17. Change Streams: Building Real-Time Event-Driven Pipelines with MongoDB • MongoDB & NoSQL Architecture: CRUD to Sharding & WiredTiger • Rishabh Ki Kaksha

MongoDB & NoSQL Architecture: CRUD to Sharding & WiredTiger › 17. Change Streams: Building Real-Time Event-Driven Pipelines with MongoDB

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Course Syllabus

Module 1: MongoDB Foundations, BSON & CRUD Mechanics

01. NoSQL vs SQL: CAP Theorem & Document-Oriented Architecture 02. BSON Data Types & Document Schema Design (Embedding vs Referencing) 03. High-Performance CRUD Operations, BulkWrite & Write Concerns 04. Schema Validation with JSON Schema ($jsonSchema)

Module 2: Advanced Aggregation Framework & Data Pipelines

05. Aggregation Pipeline Core: $match, $project, $group, $sort & $limit 06. Complex Transformations: $unwind, $lookup (Joins) & $facet (Multi-Facet Analytics) 07. Window Operators ($setWindowFields) & Accumulator Functions

Module 3: Indexing Strategies & Query Optimization

08. B-Tree Indexes in MongoDB: Single Field, Compound & Partial Indexes 09. Special Indexes: TTL (Time-To-Live), Geospatial (2dsphere) & Text Indexes 10. Query Profiling, explain("executionStats") & Index Covering Analysis

Module 4: Storage Engine Internals (WiredTiger) & ACID Transactions

11. WiredTiger Storage Engine Architecture: Cache, Compression & Checkpoints 12. Read Concerns (local, majority, linearizable) & Write Concerns (w:majority, j:true) 13. Multi-Document Distributed ACID Transactions with Sessions

Module 5: High Availability, Replica Sets, Sharding & Backups

14. Replica Sets Architecture: Primary Election, Oplog & Automatic Failover 15. Sharding Architecture: mongos Router, Config Servers & Shard Key Selection 16. Range vs Hash Sharding, Chunk Balancing & Jumbo Chunks Mitigation 17. Change Streams: Building Real-Time Event-Driven Pipelines with MongoDB 18. Production Backup Strategies: mongodump/mongorestore, Point-in-Time & Atlas CLI

Interactive Lesson Studio

# 17. Change Streams: Building Real-Time Event-Driven Pipelines with MongoDB

> MongoDB Notes by Rishabh - Topic 17

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### 1. Change Streams Kya Hain? (The Real-Time Event Bus ⚡)

Pehle real-time updates ke liye polling ya application code me duplicate emit events karne padte the.  
**MongoDB Change Streams** collection me hone wale har **Insert, Update, Delete, Replace event ko real-time me stream karta hai!**

---

### 2. Node.js Real-Time Change Stream Implementation

```typescript
const collection = db.collection('orders');

// Watch with Aggregation Filter (Only watch High-Value Orders > 10,000):
const changeStream = collection.watch([
    {
        $match: {
            "operationType": { $in: ["insert", "update"] },
            "fullDocument.totalAmount": { $gte: 10000 }
        }
    }
], { fullDocument: "updateLookup" });

changeStream.on("change", (next) => {
    console.log("🔔 Real-Time Order Event:", next.operationType);
    console.log("📦 Updated Document Payload:", next.fullDocument);

// Push notification via WebSockets or publish to Kafka/RabbitMQ:
    io.emit("vip-order-placed", next.fullDocument);
});
```

---

### 3. Resume Tokens (Network Glitch Immunity 🛡️)

Agar Node.js server 10 minute ke liye disconnect ho jaye:
*   Change Stream ke paas **`_data` Resume Token** hota hai.
*   Reconnect hone par `collection.watch([], { resumeAfter: lastResumeToken })` pass karne se **disconnect ke dauran chhoote huye saare events zero-loss replay ho jaate hain!**

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### 4. Master Comparison Matrix

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### 5. Interview Ke 3 Sawal Is Topic Se

1. **Change Streams chalane ke liye kya prerequisite zaroori hai?** -> MongoDB ka Replica Set ya Sharded Cluster me hona mandatory hai (Standalone single `mongod` instances me Change Streams work nahi karte).
2. **`fullDocument: "updateLookup"` option kya karta hai?** -> Default update event sirf delta changes (`updatedFields`) bhejta hai; ye option poora latest document fetch karke event payload me provide karta hai.
3. **Change Stream resume token kitni der tak valid rehta hai?** -> Jab tak Oplog me wo specific timestamp overwrite na ho jaye (Oplog retention window).

---
**Next Topic:** 18. Production Backup Strategies: mongodump/mongorestore, Point-in-Time & Atlas CLI

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Rishabh Gehlot

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