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MVCC (Multiversion Concurrency Control)

MVCC (ya Multiversion Concurrency Control) ek database concurrency control technique hai jisme data…

Overview

MVCC (Multiversion Concurrency Control) — Quick Facts

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Property: Detail

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Full Name: Multiversion Concurrency Control

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Abbreviation: MVCC

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Type: Concurrency Control Mechanism

Topic 1

Infobox

📚 | Property | Detail | |---|---| | Full Name | Multiversion Concurrency Control | |…

Topic 2

Overview

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Option A: Lock-based — reader ko…

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Option B: MVCC — writer naya…

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Multi — ek data item ke multiple…

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Version — har write operation ek…

Topic 3

Background: Concurrency Problem

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Shared Lock (S-lock): Multiple…

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Exclusive Lock (X-lock): Sirf ek…

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Two-Phase Locking (2PL):…

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Reader blocks writer: Jab koi row…

Topic 4

Concurrency Anomalies

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Transaction A ne row update kiya…

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Transaction B woh uncommitted data…

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Agar A rollback kare, to B ne…

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MVCC prevention: B ko sirf…

Topic 5

How MVCC Works

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Purani row delete nahi hoti — woh…

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Ek new version create hoti hai…

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Dono versions me metadata hota…

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Har transaction ko ek unique,…

Topic 6

MVCC Version Chain Diagram

✨ `mermaid sequenceDiagram participant TX100 as Transaction 100 participant DB as Database…

Topic 7

MVCC vs Lock-Based Concurrency

🌟 | Aspect | MVCC | Lock-Based (2PL) | |---|---|---| | Core Mechanism | Multiple data…

Topic 8

Transaction Isolation Levels aur MVCC

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MVCC me practically use nahi hota

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Dirty reads allowed hain (uncommon…

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Most MVCC databases is level ko…

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Har statement ke liye naya…

Topic 9

MVCC in PostgreSQL

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xmin: Woh transaction ID jisne yeh…

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xmax: Woh transaction ID jisne yeh…

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Old row ka xmax set hota hai…

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New row create hoti hai with new…

Topic 10

MVCC in MySQL InnoDB

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Clustered Index: Primary key ke…

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Undo Log: Purane versions undo log…

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Read View: Transaction start hote…

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Purani row ka data undo log me…

Topic 11

MVCC in Oracle

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System Change Number (SCN):…

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Undo Tablespace: Old data versions…

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Consistent Read: Har query ko us…

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Read Consistency: Oracle me by…

Topic 12

MVCC in Other Databases

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By default SQL Server lock-based…

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Snapshot Isolation enable karne…

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Row versions tempdb me store hoti…

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READ_COMMITTED_SNAPSHOT isolation…

Topic 13

Database MVCC Implementation Comparison

Topic 14

Garbage Collection aur Version Cleanup

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Dead tuples (old versions jo kisi…

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Space OS ko return nahi karta —…

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Non-blocking — normal operations…

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autovacuum daemon periodically…

Topic 15

Write Conflicts aur Resolution

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Jo transaction pehle write kare,…

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Baad wala transaction…

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Application retry kar sakti hai

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Application-level decision — later…

Topic 16

Advantages of MVCC

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Readers kabhi block nahi hote —…

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Read-heavy workloads me dramatic…

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OLTP systems jahan high read…

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Read operations koi lock acquire…

Topic 17

Disadvantages of MVCC

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Multiple versions physically…

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PostgreSQL me table bloat ho sakta…

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InnoDB me undo log grow ho sakta…

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Additional storage cost

Topic 18

MVCC in Distributed Databases

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Clock Synchronization: Different…

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Global Snapshots: Distributed…

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Version Propagation: Ek node par…

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Hardware-based GPS + atomic clocks…

Topic 19

Best Practices

🎯 For Application Developers 1. Transactions chhote rakho — long-running transactions old…

Comparison

MVCC vs Lock-Based Concurrency

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Core Mechanism: Multiple data versions

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Readers block Writers?: No ❌

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Writers block Readers?: No ❌

Comparison

Database MVCC Implementation Comparison

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PostgreSQL: Append-only (new tuple)

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MySQL/InnoDB: In-place + Undo

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Oracle: In-place + Undo

Diagram

Visual Flow

📊 Diagram visualization — details in narration

Quiz — Question 1

MVCC (Multiversion Concurrency Control) ka sabse sahi definition kya hai?

Quick Quiz

Quiz — Question 2

MVCC (Multiversion Concurrency Control) ka 'Full Name' kya hai?

Complete! 🎉

MVCC (Multiversion Concurrency Control) Complete!

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MVCC (Multiversion Concurrency Control) Complete

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