11. Transaction Isolation Levels: Read Uncommitted, Read Committed, Repeatable Read (Default) & Serializable • MySQL Mastery: Basic to Advanced & Enterprise Scaling • Rishabh Ki Kaksha

MySQL Mastery: Basic to Advanced & Enterprise Scaling › 11. Transaction Isolation Levels: Read Uncommitted, Read Committed, Repeatable Read (Default) & Serializable

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Course Syllabus

Module 1: Relational Algebra, SQL Fundamentals & Schema Design

01. Relational Database Foundations: SQL vs NoSQL, Relational Algebra & Database Normalization (1NF to BCNF) 02. MySQL Data Types Deep Dive: VARCHAR vs TEXT, DECIMAL for Financial Precision & JSON Column Performance 03. Primary Keys, Foreign Keys, Unique Constraints & Referential Integrity Rules (CASCADE / RESTRICT)

Module 2: Advanced SQL: Joins, Window Functions & CTEs

04. SQL Joins Masterclass: INNER, LEFT, RIGHT, FULL OUTER & Cross Joins Execution Strategies 05. Subqueries vs Common Table Expressions (WITH CTE) & Recursive CTEs for Hierarchical Tree Queries 06. SQL Window Functions: ROW_NUMBER(), RANK(), DENSE_RANK(), NTILE(), LEAD() & LAG() for Analytics

Module 3: InnoDB Storage Engine Internals, Buffer Pool & B+ Trees

07. InnoDB Architecture: The Buffer Pool, Change Buffer, Redo Log (WAL), Undo Log & Doublewrite Buffer 08. Clustered Indexes vs Secondary Indexes: How B+ Tree Data Pages are Organized on Disk 09. The B+ Tree Node Structure: Fanout, Height Calculations & Why B+ Trees Outperform Binary Trees for Disk I/O

Module 4: ACID Transactions, Lock Architecture & Concurrency Control

10. ACID Properties Deep Dive: Atomicity (Undo Log), Consistency, Isolation & Durability (Redo Log) 11. Transaction Isolation Levels: Read Uncommitted, Read Committed, Repeatable Read (Default) & Serializable 12. Multi-Version Concurrency Control (MVCC): Read Views, Row Versioning & Non-Locking Consistent Reads 13. InnoDB Locking Engine: Record Locks, Gap Locks, Next-Key Locks & Resolving Deadlocks in High Concurrency

Module 5: Query Optimization, Index Tuning, Partitioning & High Availability

14. Query Optimization with EXPLAIN & EXPLAIN ANALYZE: Type column (ALL, index, range, ref, eq_ref, const) 15. Index Tuning Secrets: Leftmost Prefix Rule, Covering Indexes (Using Index) & Avoiding Index Degradation Traps 16. Table Partitioning: Range, List, Hash & Key Partitioning for Multi-Million Row Tables 17. MySQL Replication: Binary Log (binlog), Master-Slave Async vs Semi-Sync Replication & GTID Architecture 18. Production Enterprise Backup Strategies: Physical (Percona XtraBackup) vs Logical (mysqldump / mydumper)

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# 11. Transaction Isolation Levels: Read Uncommitted, Read Committed, Repeatable Read (Default) & Serializable

> MySQL Mastery Notes by Rishabh - Topic 11

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### 1. The 4 Isolation Levels & Concurrency Phenomena ⚖️

```sql
SET TRANSACTION ISOLATION LEVEL REPEATABLE READ;
```

1. **Dirty Read:** Uncommitted data read karna jo baad me rollback ho jaye.
2. **Non-Repeatable Read:** Same query transaction me 2 baar chalane par beech me doosre commit hone se row data badal jana.
3. **Phantom Read:** Range query chalane par beech me nayi inserted rows match ho jana.

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### 2. Master Isolation Matrix

| Isolation Level | Dirty Read | Non-Repeatable Read | Phantom Read | Locking Mechanism |
| :--- | :--- | :--- | :--- | :--- |
| **Read Uncommitted** | ⚠️ Yes | ⚠️ Yes | ⚠️ Yes | No read locks |
| **Read Committed (Postgres Standard)**| ❌ No | ⚠️ Yes | ⚠️ Yes | Read View on every query |
| **Repeatable Read (MySQL Default 👑)**| ❌ No | ❌ No | ❌ **No (Prevented via Gap Locks + MVCC!)**| Read View on Tx start |
| **Serializable** | ❌ No | ❌ No | ❌ No | Pessimistic Shared Locks |

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

1. **MySQL InnoDB Repeatable Read me Phantom Read kaise eliminate karta hai?** -> Consistent reads MVCC Read View se eliminate hoti hain aur locking reads (`SELECT FOR UPDATE`) Next-Key Locks (Record + Gap lock) se eliminate hoti hain.
2. **Read Committed vs Repeatable Read me Read View creation timing ka kya difference hai?** -> Read Committed me har individual `SELECT` statement par naya Read View banta hai; Repeatable Read me transaction ke pehle `SELECT` par single immutable Read View banta hai.
3. **Serializable isolation level production OLTP me kyu rarely use hota hai?** -> Kyunki saari reads shared locks acquire karti hain jisse high concurrency me massive deadlock aur lock wait timeout errors aane lagte hain.

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**Next Topic:** 12. Multi-Version Concurrency Control (MVCC): Read Views, Row Versioning & Non-Locking Consistent Reads

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