Database Management Systems Chapter 18

Questions and Answers

What describes a transaction in a DBMS?

A series of database schema modifications.

A sequence of reads and writes to the database. (correct)

The total number of operations in a DBMS.

An isolated execution of a database program.

Which property ensures that transactions are treated as a single unit of work?

Consistency

Atomicity (correct)

Isolation

Durability

What is a serial schedule in transaction management?

A schedule that does not interleave the actions of different transactions. (correct)

A schedule where only read operations are performed.

A schedule that guarantees data integrity.

A schedule that allows multiple transactions to run simultaneously.

What does a serializable schedule represent?

<p>A schedule that is equivalent to some serial execution of the transactions.</p> Signup and view all the answers

What happens if a transaction aborts in a DBMS?

<p>The DBMS undoes the changes made by the transaction.</p> Signup and view all the answers

Study Notes

Transactions Overview

Concurrent execution of user programs enhances DBMS performance.
A transaction acts as an abstract representation of a user's operations, focusing on database read/write activities.

Concurrency in DBMS

Users perceive each transaction as executing independently.
The DBMS manages concurrency by interleaving actions (reads and writes) of multiple transactions.
Transactions must maintain database consistency, ensuring the database remains in a consistent state post-execution.

Atomicity of Transactions

Transactions can either commit after all actions are executed or abort before completion.
Atomicity is a critical property ensured by the DBMS, meaning that either all actions are completed, or none are applied.
The DBMS logs transaction actions, enabling it to revert any changes made by aborted transactions.

Example of Transactions

Two transactions example:
- T1: Increments A by 100 and decrements B by 100.
- T2: Multiplies A and B by 1.06.
There is no guaranteed execution order between T1 and T2; however, their net effect must mirror the result of executing them sequentially.

Scheduling Transactions

Serial Schedule: A type of scheduling where transaction actions do not intermingle.
Equivalent Schedules: Two schedules are considered equivalent if executing them yields the same database state.
Serializable Schedule: A schedule that can be rearranged to match the outcome of some serial execution of transactions.

Description

Explore the intricacies of transaction management in database systems in this quiz. Delve into the concepts of concurrent execution and the importance of transactions in maintaining database integrity. Test your understanding of how DBMS handles multiple operations efficiently.