earticle

영어

An efficient functionality of any distributed database system “DDBS” is highly dependent on its proper design in terms of the adopted fragmentation and allocation methods. However, an optimal fragmentation and allocation design techniques could be very complex and requires good experiences and knowledge to reach. Fragmentation of a large, global databases are performed by dividing the database relations horizontally, vertically or as a combination of both. In order to enable distributed database systems to work efficiently, these fragments have to be allocated across the available sites in such a way that reduces communication cost i.e. to minimize the total volume of data transmitted during queries execution over sites. This paper presents a new data re-allocation model for replicated and non-replicated constrained DDBSs by bringing a change to data access pattern. This approach assumes that the distribution of fragments over network sites was initially performed according to a properly forecasted set of query frequency values that could be employed over sites. Our model takes sites constraints into account in the re-allocation phase. It proposes an efficient plan to re-allocate data fragments across sites based on communication and update cost values for each fragment individually. The re-allocation process will be performed by selecting the maximal update cost value for each fragment and making the re-allocation accordingly. Experimental results confirmed that the proposed technique will effectively contribute in solving fragments re-allocation problem in a dynamic distributed relational databases environment.