09. Special Indexes: TTL (Time-To-Live), Geospatial (2dsphere) & Text Indexes • MongoDB & NoSQL Architecture: CRUD to Sharding & WiredTiger • Rishabh Ki Kaksha

MongoDB & NoSQL Architecture: CRUD to Sharding & WiredTiger › 09. Special Indexes: TTL (Time-To-Live), Geospatial (2dsphere) & Text Indexes

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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

# 09. Special Indexes: TTL (Time-To-Live), Geospatial (2dsphere) & Text Indexes

> MongoDB Notes by Rishabh - Topic 09

---

### 1. TTL Indexes (Auto-Expiring Documents ⏳)

Session tokens, OTP codes ya temporary cache ko automatically database se delete karna:

```javascript
// OTP collection: Document 300 seconds (5 mins) baad auto-delete ho jayega!
db.otps.createIndex(
    { createdAt: 1 },
    { expireAfterSeconds: 300 }
);

// Insert OTP:
db.otps.insertOne({ phone: "+919876543210", otp: "458921", createdAt: new Date() });
```

---

### 2. Geospatial 2dsphere Indexes (Uber / Swiggy Nearby Search 📍)

Earth ke sphere coordinates (Longitude, Latitude) par fast distance calculation:

```javascript
// 1. Create 2dsphere index:
db.restaurants.createIndex({ location: "2dsphere" });

// 2. Query: Find all restaurants within 5 km (5000 meters) of user:
db.restaurants.find({
    location: {
        $near: {
            $geometry: { type: "Point", coordinates: [77.2090, 28.6139] }, // [Lng, Lat]
            $maxDistance: 5000 // In meters!
        }
    }
});
```

---

### 3. Full-Text Search Indexes with Relevance Scoring 🔍

```javascript
// 1. Text index across multiple fields:
db.articles.createIndex({ title: "text", content: "text" });

// 2. Search & Sort by Text Score Relevance:
db.articles.find(
    { $text: { $search: "react nodejs performance" } },
    { score: { $meta: "textScore" } }
).sort({ score: { $meta: "textScore" } });
```

---

### 4. Master Comparison Matrix

| Special Index | Field Type | Key Operator | Production Use Case |
| :--- | :--- | :--- | :--- |
| **TTL** | `Date` object | `expireAfterSeconds` | Auth sessions, Temp uploads, OTPs |
| **2dsphere** | GeoJSON `{ type: "Point", coordinates }`| `$near`, `$geoWithin` | Food delivery, Ride hailing, Store finders |
| **Text** | `string` | `$text`, `$meta: "textScore"`| Blog search, Product catalog lookup |

---

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

1. **TTL index background task kitni der me run hota hai?** -> MongoDB ka internal TTL thread har 60 seconds me ek baar run hokar expired documents ko batch delete karta hai.
2. **GeoJSON me coordinates ka order kya hota hai?** -> Hamesha **`[Longitude, Latitude]`** (`[X, Y]`); `[Latitude, Longitude]` pass karne par query fail ho jayegi!
3. **Ek collection me kitne Text Indexes ho sakte hain?** -> Maximum 1 Text Index (lekin wo single index multiple fields ko combine kar sakta hai compound text index ke roop me).

---
**Next Topic:** 10. Query Profiling, explain("executionStats") & Index Covering Analysis

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