13. InnoDB Locking Engine: Record Locks, Gap Locks, Next-Key Locks & Resolving Deadlocks in High Concurrency • MySQL Mastery: Basic to Advanced & Enterprise Scaling • Rishabh Ki Kaksha

MySQL Mastery: Basic to Advanced & Enterprise Scaling › 13. InnoDB Locking Engine: Record Locks, Gap Locks, Next-Key Locks & Resolving Deadlocks in High Concurrency

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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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# 13. InnoDB Locking Engine: Record Locks, Gap Locks, Next-Key Locks & Resolving Deadlocks in High Concurrency

> MySQL Mastery Notes by Rishabh - Topic 13

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### 1. The 3 Core Row Lock Types 🔒

1. **Record Lock:** Exact single index record par lock (e.g. `WHERE id = 5`).
2. **Gap Lock:** Index records ke beech ke empty gap space par lock (e.g. Gap between $(5, 10)$). Prevent karta hai doosre transactions ko beech me nayi row insert karne se!
3. **Next-Key Lock (Record Lock + Gap Lock):** Half-open interval $(5, 10]$ lock karta hai (InnoDB default!).

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### 2. Deadlock Detection & Resolution ⚡

Tx A holds Lock 1, requests Lock 2; Tx B holds Lock 2, requests Lock 1 (**Deadlock Cycle!**).  
*   **InnoDB Deadlock Detector (`innodb_deadlock_detect = ON`):** Instantly wait-for graph cycle detect karta hai aur **Sabse kam rows modify karne wali transaction ko auto-rollback karta hai!**

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

1. **Gap Locks Read Committed isolation level par disable kyu ho jaate hain?** -> Read Committed me phantom read prevention mandatory nahi hoti, isliye Gap Locks completely deactivate ho jate hain (Locks only exact records).
2. **Intention Locks (`IS` / `IX`) table level par kyu acquire hote hain?** -> Taaki koi doosri transaction table-level lock (`ALTER TABLE`) acquire karne se pehle instant check kar sake ki table ke andar kisi row par lock hai ya nahi ($O(1)$ check vs full row scan).
3. **Application level par Deadlocks kaise minimize kiye jaate hain?** -> Hamesha multi-table updates ko consistent resource ordering me acquire karna (e.g. Always update User A before User B).

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**Next Topic:** 14. Query Optimization with EXPLAIN & EXPLAIN ANALYZE: Type column (ALL, index, range, ref, eq_ref, const)

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