11. WiredTiger Storage Engine Architecture: Cache, Compression & Checkpoints • MongoDB & NoSQL Architecture: CRUD to Sharding & WiredTiger • Rishabh Ki Kaksha

MongoDB & NoSQL Architecture: CRUD to Sharding & WiredTiger › 11. WiredTiger Storage Engine Architecture: Cache, Compression & Checkpoints

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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

# 11. WiredTiger Storage Engine Architecture: Cache, Compression & Checkpoints

> MongoDB Notes by Rishabh - Topic 11

---

### 1. WiredTiger Storage Engine Architecture 🧠

MongoDB ka core storage engine **WiredTiger** hai:

```
[ Incoming Read/Write ]
           ⬇
┌─────────────────────────────────────────────────────────────┐
│ 1. WIREDTIGER IN-MEMORY CACHE                               │
│ (Holds uncompressed dirty pages in RAM - 50% of Total RAM)  │
└──────────────────────────────┬──────────────────────────────┘
                               ⬇
┌─────────────────────────────────────────────────────────────┐
│ 2. WRITE-AHEAD LOGGING (Journaling - Instant Durability)   │
└──────────────────────────────┬──────────────────────────────┘
                               ⬇ (Every 60 Seconds Checkpoint)
┌─────────────────────────────────────────────────────────────┐
│ 3. ON-DISK COMPRESSED DATA FILES (Snappy / zlib block store)│
└─────────────────────────────────────────────────────────────┘
```

---

### 2. WiredTiger Cache Allocation Formula

By default, WiredTiger kitni RAM use karta hai:
```
WiredTiger Cache Size = 50% of (Total RAM - 1 GB)
```
*(Example: 16GB RAM server par WiredTiger Cache ~7.5 GB RAM allocate karta hai).*

---

### 3. Checkpoints & The Journaling Safety Net 🛡️

*   **Checkpoints:** Har 60 seconds me WiredTiger RAM ke saare dirty pages ko disk par snapshot write karta hai.
*   **Journal (WAL):** Agar 59th second par power disconnect ho jaye, toh MongoDB restart hone par Journal replay karke aakhri 59 seconds ka data 100% recover kar leta hai!

---

### 4. Master Comparison Matrix

---

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

1. **WiredTiger Cache aur OS File System Cache me kya difference hai?** -> WiredTiger cache uncompressed data rakhta hai direct fast access ke liye; OS Cache disk se read kiye gaye raw compressed blocks ko hold karta hai.
2. **Eviction Server WiredTiger me kab trigger hota hai?** -> Jab WiredTiger memory usage 80% dirty threshold cross karti hai, tab background eviction threads purane clean pages ko release karke RAM free karte hain.
3. **Document-level concurrency control WiredTiger me kaise kaam karti hai?** -> Multi-Version Concurrency Control (MVCC) use karke lock-free concurrent reads aur individual document level write locks manage karta hai.

---
**Next Topic:** 12. Read Concerns (local, majority, linearizable) & Write Concerns (w:majority, j:true)

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