Thursday, 6 July 2017

What are the different strategies for placing the data in distributed database

What are the different strategies for placing the data in distributed database?, different data allocation metrics followed in distributed database, how data are placed in a distributed database?


Different strategies for placing data in distributed database


A distributed database implementation follows one of the following data placement strategies for ease of access. The selection is influenced by many factors like the locality, reliability, performance, storage and communication costs.

Strategy
Description
Centralized
Database tables are stored in a single location/single site (server). All the other sites have to forward the request to the central site for accessing data.
Fragmented (Partitioned)
Database tables are fragmented (either vertically or horizontally or both) and different fragments are stored in different sites.
Complete replication
Database tables are replicated (duplicated) fully into two or more copies and each copy is stored in different sites.
Selective replication
Among set of tables, certain tables are made into multiple copies and stored in different sites. The tables that are most frequently accessed will be replicated.
Hybrid
It is the mix of all. Most of the distributed databases follow this strategy. Here, some of the tables replicated, some of the tables fragmented, etc.


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