The Distributed Database System Must Be _____ of the Computer Hardware System.
A distributed database is a database in which storage devices are not all attached to a common processing unit such as the CPU, [1] controlled by a distributed database management system (together sometimes called a distributed database organisation). Information technology may be stored in multiple computers, located in the same physical location; or may be dispersed over a network of interconnected computers. Different parallel systems, in which the processors are tightly coupled and plant a single database organization, a distributed database system consists of loosely coupled sites that share no physical components.
Collections of data (east.g. in a database) tin can be distributed across multiple physical locations. A distributed database tin reside on network servers on the Internet, on corporate intranets or extranets, or on other visitor networks. The replication and distribution of databases improves database functioning at end-user worksites. [ii] [ clarification needed ]
To ensure that the distributive databases are up to appointment and current, there are two processes: replication and duplication. Replication involves using specialized software that looks for changes in the distributive database. In one case the changes have been identified, the replication procedure makes all the databases await the same. The replication procedure can be circuitous and fourth dimension consuming depending on the size and number of the distributive databases. This process tin also require a lot of fourth dimension and computer resource. Duplication on the other hand is not as complicated. It basically identifies one database as a master and then duplicates that database. The duplication process is unremarkably done at a gear up time later hours. This is to ensure that each distributed location has the same information. In the duplication process, changes to the main database but are allowed. This is to ensure that local information volition not be overwritten. Both of the processes tin keep the data current in all distributive locations. [2]
Besides distributed database replication and fragmentation, there are many other distributed database design technologies. For example, local autonomy, synchronous and asynchronous distributed database technologies. These technologies' implementation can and does depend on the needs of the business and the sensitivity/confidentiality of the data to be stored in the database, and hence the cost the business is willing to spend on ensuring information security, consistency and integrity.
Contents
- 1 Architecture
- 1.1 Homogeneous DDBMS
- one.2 Heterogeneous DDBMS
- 2 Important considerations
- 3 Advantages
- four Disadvantages
- 5 Run across as well
- 6 References
Compages
A database user accesses the distributed database through:
- Local applications
- applications which do not require data from other sites.
- Global applications
- applications which do require data from other sites.
A homogeneous distributed database has identical software and hardware running all databases instances, and may announced through a single interface equally if it were a unmarried database. A heterogeneous distributed database may have dissimilar hardware, operating systems, database direction systems, and fifty-fifty data models for different databases.
Homogeneous DDBMS
In a homogeneous distributed database all sites have identical software and are enlightened of each other and concur to cooperate in processing user requests. Each site surrenders part of its autonomy in terms of correct to change schema or software. A homogeneous DDBMS appears to the user as a single organisation. The homogeneous system is much easier to design and manage. The following weather condition must exist satisfied for homogeneous database:
- The operating system used, at each location must be same or compatible.[ co-ordinate to whom? ] [ farther caption needed ]
- The information structures used at each location must be same or compatible.
- The database application (or DBMS) used at each location must be same or uniform.
Heterogeneous DDBMS
In a heterogeneous distributed database different sites may use unlike schema and software. Difference in schema is a major problem for query processing and transaction processing. Sites may not be aware of each other and may provide only limited facilities for cooperation in transaction processing. In heterogeneous systems, different nodes may have different hardware & software and data structures at various nodes or locations are also incompatible. Different computers and operating systems, database applications or data models may be used at each of the locations. For instance, one location may have the latest relational database direction technology, while another location may shop information using conventional files or former version of database management system. Similarly, one location may take the Windows NT operating system, while some other may take UNIX. Heterogeneous systems are usually used when individual sites use their own hardware and software. On heterogeneous system, translations are required to let advice betwixt different sites (or DBMS). In this organisation, the users must be able to brand requests in a database language at their local sites. Usually the SQL database language is used for this purpose. If the hardware is different, so the translation is straightforward, in which computer codes and word-length is changed. The heterogeneous arrangement is often not technically or economically feasible. In this organisation, a user at 1 location may be able to read merely not update the data at another location.
Important considerations
Intendance with a distributed database must be taken to ensure the following:
- The distribution is transparent — users must be able to interact with the system equally if information technology were one logical system. This applies to the arrangement'due south functioning, and methods of access amidst other things.
- Transactions are transparent — each transaction must maintain database integrity across multiple databases. Transactions must besides be divided into sub-transactions, each sub-transaction affecting 1 database system.
