unit 4 Dbms notes

https://drive.google.com/file/d/1Gur3HX4BjLFHsLcutwuTy9i0r_ug7S8A/view?usp=sharing

The document, dbms unit-4.pdf, focuses on the core concepts of transaction management and concurrency control in Database Management Systems (DBMS). A transaction is defined as a group of tasks or a series of actions performed by a single user to access and manipulate the database contents. To maintain data integrity, transactions must adhere to the ACID properties: Atomicity (all or nothing), Consistency (maintaining integrity constraints), Isolation (transactions are isolated from each other), and Durability (permanent changes survive failures). The process of concurrent execution, where multiple users access the same database simultaneously, introduces challenges like the Lost Update, Dirty Read, and Unrepeatable Read problems. To manage these issues and ensure serializability, the document discusses Concurrency Control protocols, including Lock-Based protocols (like Two-Phase Locking-2PL), Timestamp Ordering protocols, and Validation-Based protocols. Additionally, it covers transaction states, the recoverability of schedules, and log-based recovery mechanisms.

Here are 5 key bullet points of the specific topics covered:

• Transaction Concept: A transaction is an action or series of actions performed by a single user to access the contents of the database.
• ACID Properties: The four properties—Atomicity, Consistency, Isolation, and Durability—that transactions must have to maintain consistency in a database before and after the transaction.
• Concurrency Control Protocols: Management procedures required for controlling concurrent execution of operations to avoid inconsistencies, categorized into Lock-Based, Timestamp Ordering, and Validation-Based protocols.
• Conflict Issues (Problems with Concurrent Execution): Issues like the Lost Update problem (Write-Write conflict), Dirty Read problem (Write-Read conflict), and Unrepeatable Read problem (Write-Read conflict) that occur when operations are not performed in an interleaved manner.
• Serializability: A property of non-serial schedules where the result is equivalent to the result of its transactions executed serially, ensuring correct execution of interleaved operations.