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DBMS Topics

Hub Unit 1 — Introduction to DBMS & Entity-Relationship Model Advantages and Disadvantages of DBMS Aggregation Characteristics of DBMS Data Independence Data Models Database Users and Administrators DBMS Languages ER Diagrams Entity-Relationship ER Model Introduction to DBMS Keys in DBMS Relationships and Cardinality Schema and Instance Specialization and Generalization Unit 1 Summary — Introduction to DBMS & ER Model Three-Level Architecture ANSI/SPARC Architecture Weak Entity Set Unit 2 — Relational Model & SQL Constraints in SQL Cursors DCL and TCL Commands DDL Commands DML Commands Domain Relational Calculus DRC Functions and Stored Procedures Joins in SQL Nested Queries Subqueries Relational Algebra Relational Calculus Relational Model SQL Introduction Unit 2 Summary — Relational Model & SQL Triggers in SQL Tuple Relational Calculus TRC Views in SQL Armstrong's Axioms & Closure of Attributes Boyce-Codd Normal Form BCNF Closure of Attributes Dependency Preservation Fifth Normal Form 5NF First Normal Form 1NF Fourth Normal Form 4NF Functional Dependency Lossless Decomposition Multivalued Dependency Normal Forms — Overview Normalization — Introduction Second Normal Form 2NF Unit 3 Summary — Normalization Third Normal Form 3NF Unit 4 — Transaction Management & Concurrency Control ACID Properties Checkpoints Concurrency Control & Serializability Deadlock in DBMS Lock-Based Protocols & Two-Phase Locking Log-Based Recovery Recovery System Serializability Shadow Paging Unit 4 Summary — Transaction Management & Concurrency Control Timestamp-Based Protocol Transaction Management Transaction States Two-Phase Locking 2PL Unit 5 — Storage & Indexing B+ Tree B-Tree Cost Estimation Dynamic Hashing File Organization Hashing Techniques Indexing — Introduction Multi-Level Indexing Query Optimization Query Processing Single-Level Indexing Static Hashing Unit 5 Summary — Storage & Indexing Unit 6 — Advanced Topics in DBMS Big Data and DBMS Cloud Database Data Mining Data Warehouse Database Security Distributed Database Distributed Query Processing Distributed DBMS Architecture, Fragmentation & Replication MongoDB — Introduction NoSQL Database Replication in Distributed Databases Unit 6 Summary — Advanced Topics in DBMS Viva Voce — DBMS Important Viva Questions — DBMS Interview Questions — DBMS Viva Answers — DBMS DBMS Multiple Choice Questions MCQs DBMS Lab Programs

Unit 4 Summary — Transaction Management & Concurrency Control

Last Updated : 21 May, 2026

Unit 4132 words10 headingsTables includedExamples included

Quick Reference

Transaction States

Active → Partially Committed → Committed ↓ (failure) Failed → Aborted

ACID Properties

Property	Ensures	Mechanism
Atomicity	All-or-nothing	Undo log, Rollback
Consistency	Valid state → Valid state	Constraints, App logic
Isolation	No interference	Locks, MVCC
Durability	Committed = Permanent	WAL, Checkpoints

Concurrency Problems

Problem	Description	Fix
Dirty Read	Read uncommitted data	Strict 2PL / Read Committed
Lost Update	Write overwritten by another	Exclusive locks
Non-Repeatable Read	Same read gives different values	Repeatable Read isolation
Phantom Read	New rows appear between reads	Serializable isolation

Serializability Test

Ti	Tj if Ti's operation conflicts with and precedes Tj's
No cycle in graph	Conflict Serializable ✓
Cycle exists	NOT serializable ✗

2PL Variants

Basic 2PL	Serializable; cascading rollbacks possible
Strict 2PL	X-locks held till commit; no dirty reads
Rigorous 2PL	All locks held till commit; simplest

Deadlock Handling

Strategy	Method
Detection	Wait-For Graph cycle check; abort victim
Wait-Die	Older waits; younger aborts
Wound-Wait	Older preempts; younger waits
Prevention	Acquire locks in global order

Timestamp Protocol Rules

TS(Ti) < W-ts(X)	ABORT Ti
else	proceed, update R-ts(X)
TS(Ti) < R-ts(X)	ABORT Ti
TS(Ti) < W-ts(X)	ABORT Ti (or ignore — Thomas' Rule)
else	proceed, update W-ts(X)

Recovery Methods Comparison

Log-Based (WAL)	Write log first, then data. UNDO+REDO on crash.
Checkpoints	Periodic log truncation; faster recovery.
Shadow Paging	Maintain old page table; instant recovery; no log.

Recovery After Crash (Log-Based)

1. Analysis	Find REDO set (committed) and UNDO set (incomplete)
2. REDO pass	Re-apply committed changes (oldest log record first)
3. UNDO pass	Reverse incomplete changes (newest log record first)

Exam Focus

Revise definitions, diagrams, examples, and short-answer points for Unit 4 Summary — Transaction Management & Concurrency Control.

Interview Use

Prepare one clear explanation, one practical example, and one common mistake for this DBMS topic.

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Unit 4Unit 4 — Transaction Management & Concurrency ControlThis unit covers how databases maintain data integrity when multiple operations execute simultaneously or when system failures occur. Transactions are the fundamental uni Unit 4Concurrency Control & SerializabilityConcurrency control is the mechanism that ensures correct results when multiple transactions execute simultaneously, without interfering with each other.Unit 4Transaction ManagementA transaction is a logical unit of work consisting of one or more database operations reads/writes that must be executed as a single indivisible unit. Either ALL operatio Unit 4Transaction StatesA transaction passes through a series of well-defined states during its lifetime. The DBMS tracks the state of every transaction to manage concurrency and recovery correc Unit 4ACID PropertiesACID is an acronym for the four key properties that every database transaction must satisfy to ensure data validity even in cases of errors, power failures, and concurren Unit 4CheckpointsA checkpoint is a snapshot mechanism where the DBMS periodically writes all dirty modified buffer pages to disk and records the state of active transactions in the log.

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