Database Recovery

This section explores database recovery techniques, focusing on mechanisms that ensure data integrity and availability despite various failure types.

Failure Classification: Understanding What Can Go Wrong

This section categorizes various types of failures in database systems and explains their implications on data integrity and recovery.

Transaction Failures

Transaction failures occur when a single executing transaction cannot complete successfully, leading to a rollback or termination.

System Crashes (Software And Hardware Failures)

This section discusses the implications and recovery strategies associated with system crashes due to software or hardware failures in database management systems.

Disk Failures (Media Failures)

Disk failures are critical failures that involve the loss of non-volatile storage, impacting database integrity and requiring complex recovery strategies.

Recovery Concepts: Log-Based Recovery (Undo/redo Logging)

Log-based recovery is essential for maintaining database integrity in the face of failures by utilizing transaction logs to undo incomplete transactions and redo committed transactions.

The Transaction Log (Journal)

This section covers the role and structure of the transaction log in a database recovery system, emphasizing its importance in maintaining durability and atomicity.

Undo Logging

Undo logging enables a database management system to reverse the effects of uncommitted or failed transactions.

Redo Logging

Redo logging is a recovery technique in database systems focused on reapplying changes from committed transactions after a failure.

Undo/redo Logging (Combined Approach)

This section discusses the combined Undo/Redo logging approach used by modern Database Management Systems (DBMS) for efficient recovery of transactions.

Checkpoints

Checkpoints in database systems are mechanisms that help optimize recovery processes by marking points of consistency, thus reducing recovery time and log processing.

Purpose Of Checkpoints

Checkpoints are essential mechanisms in database systems that significantly reduce recovery time and log processing after a system crash.

How Checkpoints Work (Simplified)

Checkpoints are crucial mechanisms in database management systems that allow for efficient recovery by synchronizing in-memory data with persistent data on disk.

Types Of Checkpoints

This section outlines the different types of checkpoints used in database management systems to streamline recovery processes after a failure.

Checkpoints In Recovery

Checkpoints are crucial mechanisms in database recovery that enhance efficiency by marking consistent states in the transaction log.

Shadow Paging

Shadow paging is a recovery technique that provides atomicity and durability by maintaining shadow copies of database pages and directories.

Basic Concept

Shadow paging provides a technique for maintaining atomicity and durability by using a backup page structure.

Commit Operation

The commit operation in shadow paging is crucial for achieving atomicity and durability by atomically switching database pointers between shadow and current page tables once a transaction is completed.

Recovery From Failures

This section focuses on the recovery techniques for handling failures in database transactions, emphasizing atomicity and durability in different scenarios.

Advantages Of Shadow Paging

Shadow paging offers a simple recovery mechanism for databases by utilizing separate page tables to manage changes, ensuring atomicity and durability.

Disadvantages Of Shadow Paging

Shadow paging has several significant disadvantages, including garbage collection overhead, performance impacts, concurrency control challenges, fragmentation, and limitations concerning media recovery.

Media Recovery

Media recovery addresses the restoration of databases following catastrophic failures impacting non-volatile storage, requiring a backup strategy for data recovery.

The Role Of Backups

Backups are essential for media recovery, providing a way to restore databases to a stable state after failures.

The Media Recovery Process (Restore And Roll Forward)

The media recovery process involves restoring a database to its state before a media failure and rolling forward with changes from transaction logs.

Key Components For Media Recovery

This section outlines the critical components required for effective media recovery in database systems, focusing on backup strategies, archived redo logs, and log sequencing.

Aries Recovery Algorithm (Brief Overview)

ARIES is a robust recovery algorithm used in DBMSs, ensuring durability and atomicity by employing log-based recovery techniques and sophisticated checkpointing.

Key Principles Of Aries

The ARIES algorithm incorporates key principles of database recovery, including Write-Ahead Logging, No-Force policy, and Steal policy, ensuring efficient handling of various failure types.

The Three Passes Of Aries Recovery After A System Crash

The ARIES recovery algorithm utilizes a three-pass approach to efficiently recover from system crashes.

Aries And Media Recovery

ARIES is a sophisticated recovery algorithm that efficiently handles crashes and media failures in database systems through a structured multi-pass recovery process and integration with backup procedures.