redundancy management

ITM - 702 Database Management System

Presented to Dr. Debajyoti MukhopadhyayFor DBMS coursePGDM 2009-114th Semester

Redundancy Management in DBMS

By: Ariful KayalDebal

ChaudhariPrasenjit

SenguptaRohit KrishnaVinay Asopa

1


Types of Redundancies

Redundancy (engineering)Redundancy (information theory)Redundancy (total quality management)Data redundancy

2


Redundancy (engineering)In engineering, redundancy is the duplication of

critical components of a system with the intention of increasing reliability of the system, usually in the case of a backup or fail-safe

Each duplicate component added to the system decreases the probability of system failure according to the formula:

where:n - number of componentspi - probability of component i failingp - the probability of all components failing (system

failure)3


Redundancy (information theory)

Redundancy in information theory is the number of bits used to transmit a message minus the number of bits of actual information in the message

In describing the redundancy of raw data, the rate of a source of information is the average entropy per symbol. For memory-less sources, this is merely the entropy of each symbol, while, in the most general case of a stochastic process, it is

The limit, as n goes to infinity, of the joint entropy of the first n symbols divided by n4


Redundancy (total quality management)

In total quality management, TQM, redundancy in quality or redundant quality means quality which exceeds the required quality level

Redundant quality is sometimes incorrectly used instead of even quality or constant quality, perhaps because of the positive connotations of the term redundancy used in connection with safety-critical systems.

5


Data redundancy

Data redundancy means that some data are stored twice, or that some data can be derived from other data

An advantage is that errors can be detected, and that when a data set with some redundancy is damaged, it may be possible to more or less reconstruct the original

Thus redundancy can be useful in computer data storage, and is a property of some disk arrays which provides fault tolerance, so that all or part of the data stored in the array can be recovered in the case of disk failure

6


Database Normalization

Efficiently organizing dataEliminating redundant data (for example,

storing the same data in more than one table)Ensuring data dependencies make sense (only

storing related data in a table)1st Normal Form2nd Normal Form3rd Normal Form

7


1st Normal Form

Eliminate Repeating GroupsTwo-dimensional tablesAll Atomic Data itemsNo Repeating groupsDesignated Primary Key

8


2nd Normal Form

Eliminate Redundant DataAtomic data itemsNo repeating groupsDesignated primary key (no duplicated rows)Non-primary key attributes fully functionally

dependant on the whole primary key

9


3rd Normal Form

Eliminate Columns not dependent on KeysAll-atomic data itemsNon-primary key attributes fully functionally

dependant on the whole primary keyTransitive dependencies are removed

10


Redundancy Management

Fault tolerance is sometimes called redundancy management

redundancy is the provision of functional capabilities that would be unnecessary in a fault-free environment

Redundancy is necessary, but not sufficient for fault tolerance

Redundancy management marshals the non-faulty resources to provide the correct result.

11


Redundancy management or fault

Fault DetectionFault DiagnosisFault ContainmentFault MaskingFault CompensationFault Repair

12


Coverage

The measure of success of redundancy management or fault tolerance is coverage

coverage is the probability of a system failure given that a fault occurs

The usual model is a Markov process

13


Space Redundancy

Space redundancy provides separate physical copies of a resource, function, or data item

It is effective when dealing with persistent faults, such as permanent component failures

Space redundancy is also the approach of choice when fault masking is required

The major concern in managing space redundancy is the elimination of failures caused by a fault to a function or resource that is common to all of the space-redundant units

14


Time Redundancy

15


Clocks

Many fault tolerance mechanisms, employing either space redundancy or time redundancy, rely on an accurate source of time

Probably no hardware feature has a greater effect on fault tolerance mechanisms than a clock

Multiple-processor system designers must decide to provide a fault tolerant global clock service that maintains a consistent source of time throughout the system, or to resolve time conflicts on an ad-hoc basis

16


Fault Containment Regions

Fault containment regions attempt to prevent the propagation of data faults by limiting the amount of communication between regions to carefully monitored messages and the propagation of resource faults by eliminating shared resources

In some ultra-dependable designs, each fault containment region contains one or more physically and electrically isolated processors, memories, power supplies, clocks, and communication links

Data fault propagation is inhibited by locating redundant copies of critical programs in different fault containment regions and by accepting data from other copies only if multiple copies independently produce the same result

17


Common Mode Failures

System failures occur when faults propagate to the outer boundary of the system

The goal of fault tolerance is to intercept the propagation of faults so that failure does not occur

A common-mode failure results from a single fault (or fault set)

Computer systems are vulnerable to common-mode resource failures if they rely on a single source of power, cooling, or I/O

18


Encoding

Low-level encoding decisions are made by memory and processor designers when they select the error detection and correction mechanisms for memories and data-buses

Long-haul communication facilities even provide for a negotiated fall-back in transmission speed to cope with noisy environments

These facilities should be supplemented with high-level encoding techniques that record critical system values using unique patterns that are unlikely to be randomly created

19


Sources

http://en.wikipedia.org/wiki/Database_management_system

http://www.databasedev.co.uk/database_normalization_process.html

http://en.wikipedia.org/wiki/Database_normalization

http://databases.about.com/od/specificproducts/a/normalization.htm20









http://databases.about.com/od/specificproducts/a/normalization.htm




THANK YOUfor your patience

21

redundancy management

Documents