬

Here are few Interview questions that are often asked in PySpark interviews to evaluate if candidates have hands-on experience or not !!

𝐋𝐞𝐭𝐬 𝐝𝐢𝐯𝐢𝐝𝐞 𝐭𝐡𝐞 𝐪𝐮𝐞𝐬𝐭𝐢𝐨𝐧𝐬 𝐢𝐧 4 𝐩𝐚𝐫𝐭𝐬

1. Data Processing and Transformation
2. Performance Tuning and Optimization
3. Data Pipeline Development
4. Debugging and Error Handling

𝐃𝐚𝐭𝐚 𝐏𝐫𝐨𝐜𝐞𝐬𝐬𝐢𝐧𝐠 𝐚𝐧𝐝 𝐓𝐫𝐚𝐧𝐬𝐟𝐨𝐫𝐦𝐚𝐭𝐢𝐨𝐧:

1. Explain how you would handle large datasets in PySpark. How do you optimize a PySpark job for performance?
2. How would you join two large datasets (say 100GB each) in PySpark efficiently?
3. Given a dataset with millions of records, how would you identify and remove duplicate rows using PySpark?
4. You are given a DataFrame with nested JSON. How would you flatten the JSON structure in PySpark?
5. How do you handle missing or null values in a DataFrame? What strategies would you use in different scenarios?

𝐏𝐞𝐫𝐟𝐨𝐫𝐦𝐚𝐧𝐜𝐞 𝐓𝐮𝐧𝐢𝐧𝐠 𝐚𝐧𝐝 𝐎𝐩𝐭𝐢𝐦𝐢𝐳𝐚𝐭𝐢𝐨𝐧:

6. How do you debug and optimize PySpark jobs that are taking too long to complete?
7. Explain what a shuffle operation is in PySpark and how you can minimize its impact on performance.
8. Describe a situation where you had to handle data skew in PySpark. What steps did you take?
9. How do you handle and optimize PySpark jobs in a YARN cluster environment?
10. Explain the difference between repartition() and coalesce() in PySpark. When would you use each?

𝐃𝐚𝐭𝐚 𝐏𝐢𝐩𝐞𝐥𝐢𝐧𝐞 𝐃𝐞𝐯𝐞𝐥𝐨𝐩𝐦𝐞𝐧𝐭:

11. Describe how you would implement an ETL pipeline in PySpark for processing streaming data.
12. How do you ensure data consistency and fault tolerance in a PySpark job?
13. You need to aggregate data from multiple sources and save it as a partitioned Parquet file. How would you do this in PySpark?
14. How would you orchestrate and manage a complex PySpark job with multiple stages?
15. Explain how you would handle schema evolution in PySpark while reading and writing data.

𝐃𝐞𝐛𝐮𝐠𝐠𝐢𝐧𝐠 𝐚𝐧𝐝 𝐄𝐫𝐫𝐨𝐫 𝐇𝐚𝐧𝐝𝐥𝐢𝐧𝐠:

16. Have you encountered out-of-memory errors in PySpark? How did you resolve them?
17. What steps would you take if a PySpark job fails midway through execution? How do you recover from it?
18. You encounter a Spark task that fails repeatedly due to data corruption in one of the partitions. How would you handle this?
19. Explain a situation where you used custom UDFs (User Defined Functions) in PySpark. What challenges did you face, and how did you overcome them?
20. Have you had to debug a PySpark (Python + Apache Spark) job that was producing incorrect results?

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Tips to become a Data Engineer 👇👇

1. Data Engineering Basics: At its core, it's about efficiently moving and reshaping data from one place/format to another.
2. Be Curious: The field is vast. Dive deep, ask questions, and always be in the mode of learning and experimenting.
3. Master Data: Understand the intricacies of data types, where they originate, and how they're structured.
4. Programming: Grasping a language is crucial. If you're unsure, start with Python – it's versatile and widely used in the industry.
5. SQL: A timeless tool for querying databases. Mastering SQL will empower you to work with data across various platforms.
6. Command Line: Familiarizing yourself with command line operations can save a lot of time, especially for quick and repetitive tasks.
7. Know Computers: A basic understanding of how computers communicate and process information can guide better data engineering decisions.
8. Personal Projects: Practical experience is invaluable. Start projects, learn from them, and showcase your work on platforms like GitHub.
9. APIs and JSON: Many modern data sources are API-based. Understanding how to extract and manipulate JSON data will be a daily task.
10. Tools Mastery: Get proficient with your primary tools, but stay updated with emerging technologies and platforms.
11. Data Storage Basics: Know the difference and use-cases for Databases, Data Lakes, and Data Warehouses. Understand the distinction between OLTP (online transaction processing) and OLAP (online analytical processing).
12. Cloud Platforms: The cloud is the future. AWS, Azure, and GCP offer free tiers to start experimenting.
13. Business Acumen: A data engineer who understands business metrics and their implications can offer more value.
14. Data Grain: Dive deep into datasets to understand their finest level of detail. It aids in more precise querying and analytics.
15. Data Formats: Recognizing main data formats (like JSON, XML, CSV, SQLite, Database) will help you navigate different datasets with ease.

