Fazal rafi.. database concurancy control and recovery
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This document discusses database recovery and concurrency control. It covers backup facilities that create periodic backups of the entire database. Checkpoint facilities synchronize the database and transaction logs, allowing recovery from a short period rather than reprocessing the entire day. The document also discusses concurrency control techniques like pessimistic and optimistic approaches to manage simultaneous transactions and ensure serializability. Locking mechanisms are the most common way of achieving serialization and include different locking levels like database, table, page and record.
Fazal rafi.. database concurancy control and recovery
- 1. © Copyright 2008 STI - INNSBRUCK www.sti-innsbruck.at Presentation of Advance Database on Concurrenccy Control & DB Recovery Designed and Prepared by Rafi Uah & Fazli Mola Jan
- 2. Chapter 12 © 2007 by Prentice Hall 2 Database Recovery Mechanism for restoring a database quickly and accurately after loss or damage Recovery facilities: • Backup Facilities • Journalizing Facilities • Checkpoint Facility • Recovery Manager
- 3. Chapter 12 © 2007 by Prentice Hall 3 Back-up Facilities Automatic dump facility that produces backup copy of the entire database Periodic backup (e.g. nightly, weekly) Backups stored in secure, off-site location
- 4. Chapter 12 © 2007 by Prentice Hall 4 Checkpoint Facilities DBMS periodically refuses to accept new transactions system is in a quiet simple Database and transaction logs are synchronized This allows recovery manager to resume processing from short period, instead of repeating entire day
- 5. Chapter 12 © 2007 by Prentice Hall 5 Concurrency Control Problem–in a multiuser environment, simultaneous access to data can result in interference and data loss Solution–Concurrency Control The process of managing simultaneous operations against a database so that data integrity is maintained and the operations do not interfere with each other in a multi- user environment
- 6. Chapter 12 © 2007 by Prentice Hall 6 Concurrency Control Process of managing simultaneous execution of transactions in a shared database, to ensure the serializability of transactions, is known as concurrency control.
- 7. Chapter 12 © 2007 by Prentice Hall 7 Concurrency Control Techniques Pessimistic concurrency control Optimistic concurrency control
- 8. Chapter 12 © 2007 by Prentice Hall 8 Pessimistic Concurrency Control • Pessimistic Concurrency Control assumes that conflicts will happen • Pessimistic Concurrency Control techniques detect conflicts as soon as they occur and resolve them using blocking.
- 9. Chapter 12 © 2007 by Prentice Hall 9 Optimistic Concurrency Control • Optimistic Concurrency Control assumes that conflicts between transactions are rare. • Does not require locking • Transaction executed without restrictions
- 10. Chapter 12 © 2007 by Prentice Hall 10 Concurrency Control Techniques Serializability Finish one transaction before starting another Locking Mechanisms The most common way of achieving serialization Data that is retrieved for the purpose of updating is locked for the updater No other user can perform update until unlocked
- 11. Chapter 12 © 2007 by Prentice Hall 11 Locking Mechanisms Locking level: Database–The entire database is locked and become unavailable to other users.This is used during the backup of the entire Database. Table–The entire Table containing a requested record is locked Page–very commonly used Record–only the requested row is locked; fairly commonly used Field–only particular field or column is locked; impractical
- 12. Chapter 12 © 2007 by Prentice Hall 12 Locking Mechanisms Types of locks: Shared lock–Read but no update permitted. Exclusive lock–No access permitted. Used when preparing to update
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