Visa Senior Data Scientist Interview Questions and Answers for Experienced

Q1. What are SSL certificates?
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SSL certificates are digital certificates that authenticate the identity of a website and encrypt information sent to the server.
• SSL certificates ensure secure communication between a user's browser and a website's server.

• They use encryption to protect sensitive data such as login credentials, credit card information, etc.

• SSL certificates are issued by Certificate Authorities (CAs) and contain information about the web...read more
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Q2. What are the ways to secure REST API?
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Securing REST API involves using authentication, authorization, encryption, and input validation.
• Use authentication methods like OAuth, JWT, or API keys to verify the identity of clients.

• Implement authorization to control access to resources based on user roles and permissions.

• Encrypt data transmission using HTTPS to protect sensitive information from being intercepted.

• Validate and sanitize input data to prevent inject
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Q3. What if your application is down for 1 hour in one site in prod?
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I would investigate the root cause, work on fixing the issue, and implement measures to prevent it from happening again.
• Investigate the root cause of the downtime, such as network issues, server failures, or software bugs

• Work on fixing the issue promptly to minimize impact on users and business operations

• Implement measures to prevent similar downtime in the future, such as redundancy, monitoring, and failover mechanism
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Q4. How do you make sure a throttling system process dropped messages from a slow downstream service?
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Implement a throttling system to handle dropped messages from a slow downstream service.
• Implement a queue to store messages from the downstream service.

• Set a maximum queue size and drop messages when the queue is full.

• Use a timestamp to track when messages were received and process them in order.

• Implement a retry mechanism to reprocess dropped messages after a certain time.

• Monitor the queue size and processing speed to
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Q1. System design basics
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Q2. Java 8 stream api code
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Q3. Current project
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Q1. Only arrogance related stuff
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Q2. Only arrogance related stuff happened
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I was asked two DSA questions and duration was of one hour.
1. Calculate Sum of edges of LinkedList
2. Given a list of numbers, find out all the pythagorean triplets.

This was also a DSA round for 1 hour and expected to solve two problems (Medium)

This was a system design round for one hour

Q1. Explain the last technically challenging topic that you have worked on. The engineering manager is only interested in self boasting. Without even trying to understand the entire problem statement, they try...read more
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Q1. Machine coding round for SQL
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Q1. Explain Concurrency
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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
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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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Implement thread safe load balancer.
focus on input validations and cover all corner cases in tests