PayU Payments Senior Software Engineer Interview Questions and Answers

Implement thread safe load balancer.
focus on input validations and cover all corner cases in tests

Q1. Low Level Design: How to do rate limiting for a platform serving 100K requests per second.
Ans. 
Implement rate limiting for a platform serving 100K requests per second.
• Use a token bucket algorithm to limit the rate of incoming requests.

• Set a maximum number of tokens in the bucket to control the rate.

• Refill the bucket at a constant rate to allow bursts of requests.

• Track the timestamp of the last request to enforce the rate limit.

• Consider using a distributed rate limiting system for scalability.

• Monitor and adjust t...read more
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Q1. Explain Concurrency
Ans. 
Concurrency is the ability of a system to execute multiple tasks simultaneously.
• Concurrency allows multiple tasks to run concurrently, improving performance and efficiency.

• Concurrency can be achieved through multithreading or multiprocessing.

• Example: A web server handling multiple requests simultaneously using multithreading.
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Q2. Explain Acid principles
Ans. 
ACID principles are a set of properties that guarantee database transactions are processed reliably.
• Atomicity: Transactions are all or nothing. If one part of the transaction fails, the entire transaction is rolled back.

• Consistency: Transactions bring the database from one valid state to another. All constraints are satisfied.

• Isolation: Transactions are isolated from each other until they are completed.

• Durability: Once...read more
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Q1. Current company architecture and what was your role
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Q1. Detailed flow from FE to BE to db.
Ans. 
The flow of data from the front end to the back end to the database.
• Front end sends a request to the back end server.

• Back end processes the request and interacts with the database.

• Database retrieves or updates the data and sends it back to the back end.

• Back end sends the response to the front end for display.
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Q1. How to pass input field values from form to db. How to make code testable/loosely coupled.
Ans. 
Pass input field values from form to db by using a data access layer and dependency injection for testability.
• Create a data access layer to handle interactions with the database.

• Use parameterized queries to prevent SQL injection.

• Implement dependency injection to decouple the code and make it testable.

• Mock the data access layer in unit tests to isolate database interactions.

• Use interfaces to define contracts between com
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Q1. Salary discussion
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Q1. They asked about previous projects in depth
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Q1. They asked techinal all java
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Q1. Techincal kafka all questions
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Interview was conducted by third party for screening
Basic GoLang question
Basic question on Kubern8s cluster
Question on aggregating different Strings based on requirement.