Cloud Database

Databases are repositories for information with links within the information that help make the data searchable [10]. A cloud database is a database that typically runs on a cloud computing platform, such as Amazon EC2, GoGrid and Rackspace. There are two common deployment models: users can run databases on the cloud independently, using a virtual machine image, or they can purchase access to a database service, maintained by a cloud database provider. Of the databases available on the cloud, some are SQL-based and some use a NoSQL data model. Distributed databases like Amazon’s SimpleDB, spread information among physically dispersed hardwae.But to the client, the information seems to be located at one place.

The advantages of such a database include the following:

- Improved Availability: If there is a fault in one database system, it will only affect one fragment of the information, not the entire database.

- Improved performance: Data is located near the site with the greatest demand and the database systems are parallelized, which allows the load to be balanced among the servers.

- Price: It is less expensive to create a network of smaller computers with the poour of one large one.

- Flexibility: System can be change and modified without harm to the entire database.

There are disadvantages including:

- Complexity: Database administrators have extra work to maintain the system.

- Labor costs: With added complexity comes the need for more workers on the payroll.

- Security: Database fragments must be secured and so must the sites housing the fragments.

- Integrity: It may be difficult to maintain the integrity of the database if it is too complex or changes too quickly.

- Standards: There are currently no standards to convert a centralized database into a cloud solution.

- Deployment model: There are two primary methods to run a database on the cloud:

Virtual machine Image - cloud platforms allow users to purchase virtual machine instances for a limited time [9]. It is possible to run a database on these virtual machines. Users can either upload their own machine image with a database installed on it, or use ready-made machine images that already include an optimized installation of a database. For example, Oracle provides a ready-made machine image with an installation of Oracle Database 11g Enterprise Edition on Amazon EC2.

- Database as a service: some cloud platforms offer options for using a database as a service, without physically launching a virtual machine instance for the database [12].

In this configuration, application owners do not have to install and maintain the database on their own. Instead, the database service provider takes responsibility for installing and maintaining the database, and application owners pay according to their usage. For example, Amazon Web Services provides two database services as part of its cloud offering, SimpleDB which is a NoSQL key-value store, and Amazon Relational Database Service which is an SQL-based database service with a MySQL interface.

Database management systems

Database management systems have adapted to run in cloud environments by horizontally scaling database servers and partitioning tables across them. This technique, known as sharding, allows multiple instances of database software — often MySQL software — to scale performance in a cloud environment. Rather than accessing a single, central database, applications now access one of many database instances depending on which shard contains the desired data as shown in the Figure 3.3.

Figure 3.3- Database sharding partitions database tables across multiple database management system instances, supporting large databases through horizontal scaling