Database Management Systems Chapter 18 Part 2

Questions and Answers

What is the primary purpose of Strict Two-phase Locking (Strict 2PL) protocol in transaction management?

To ensure that all transactions are executed in a serializable manner (correct)

To allow concurrent transactions without restrictions

To facilitate faster read operations

To minimize memory usage during transaction execution

What must happen if a transaction Ti is aborted?

Only the last action performed by Ti must be undone

All actions of Ti must be undone and any transaction reading from Ti must also be aborted (correct)

All its actions are final and cannot be undone

Ti's locks are released immediately after aborting

During which phase of the Aries recovery algorithm are dirty pages updated in the buffer pool?

Commit Phase

Redo Phase (correct)

Analysis Phase

Undo Phase

What triggers the release of a transaction's locks in a DBMS according to the content?

<p>At the time of transaction completion only if committed</p> Signup and view all the answers

Why is it essential to write log records to disk before the changed page in transaction management?

<p>To maintain a proper order of operations for recovering from crashes</p> Signup and view all the answers

Study Notes

Transaction Management Overview

Anomalies can occur during interleaved execution, particularly with uncommitted data.
Types of conflicts include Overwriting Uncommitted Data, often represented as WW Conflicts.

Lock-Based Concurrency Control

Strict Two-phase Locking Protocol (Strict 2PL):
- Requires obtaining a shared (S) lock before reading and an exclusive (X) lock before writing.
- Locks are released only when the transaction completes.
- No other transaction can obtain any lock on an object held under an exclusive lock.
- Ensures only serializable schedules.

Aborting a Transaction

When a transaction (Ti) is aborted, all its changes must be undone.
If another transaction (Tj) reads data last written by Ti, Tj also must be aborted to maintain consistency.
Systems typically prevent cascading aborts by keeping locks until a transaction commits.
Transactions can only read data written by another transaction after the latter commits.

Logging Mechanism

A log records every write action of a transaction to facilitate rollback and system recovery.
Log entries for writes include both the old and new values.
Commit and abort actions of transactions are also recorded in the log.
Log records must first be written to disk before changes to the actual data.

Log Structure and Recovery

Log records are linked by transaction IDs, simplifying the undo process.
Logs are often duplicated and stored in stable storage for reliability.
Aries Recovery Algorithm Phases:
- Analysis Phase: Scans the log from the last checkpoint to identify active transactions and dirty pages.
- Redo Phase: Reapplies updates to dirty pages in the buffer pool to ensure data consistency.

Description

Explore the intricacies of transaction management in Database Management Systems with a focus on anomalies that occur from interleaved execution. This quiz covers concepts such as overwriting uncommitted data and the strict two-phase locking protocol. Test your understanding of these critical mechanisms in ensuring data consistency and integrity.