Round 1 : Organised by thirdparty

1. Explain the significance of transaction management in Spring Boot applications, focusing on the @Transactional annotation.
   Additionally, elaborate on the various isolation levels supported by transaction management and discuss scenarios where each isolation level is most appropriate.

2. You are tasked with designing a messaging application that supports real-time communication between users. Users can exchange text messages, images, and files.
   Given this scenario, which design patterns would you choose to implement various aspects of the messaging application, and why? Discuss the use cases of each selected design pattern.

3. Explain the concepts of Kafka partitions, rebalancing, and the significance of partition keys in a Kafka setup. Additionally, can you demonstrate how you would implement a partition key strategy in a Java Kafka producer application?

4. Consider a scenario where you have a relational database schema for an e-commerce platform with three main tables: products, orders, and users. The products table contains information about various products available on the platform, the orders table tracks details of customer orders, and the users table stores user information.
   Given this schema, please write a SQL query to retrieve the total number of orders placed by users who have made purchases of products within a specific category.
   products table
   product_id, product_name, category_id,
   orders table
   order_id, user_id, product_id, order_date

5. coding : https://leetcode.com/problems/simple-bank-system/description/

Round 2 : LLD Organised by thirdparty
LLD of Hotel booking. - DBschema, API and how to handle concurrency.
ACID and Isolation level and few questions on kafka.

Round 3 - Cars24 Panel : Was inforned to be behavioral round but turned out to be another LLD /machine code. (So don't trust over words of HR.)
LLD code of Cart Service.

Code close to production ready using design pattern and handling concurrency. Was speaking loud during whole process. Nothing from Panelist in whole period, when i was done he just asked me about API retry strategy.
From my end, i felt round went well as there were no major question from interviewer.

Verdict : Reject.