There are mainly two approaches to store a relation r in a distributed database system:
- A) Replication
- B) Fragmentation/Segmentation
A) Replication: In replication, the system maintains several identical replicas of the same relation r in dissimilar sites.
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- Data is more bachelor in this scheme.
- Parallelism is increased when read request is served.
- Increases overhead on update operations every bit each site containing the replica needed to be updated in order to maintain consistency.
- Multi-datacenter replication provides geographical diversity: http://basho.com/tag/multi-datacenter-replication/
B) Fragmentation: The relation r is fragmented into several relations rane, r2, r3....rdue north in such a style that the bodily relation could be reconstructed from the fragments and so the fragments are scattered to dissimilar locations. In that location are basically ii schemes of fragmentation:
-
- Horizontal fragmentation - splits the relation by assigning each tuple of r to one or more fragments.
- Vertical fragmentation - splits the relation by decomposing the schema R of relation r.
Advantages
- Management of distributed data with different levels of transparency like network transparency, fragmentation transparency, replication transparency, etc.
- Increment reliability and availability.
- Easier expansion.
- Reflects organizational construction — database fragments are located in the departments they relate to.
- Local autonomy or site autonomy — a department can control the data about them (every bit they are the ones familiar with it.)
- Protection of valuable data — if there were ever a catastrophic event such as a burn down, all of the information would non be in one place, but distributed in multiple locations.
- Improved performance — data is located near the site of greatest demand, and the database systems themselves are parallelized, allowing load on the databases to be counterbalanced among servers. (A high load on i module of the database won't bear on other modules of the database in a distributed database.)
- Economics — information technology costs less to create a network of smaller computers with the power of a single large computer.
- Modularity — systems can be modified, added and removed from the distributed database without affecting other modules (systems).
- Reliable transactions - Due to replication of database.
- Hardware, Operating System, Network, Fragmentation, DBMS, Replication and Location Independence.
- Continuous functioning, fifty-fifty if some nodes go offline (depending on design).
- Distributed query processing can ameliorate performance.
- Distributed transaction direction.
Single site failure does not affect performance of system. All transactions follow A.C.I.D. belongings: A-atomicity, the transaction takes identify as a whole or not at all; C-consistency, maps 1 consistent DB country to some other; I-isolation, each transaction sees a consistent DB; D-durability, the results of a transaction must survive organization failures. The Merge Replication Method is popularly used to consolidate the data betwixt databases.
Disadvantages
- Complexity — extra work must be done by the DBAs to ensure that the distributed nature of the system is transparent. Extra work must as well be done to maintain multiple disparate systems, instead of one big one. Extra database design piece of work must also be washed to account for the disconnected nature of the database — for example, joins become prohibitively expensive when performed across multiple systems.
- Economics — increased complexity and a more extensive infrastructure means extra labour costs.
- Security — remote database fragments must be secured, and they are non centralized so the remote sites must be secured every bit well. The infrastructure must also be secured (e.g., by encrypting the network links betwixt remote sites).
- Difficult to maintain integrity — merely in a distributed database, enforcing integrity over a network may crave as well much of the network's resources to be feasible.,
- Inexperience — distributed databases are difficult to work with, and as a immature field there is not much readily bachelor experience on proper practice.
- Lack of standards — there are no tools or methodologies yet to help users convert a centralized DBMS into a distributed DBMS.
- Database design more complex — besides of the normal difficulties, the design of a distributed database has to consider fragmentation of data, allocation of fragments to specific sites and data replication.
- Additional software is required.
- Operating Organisation should support distributed environment.
- Concurrency command: it is a major event. Information technology can exist solved by locking and timestamping.
- Distributed access to data
- Analysis of distributed data
Come across likewise
- Centralized database
- Data grid
- Distributed data store
- Distributed cache
- Distributed database direction system
- Routing protocol
References
- ^
This article incorporates public domain material from the General Services Administration certificate "Federal Standard 1037C".
- ^ a b O'Brien, J. & Marakas, Thou.M.(2008) Management Information Systems (pp. 185-189). New York, NY: McGraw-Colina Irwin
- M. T. Özsu and P. Valduriez, Principles of Distributed Databases (tertiary edition) (2011), Springer, ISBN 978-1-4419-8833-1
- Elmasri and Navathe, Fundamentals of database systems (third edition), Addison-Wesley Longman, ISBN 0-201-54263-3
- Oracle Database Administrator'south Guide 10g (Release 1), http://docs.oracle.com/cd/B14117_01/server.101/b10739/ds_concepts.htm
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