Performance Interview Questions

24 real Performance questions asked in live technical interviews — each with a model answer. Updated weekly.

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Using the Parquet file format, queries are fast. What optimizations are done using Parquet?🟢 Easy · Conceptual · Asked 3×Suppose the MCPC server normally spawns in 300 milliseconds, but suddenly a request takes more than 10 seconds. The database and other backends appear healthy. How would you investigate this?🟡 Medium · Debugging · Asked 1×You mentioned using the Spark UI to identify slow stages and adjust parallelism. How would you ensure ACID transactions, schema evolution, and good query performance in your Spark workloads?🟡 Medium · Conceptual · Asked 1×How would you identify bottlenecks and optimize Spark performance? Can you walk me through your approach?🟡 Medium · Conceptual · Asked 1×If one executor is taking 90% of the execution time while the rest handle only 10%, how would you handle this imbalance?🟡 Medium · Conceptual · Asked 1×Have you written any SQL procedures? How would you ensure that your PL/SQL procedure processes financial data remains performant during migration to Python or vice versa?🟡 Medium · Conceptual · Asked 1×Why are wide transformations costly?🟡 Medium · Conceptual · Asked 1×How can a slow query be optimized to fetch results fast?🟡 Medium · Conceptual · Asked 1×How do you handle performance when processing a large number of records?🟡 Medium · Conceptual · Asked 1×Let's say we are doing data backup on S3 storage and it's taking a lot of time. How would you mitigate this issue? What approaches would you have?🟡 Medium · Conceptual · Asked 1×Scenario: we have a massive sales table and a smaller product table. The join is taking too long. What would you do?🟡 Medium · Debugging · Asked 1×Let's say the data is stored on a host server and is a little large. Will that pose any issue if we expose it via a REST API? If so, what solution would you propose?🟡 Medium · Conceptual · Asked 1×What specific indexes would you create for an optimized version to support those joins and filters?🟡 Medium · Conceptual · Asked 1×Can you tell how to optimize Spark jobs for streaming data?🟡 Medium · Conceptual · Asked 1×If we have a huge table in Amazon Redshift, what options would you consider to optimize its performance?🟡 Medium · Conceptual · Asked 1×The table is queried by ID, but the ID is modified frequently.🟡 Medium · Conceptual · Asked 1×We are processing a 1PB dataset on an MR cluster. The job is a join between a large sales dataset and a medium‑sized stores dataset. The job consistently crashes without a memory issue. Why do you think the executioner is failing?🔴 Hard · Debugging · Asked 1×A pipeline ingests data into an ISO table every hour. Over six months, query performance has dropped and S3 storage cost has spiked due to millions of tiny metadata files. What approach would reduce cost and improve pipeline performance?🔴 Hard · System Design · Asked 1×Suppose a query was running, and suddenly it starts taking a long time to execute. What could have gone wrong with the query source?🟡 Medium · Debugging · Asked 1×Why is Spark faster than normal Python computations?🟡 Medium · Conceptual · Asked 1×Why do we need to take timing into account?🟢 Easy · Conceptual · Asked 1×If we are going to display 10,000 records at a time, what would we do?🟡 Medium · Conceptual · Asked 1×How can you efficiently grow a particular grid in a React application?🟡 Medium · Conceptual · Asked 1×Suppose you need to display under 10,000 rows efficiently; what ways can you achieve this?🟡 Medium · Conceptual · Asked 1×

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