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Q: Distributed vs Centralized Database ( Answered,   2 Comments )
Subject: Distributed vs Centralized Database
Category: Computers > Programming
Asked by: theja-ga
List Price: $100.00
Posted: 17 Sep 2002 06:05 PDT
Expires: 17 Oct 2002 06:05 PDT
Question ID: 65945
What are the pros and cons of a distributed database verses a centralized Database?
Subject: Re: Distributed vs Centralized Database
Answered By: joseleon-ga on 17 Sep 2002 11:09 PDT
Hello, theja:
 Well, this question has been harder to answer than I expected, but
finally is here, I have focused on the features of distributed
database systems and their advantages and disadvantages over
centralized ones, here it is:
Definition of a Distributed database

"A database that consists of two or more data files located at
different sites on a computer network. Because the database is
distributed, different users can access it without interfering with
one another. However, the DBMS must periodically synchronize the
scattered databases to make sure that they all have consistent data"

Here you can find a really good text about Distributed Databases:

Scale Up in Distributed Databases

I have extracted some key phrases on Why use a distributed database
over a centralized one:

"A big advantage of distributed DBMSs over centralized ones is that of
scalability. Growth can be sustained more gracefully in a distributed

"Local autonomy is another reason for a business to implement a DDBMS.
Since the nature of today's applications usually require data in
geographic areas that are often decentralized, it often makes sense to
implement a distributed system. In this way, data can physically
reside nearest to where it is most often accessed, thus providing
users with local control of data that they interact with."

"Another reason why one might want to consider a parallel architecture
is to improve reliability and availability of the data in a scalable
system. In a distributed system, with some careful tact, it is
possible to access some, or possibly all of the data in a failure mode
if there is sufficient data replication."

Another good paper about Distributed Database Systems:

Emerging Technologies for Developing Distributed Database Systems

And here are the solutions to a test about distributed Database
Systems, very useful to say in a few words what a DDBMS is:

Distributed Database Systems - Solutions

Major features of a DDB are:
    * Data stored at a number of sites, each site logically single
    * Sites are interconnected by a network rather than a
multiprocessor configuration
    * DDB is logically a single database (although each site is a
database site)
    * DDBMS has full functionality of a DBMS
    * To the user, the distributed database system should appear
exactly like a non-distributed database system.

Advantages of distributed database systems are:
    * local autonomy (in enterprises that are distributed already)
    * improved performance (since data is stored close to where needed
and a query may be split over several sites and executed in parallel)
    * improved reliability/availability (should one site go down)
    * economics
    * expandability
    * shareability

Disadvantages of distributed database systems are:
    * complexity (greater potential for bugs in software)
    * cost (software development can be much more 
      complex and therefore costly. Also, exchange 
      of messages and additional computations 
      involve increased overheads)
    * distribution of control (no single database administrator
controls the DDB)
    * security (since the system is distributed the chances of
security lapses are greater)
    * difficult to change (since all sites have control of their own
    * lack of experience (enough experience is not available in
developing distributed systems)
Through my research I have found this book everywhere, it seems is the
reference book on this subject:

Principles of Distributed Database Systems (2nd Edition)

I hope this is the information you were looking for and don't hesitate
to request for any clarification.

Search Strategy

features "distributed database systems" -oracle -second -edition

Subject: Re: Distributed vs Centralized Database
From: unicow-ga on 18 Sep 2002 12:33 PDT
My experience has been that distributed database are much harder to
maintain and more difficult to program for. I hope you are not using
oracle. I think you should look at your network stability and the
level of programming skills your staff has before making the decision.
Subject: Re: Distributed vs Centralized Database
From: dynamo-ga on 25 Sep 2002 02:21 PDT
There are a number of different ways databases can be distributed. 

One issue that can be problamatic is keeping the distributed database
in sync.

Let's suppose someone reserves a seat on database 1. Before that
reservation can be written to database 2, someone on database 2
reserves the same seat because it is still shown as available.

This is an overly simplified example, but transactional integrity
becomes much harder as you distribute a database out.

I'd recommend you make sure have the expertise and know how to setup
the application properly so that you avoid many of the potential
pitfalls in this area. There are applications which are very suited to
DDS implementation, but it is important to recognize which those are.
DDS is not a magic solution to scalability and growth issues.

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