DD Unit-3 notes

https://drive.google.com/file/d/1OINF-ntNdWyB1P918kieUO4q40olDW7W/view?usp=sharing https://drive.google.com/file/d/1VuIWB22qpFL5phGbmBatx0oiLYwbKRob/view?usp=sharing

This document provides an educational overview of database transactions, concurrency control, and deadlock handling, fundamental concepts in Distributed Database Management Systems (DDBMS). A transaction, treated as an atomic unit, must adhere to ACID properties: Atomicity, Consistency, Isolation, and Durability, and progresses through states like Active, Partially Committed, and Committed. Concurrent execution, while allowing multiple users to access the database simultaneously, introduces problems like Lost Update (W-W Conflict), Dirty Read (W-R Conflict), and Unrepeatable Read (W-R Conflict). Concurrency control protocols, such as Lock-Based, Time Stamp, and Optimistic, ensure data consistency and serializability. Deadlocks, a state where transactions wait indefinitely for locks held by others, are managed through prevention, avoidance (like Wait-Die and Wound-Wait), or detection and removal techniques. These concepts are also adapted for distributed systems.

Here are 5 key bullet points of the specific topics covered with a brief definition for each:

• ACID Properties: A set of properties (Atomicity, Consistency, Isolation, Durability) that a transaction in a database system must maintain to ensure accuracy, completeness, and data integrity.
• Serial Schedule: A type of schedule where one transaction is executed completely before starting another transaction, with no interleaving of operations.
• Conflict Serializability: A schedule is called conflict serializability if it can be transformed into a serial schedule by swapping non-conflicting operations, or if it is conflict equivalent to a serial schedule.
• Two-phase locking (2PL): A protocol that divides the execution phase of a transaction into three parts: seeking permission for locks, acquiring all locks (growing phase), and releasing acquired locks (shrinking phase), without demanding any new locks once releasing starts.
• Deadlock: A state in a database system with two or more transactions, where each transaction is waiting for a data item that is being locked by another transaction.