Download - 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
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ITM - 702 Database Management System
Types of Redundancies
Redundancy (engineering)Redundancy (information theory)Redundancy (total quality management)Data redundancy
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ITM - 702 Database Management System
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
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ITM - 702 Database Management System
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
ITM - 702 Database Management System
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.
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ITM - 702 Database Management System
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
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ITM - 702 Database Management System
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
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ITM - 702 Database Management System
1st Normal Form
Eliminate Repeating GroupsTwo-dimensional tablesAll Atomic Data itemsNo Repeating groupsDesignated Primary Key
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ITM - 702 Database Management System
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
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ITM - 702 Database Management System
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
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ITM - 702 Database Management System
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.
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ITM - 702 Database Management System
Redundancy management or fault
Fault DetectionFault DiagnosisFault ContainmentFault MaskingFault CompensationFault Repair
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ITM - 702 Database Management System
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
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ITM - 702 Database Management System
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
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ITM - 702 Database Management System
Time Redundancy
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ITM - 702 Database Management System
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
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ITM - 702 Database Management System
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
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ITM - 702 Database Management System
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
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ITM - 702 Database Management System
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
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ITM - 702 Database Management System
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
ITM - 702 Database Management System
THANK YOUfor your patience
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