CQRS Design Pattern in Microservices Interview Questions and Answers | Code Decode

In this video of code decode we have explained cqrs design pattern in microservice which is common questions asked for fresher and experienced Udemy Course Discounted Link https://www.udemy.com/course/master-spring-boot-microservice-angular-with-k8s-cicd-aws/?couponCode=BLACKFRIDAY2024 If you want to participate in Mock Interview send your nominations using the below google form https://forms.gle/yfxTWUnzWhwpRM1WA ### **1. What is CQRS?** CQRS (Command Query Responsibility Segregation) is an architectural pattern that **separates read (query) and write (command) operations** into different models, databases, or services. This helps optimize performance, scalability, and security in distributed systems. ### **2. Why Use CQRS?** Traditional CRUD (Create, Read, Update, Delete) architectures often use the **same model and database** for both read and write operations. This leads to several challenges: ❌ **Scalability Issues** → High read traffic can slow down writes and vice versa. 🔹 **Increased Database Locks:** - [ ] Many databases **lock rows or tables** while executing queries. - [ ] Long-running read queries (e.g., complex joins, analytics) can prevent **timely updates** to data. 🔹 **Index Overhead:** - [ ] Queries rely on **indexes** for faster lookups, but **each write modifies indexes**. - [ ] More reads mean **heavier index usage**, slowing down insert/update operations. 🔹 **I/O and Memory Contention:** - [ ] Reads and writes compete for **RAM, CPU, and disk I/O**. - [ ] Frequent read queries increase **buffer pool usage**, leaving fewer resources for writes. ❌ **Data Model Conflicts** → Read operations may require denormalized data, while writes need strict validation. ### **3. CQRS Architecture Overview** 🚀 **Two Separate Models:** - **Command Model (Write Side)** → Handles data modifications (create, update, delete). - **Query Model (Read Side)** → Optimized for fast data retrieval (Query). 🚀 **Two Separate Databases (Optional):** - The **write database** is normalized for consistency (SQL, PostgreSQL, MySQL). - The **read database** is optimized for queries (NoSQL, Elasticsearch, Redis, Materialized Views). 🚀 **Communication Mechanism:** - **Event-driven approach** (Kafka, RabbitMQ, or Event Store) syncs read and write models asynchronously. ### **4. How CQRS Works (Step-by-Step)** 1️⃣ **User sends a command** (e.g., "Create Order"). 2️⃣ The **Command Model** validates and processes the request. 3️⃣ Data is stored in the **Write Database**. 4️⃣ An **event is published** (e.g., "OrderCreatedEvent"). 5️⃣ The **Query Model** listens to events and updates the Read Database. 6️⃣ When the user requests data (e.g., "Get Order History"), the system **fetches from the Read Database**, which is optimized for fast queries. To implement this using [CQRS ](https://www.java67.com/2023/01/what-is-cqrs-command-query.html)in a Spring Boot microservices architecture, we could have separate microservices for the Command and Query sides. The Command microservice would handle product creation, updates, and deletions, and it would publish events to a Kafka topic whenever a product is created, updated, or deleted. The Query microservice would subscribe to this Kafka topic and update its own data store with the latest product information. It would expose a set of REST endpoints that allow users to search for products based on various criteria. The Query microservice could use Elasticsearch or another search engine to provide fast search capabilities. Mock Interview Playlist: https://www.youtube.com/playlist?list=PLyHJZXNdCXsdKpIT19C1nlZH_HROXyROF Most Asked Core Java Interview Questions and Answers: https://youtube.com/playlist?list=PLyHJZXNdCXscoyL5XEZoHHZ86_6h3GWE1 Advance Java Interview Questions and Answers: https://youtube.com/playlist?list=PLyHJZXNdCXsexOO1VQ4vs-BM2-8CKrixd Java 8 Interview Questions and Answers: https://youtube.com/playlist?list=PLyHJZXNdCXsdeusn4OM33415DCMQ6sUKy Hibernate Interview Questions and Answers: https://youtube.com/playlist?list=PLyHJZXNdCXsdC-p2186C6NO4FpadnCC_q Spring Boot Interview Questions and Answers: https://youtube.com/playlist?list=PLyHJZXNdCXsexOO1VQ4vs-BM2-8CKrixd Angular Playlist: https://www.youtube.com/watch?v=CAl7RQSdq2Q&list=PLyHJZXNdCXsfxRtDwtGkDD_lLfTWc1g0i SQL Playlist: https://www.youtube.com/playlist?list=PLyHJZXNdCXse86eLuwy5uZohd_bddE9Ni GIT: https://youtube.com/playlist?list=PLyHJZXNdCXscpl6pxOnL2lRWJlzvzjyZE Subscriber and Follow Code Decode Subscriber Code Decode: https://www.youtube.com/c/CodeDecode?sub_confirmation=1 LinkedIn : https://www.linkedin.com/in/codedecodeyoutube/ Instagram: https://www.instagram.com/codedecode25/ #springboot3 #codedecode #interviewquestions