we prepared this for class presentaion

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

13. 13