What is the difference between centralized database system and distributed database system?

Distributed Database vs Centralized Database

Centralized database is a database in which data is stored and maintained in a single location. This is the traditional approach for storing data in large enterprises. Distributed database is a database in which data is stored in storage devices that are not located in the same physical location but the database is controlled using a central Database Management System (DBMS).

What is Centralized Database?

In a centralized database, all the data of an organization is stored in a single place such as a mainframe computer or a server. Users in remote locations access the data through the Wide Area Network (WAN) using the application programs provided to access the data. The centralized database (the mainframe or the server) should be able to satisfy all the requests coming to the system, therefore could easily become a bottleneck. But since all the data reside in a single place it easier to maintain and back up data. Furthermore, it is easier to maintain data integrity, because once data is stored in a centralized database, outdated data is no longer available in other places.

What is Distributed Database?

In a distributed database, the data is stored in storage devices that are located in different physical locations. They are not attached to a common CPU but the database is controlled by a central DBMS. Users access the data in a distributed database by accessing the WAN. To keep a distributed database up to date, it uses the replication and duplication processes. The replication process identifies changes in the distributed database and applies those changes to make sure that all the distributed databases look the same. Depending on the number of distributed databases, this process could become very complex and time consuming. The duplication process identifies one database as a master database and duplicates that database. This process is not complicated as the replication process but makes sure that all the distributed databases have the same data.

What is the difference between Distributed Database and Centralized Database?

While a centralized database keeps its data in storage devices that are in a single location connected to a single CPU, a distributed database system keeps its data in storage devices that are possibly located in different geographical locations and managed using a central DBMS. A centralized database is easier to maintain and keep updated since all the data are stored in a single location. Furthermore, it is easier to maintain data integrity and avoid the requirement for data duplication. But, all the requests coming to access data are processed by a single entity such as a single mainframe, and therefore it could easily become a bottleneck. But with distributed databases, this bottleneck can be avoided since the databases are parallelized making the load balanced between several servers. But keeping the data up to date in distributed database system requires additional work, therefore increases the cost of maintenance and complexity and also requires additional software for this purpose. Furthermore, designing databases for a distributed database is more complex than the same for a centralized database.

Centralized database

In a centralized database, all data is stored and maintained in one place. The central location is a computer or database. All the data is stored in a single location for example mainframe computer.

This database mostly maintains and modify using internet connection like LAN and WAN.

The centralized database mostly used in colleges, banks, hospitals and in small companies. In a centralized database system one computer act as a server for storing whole data. In a centralized database system, client/server architecture is used it is the very simplest form of a database system in which one client sent a request to the server. The server will receive a request and will be the response. Many small organizations use a centralized database system.

In the above diagram all the data stored on a single computer. This database is known as the centralized database.

Characteristics of a Centralized System

• Presence of a global clock:

As the whole system consists of a central computer (a server/ a master) and many client computers (a computer/ a slave), all client nodes connect up with the global clock(the clock of the central node).

• One single central unit:

The central server will communicate with all clients. All client sends a request to server and server will be the response.

• Dependent failure of components:

When the server goes down all system will be destroyed. The client is not able to access the database

Advantages of  Centralized Database Management System

Some advantages of a Centralized Database Management System are:

1. The integrity of data is increased as the whole database is stored at a single physical location. In this way, it is easy to manage the data is most consistent and accurate in this way.
2. The data redundancy is controlled in a centralized database. All the data is stored in one location and it cannot distribute on different places. So, it is easier to make sure all the datastore is not duplicate. in this way redundancy easily control
3. The centralized database is much secure. Because all data is stored in one place
4. Data is easily portable because it is stored in the same place. Strong data security
5. The centralized database is inexpensive than other databases .it required less expense on maintains
6. All the information is easily accessible. it takes less time to get the required information from a centralized database

Disadvantages Centralized Database Management System

Some disadvantages of a Centralized Database Management System are:

1. If the network is slow, the accessibility of required because all data is stored in one place.Since all the data is at one location. The searching process takes much time.
2. If the centralized server fails due to some reasons all database will be a loss.
3. All data is stored in one place when many users access data at the same time to may create many problems.
4. When the many record same place will be accessed at the same time the collision will be accord in the result of collision may be precious data will be lost.

Distributed Database

In the distributed database all clients are not attached with common server computer. The data is stored on a different computer located in the same physical location. The database is distributed over the network. Collection of data can be distributed over many physical places.it improves overall performance. However, rely on a central DBMS which manages all its different storage devices remotely, as it is not necessary for them to be kept in the same physical and/or geographical location.

Characteristics Distributed or decentralized database System –

Lack of a global clock:

Every node works independently from each other, have different clocks that they run and follow.

Multiple central units (Computers/Nodes/Servers):

More than one central unit which can listen for connections from other nodes

Dependent failure of components:

One central node failure does not destroy the whole system.

Components of Distributed database System

Components of Distributed database System are,

• Node (Computer, Mobile, etc.)
• A communication link

Advantages of Decentralized System –

1. 1. The performance of the distributed database is very high because all load is divide over all nodes.
   2. All the nodes available for work, leading to high availability
   3. More autonomy and control over resources .because each node controls its own work, it has better autonomy leading to more control over resources

Disadvantages of Decentralized System –

1. It is very difficult to use because it is very large and complex.
2. When one node becomes fail it is very difficult to detect because there are many nodes and responsible for their own behavior
3. The server accepts request from nodes in the system but it is actually difficult to find out which node indeed served the request.

Comparison of Distributed and Centralized Database System