We are Using Coin Mining Also To Monitise This Website. If you keep this website open for some time that helps us to keep making content for you.

The Eduladder is a community of students, teachers, and programmers just interested to make you pass any exams. So we help you to solve your academic and programming questions fast.
In eduladder you can Ask,Answer,Listen,Earn and Download Questions and Question papers.
Watch related videos of your favorite subject.
Connect with students from different parts of the world.
Apply or Post Jobs, Courses ,Internships and Volunteering opportunity. For FREE
See Our team
Wondering how we keep quality?
Got unsolved questions? Ask Questions

Sixth-Semester-BE-Degree-Examination-JuneJuly-2013-Compiler-Design-Question-paper-->View question

Asked On2017-12-18 11:00:23 by:leo

Taged users:


Be first to dislike this question
Talk about this  Like  Dislike
View all qusetions
The design issues of Distributed Database

Distributed Database Design

• One of the main questions that are being addressed is how database and the applications that run against it should be placed across the sites.
• There are two basic alternatives to placing data: partitioned (or no-replicated) and replicated.
• In the partitioned scheme, the database is divided into a number of disjoint partitions each of which is placed at the different site. Replicated designs can be either fully replicated (also called fully duplicated) where entire database is stored at each site, or partially replicated (or partially duplicated) where each partition of the database is stored at more than one site, but not at all the sites.
• The two fundamental design issues are fragmentation, the separation of the database into partitions called fragments, and distribution, the optimum distribution of fragments. The research in this area mostly involves mathematical programming in order to minimize the combined cost of storing the database, processing transactions against it, and message communication among site.

Distributed Directory Management

• A directory contains information (such as descriptions and locations) about data items in the database. Problems related to directory management are similar in nature to the database placement problem discussed in the preceding section.

• A directory may be global to the entire DDBS or local to each site; it can be centralized at one site or distributed over several sites; there can be a single copy or multiple copies.
Distributed Query Processing
• Query processing deals with designing algorithms that analyze queries and convert them into a series of data manipulation operations. The problem is how to decide on a strategy for executing each query over the network in the most cost-effective way, however, the cost is defined.
• The factors to be considered are the distribution of data, communication cost, and lack of sufficient locally-available information. The objective is to optimize where the inherent parallelism is used to improve the performance of executing the transaction, subject to the abovementioned constraints.

Distributed Concurrency Control
• Concurrency control involves the synchronization of access to the distributed database, such that the integrity of the database is maintained. It is, without any doubt, one of the most extensively studied problems in the DBMS field.
• The concurrency control problem in a distributed context is somewhat different than in a centralized framework. One not only has to worry about the integrity of a single database, but also about the consistency of multiple copies of the database. The condition that requires all values of multiple copies of every data item to converge to the same value is called mutual consistency.
• Let us only mention that the two general classes are pessimistic, synchronizing the execution of the user request before the execution starts, and optimistic, executing requests and then checking if the execution has compromised the consistency of the database.
• Two fundamental primitives that can be used with both approaches are locking, which is based on the mutual exclusion of access to data items, and time-stamping, where transactions executions are ordered based on timestamps.
• There are variations of these schemes as well as hybrid algorithms that attempt to combine the two basic mechanisms.

Distributed Deadlock Management
• The deadlock problem in DDBSs is similar in nature to that encountered in operating systems.
• The competition among users for access to a set of resources (data, in this case) can result in a deadlock if the synchronization mechanism is based on locking. The well-known alternatives of prevention, avoidance, and detection/recovery also apply to DDBSs.

Reliability of Distributed DBMS
• It is important that mechanisms be provided to ensure the consistency of the database as well as to detect failures and recover from them. The implication for DDBSs is that when a failure occurs and various sites become either inoperable or inaccessible, the databases at the operational sites remain consistent and up to date.
• Furthermore, when the computer system or network recovers from the failure, the DDBSs should be able to recover and bring the databases to the failed sites up-to-date. This may be especially difficult in the case of network partitioning, where the sites are divided into two or more groups with no communication among them.

• If the distributed database is (partially or fully) replicated, it is necessary to implement protocols that ensure the consistency of the replicas, i.e. copies of the same data item have the same value.
• These protocols can be eager in that they force the updates to be applied to all the replicas before the transactions complete, or they may be lazy so that the transactions update one copy (called the master) from which updates are propagated to the others after the transaction completes.

Answerd on:2017-12-15 Answerd By:Purnima

Be first to like this answer

Be first to dislike this answer
Talk about this  Like  Dislike

Stay home and watch eduladder premium videos for free In at this qurentine.

You might like this video:Watch more here

Watch more videos from this user Here

Learn how to upload a video and start earning here

Lets together make the web is a better place

We made eduladder by keeping the ideology of building a supermarket of all the educational material available under one roof. We are doing it with the help of individual contributors like you, interns and employees. So the resources you are looking for can be easily available and accessible also with the freedom of remix reuse and reshare our content under the terms of creative commons license with attribution required close.

You can also contribute to our vision of "Helping student to pass any exams" with these.
Answer a question: You can answer the questions not yet answered in eduladder.How to answer a question
Career: Work or do your internship with us.Work with us
Create a video: You can teach anything and everything each video should be less than five minutes should cover the idea less than five min.How to upload a video on eduladder