Kavitha's Journey to become a Data Engineer 👇👇

1. Startup to Dream Job Journey:
- Started at a startup in India, transitioned to Infosys, then grabbed UK opportunity.
- Shifted from legacy Mainframe to AWS Cloud, pursued Master's from illinoisstateu, and secured dream job at Statefarm.
2. Learn Fundamentals:
- Assess skills, understand role.
- Gain proficiency in Python, SQL.
- Learn data technologies.
3. Database and Modeling Skills:
- Understand databases, gain proficiency.
- Learn data modeling principles.
4. Master ETL, Warehousing, and Visualization:
- Understand ETL, data warehousing.
- Gain experience in building warehouses.
- Familiarize with visualization tools.
- Got Certified as AWS Solutions Architect.
5. Utilize LinkedIn for Job Search:
- Network and connect with professionals.
- Showcase skills and achievements.
- Utilize job search feature, leading to dream job at Statefarm.

Data Engineering Interview Preparation Resources: https://whatsapp.com/channel/0029Vaovs0ZKbYMKXvKRYi3C

Here's what the average data engineering interview looks like in 2025:

- 1 hour algorithms in Python
Here you will be asked irrelevant questions about dynamic programming, linked lists, and inverting trees

- 1 hour SQL
Here you will be asked niche questions about recursive CTEs that you've used once in your ten year career

- 1 hour data architecture
Here you will be asked about CAP theorem, lambda vs kappa, and a bunch of other things that ChatGPT probably could answer in a heartbeat

- 1 hour behavioral
Here you will be asked about how to play nicely with your coworkers. This is the most relevant interview in my opinion

- 1 hour project deep dive
Here you will be asked to make up a story about something you did or did not do in the past that was a technical marvel

- 4 hour take home assignment
Here you will be asked to build their entire data engineering stack from scratch over a weekend because why hire data engineers when you can submit them to tests?

DevOps Tech Stack

Data Engineering Tools:

Apache Hadoop 🗂️ – Distributed storage and processing for big data

Apache Spark ⚡ – Fast, in-memory processing for large datasets

Airflow 🦋 – Orchestrating complex data workflows

Kafka 🐦 – Real-time data streaming and messaging

ETL Tools (e.g., Talend, Fivetran) 🔄 – Extract, transform, and load data pipelines

dbt 🔧 – Data transformation and analytics engineering

Snowflake ❄️ – Cloud-based data warehousing

Google BigQuery 📊 – Managed data warehouse for big data analysis

Redshift 🔴 – Amazon’s scalable data warehouse

MongoDB Atlas 🌿 – Fully-managed NoSQL database service

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🔍 Mastering Spark: 20 Interview Questions Demystified!

1️⃣ MapReduce vs. Spark: Learn how Spark achieves 100x faster performance compared to MapReduce.
2️⃣ RDD vs. DataFrame: Unravel the key differences between RDD and DataFrame, and discover what makes DataFrame unique.
3️⃣ DataFrame vs. Datasets: Delve into the distinctions between DataFrame and Datasets in Spark.
4️⃣ RDD Operations: Explore the various RDD operations that power Spark.
5️⃣ Narrow vs. Wide Transformations: Understand the differences between narrow and wide transformations in Spark.
6️⃣ Shared Variables: Discover the shared variables that facilitate distributed computing in Spark.
7️⃣ Persist vs. Cache: Differentiate between the persist and cache functionalities in Spark.
8️⃣ Spark Checkpointing: Learn about Spark checkpointing and how it differs from persisting to disk.
9️⃣ SparkSession vs. SparkContext: Understand the roles of SparkSession and SparkContext in Spark applications.
🔟 spark-submit Parameters: Explore the parameters to specify in the spark-submit command.
1️⃣1️⃣ Cluster Managers in Spark: Familiarize yourself with the different types of cluster managers available in Spark.
1️⃣2️⃣ Deploy Modes: Learn about the deploy modes in Spark and their significance.
1️⃣3️⃣ Executor vs. Executor Core: Distinguish between executor and executor core in the Spark ecosystem.
1️⃣4️⃣ Shuffling Concept: Gain insights into the shuffling concept in Spark and its importance.
1️⃣5️⃣ Number of Stages in Spark Job: Understand how to decide the number of stages created in a Spark job.
1️⃣6️⃣ Spark Job Execution Internals: Get a peek into how Spark internally executes a program.
1️⃣7️⃣ Direct Output Storage: Explore the possibility of directly storing output without sending it back to the driver.
1️⃣8️⃣ Coalesce and Repartition: Learn about the applications of coalesce and repartition in Spark.
1️⃣9️⃣ Physical and Logical Plan Optimization: Uncover the optimization techniques employed in Spark's physical and logical plans.
2️⃣0️⃣ Treereduce and Treeaggregate: Discover why treereduce and treeaggregate are preferred over reduceByKey and aggregateByKey in certain scenarios.

Data Engineering Interview Preparation Resources: https://whatsapp.com/channel/0029Vaovs0ZKbYMKXvKRYi3C

𝗗𝗿𝗲𝗮𝗺 𝗝𝗼𝗯 𝗮𝘁 𝗚𝗼𝗼𝗴𝗹𝗲? 𝗧𝗵𝗲𝘀𝗲 𝟰 𝗙𝗥𝗘𝗘 𝗥𝗲𝘀𝗼𝘂𝗿𝗰𝗲𝘀 𝗪𝗶𝗹𝗹 𝗛𝗲𝗹𝗽 𝗬𝗼𝘂 𝗚𝗲𝘁 𝗧𝗵𝗲𝗿𝗲😍

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