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Information RedundancyInformation can be defined a group of bits organised in a well defined manner. In real time system large amount is information has to be transferred in a very short time in a precisely secure manner. There are many casualties during the transfer of information. For example the information can be corrupted due to [...]

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Hardware Redundancy

Use of additional hardware to compensate for failures

This can be done in two ways

Fault detection, correction and Masking. Multiple hardware units may be assigned to do the same task in parallel and their results compared. If one or more units are faulty, we can express this to show up as a disagreement in the [...]

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A Fault in one part of the system cause large voltage swings in the other parts of the system. So it is necessary to prevent from spreading through the system. This is called as containment.
This can be divided into

Fault Containment Zone (FCZ) and

A failure of some part of the computer outside an FCZ cannot cause [...]

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Fault Tolerance Techniques

Introduction

Hardware Faults – Occurs due to a physical defect of a system like a broken wire or a logic struck at 0 in a gate.
Software faults – occurs due to a bug introduced in a system so the software misbehaves for a given set of inputs
Error – the manifestation of a fault is [...]

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Databases for real time systems are meant for the use of both hard and soft systems. Since hard real time systems needs strict timing constraints, conventional disk based databases are not suitable, but soft real time systems makes use of disk based systems through FCFS, Elevator or scan policy algorithm.
There should be some solution for [...]

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In disk based scheduling, the disks are located and traced by traversing the sectors and tracks. Tracks are concentric circles and sectors are just originating from the center of the disks.So, disk scheduling algorithms are slower when compared with the memory based scheduling. Under disk based schedulingTa=Tw+Tp+TtTa is the access timeTw is the time spent [...]

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Pessimistic Concurrency Control

The transactions are been checking for violating the serialization consistency before letting it execute is called pessimistic concurrency control

Two phase locking Scheme

Read /Write lock as a phase
Unlock – another phase
Both the above phases wont interleave, because of this, there may be deadlock, which can be detected by means of deadlock [...]

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Transaction Abortions
Transaction abortion is of two types, either

Termination abortion or

The Transaction which is aborted in this way won’t be restarted
Example: An attempt to divide by zero error

Non Termination Abortion

The transaction which will be restarted after it is being aborted
Example: data conflict due to a deadlock, If two transactions are involved in a deadlock, [...]

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Transaction Priorities

Transactions are granted access to the processors based on their priorities.
All the transactions in the real time DB are associated with a deadline, hence Earliest Deadline First (EDF) algorithm finds a greater solution to schedule those transactions. But EDF algorithm will be working efficiently if the number of transactions are moderate. But usually [...]

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Main Memory Databases

The entire database is residing on the main memory is the concept behind main memory databases. But there are some problems like data backups and storing logs. So Main memory databases are to rely on Disk based systems to store logs and backups.
General purpose databases are really huge to sit in to [...]

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