HAADAS : An enhanced approach for Re- allocation of Fragments in Peer-to-Peer Distributed Databases Dr. D.I. George Amalarethinam Director-MCA, Associate Professor Department of Computer Science Jamal Mohamed College (Autonomous) Tiruchirappalli, India di_george@ymail.edu Dr. C. Balakrishnan Assistant Professor Alagappa Institute of Skill Development Alagappa University Karaikudi, India balasjc@gmail.com Abstract- The process of allocating fragments into the appropriate sites is a NP-Complete problem in nature. It is a crucial step in the design of Pee-to-Peer Distributed Databases. This paper proposes a methodology for fragment re-allocation by using Assignment algorithm of optimization principle, namely, Hungarian Assignment Algorithm based Data Allocation Strategy (HAADAS). The objective of the work is to reduce the number of un-successful queries that are forwarded to other sites of the network. The effective allocation of fragments directly influences the efficiency in executing the user queries. The simulation results confirms that the re-allocation of fragments in suitable sites is influencing the communication cost while transaction. Keywords: ElasticPeerDB, Peer-to-Peer databases, fragmentation, allocation, optimization technique I. INTRODUCTION The characteristics of Distributed data processing provide an efficient way of improving the performance, reliability, availability and modularity. Adhering with this idea, the Distributed Database System (DDBS) is a collection of multiple, logically interrelated databases distributed over a computer network [1]. There will be a possibility of improved response times to queries and upgrading system capacity or performance incrementally. The conceptually simplest distribution scheme is to distribute at the table level: any given table is stored in its entirety at some site or it may be partitioned as logical units and stored in different sites, this technique is called as Fragmentation and Allocation. These fragments contain sufficient information to allow reconstruction of the original relation. Fragmentation is desirable for performance reasons. There are horizontal, vertical and mixed or hybrid fragmentations. The horizontal fragment is a subset of the tuples with all attributes in that relation. Horizontal fragmentation splits the relation „horizontally‟ by assigning each tuple or group (subset) of tuples of a relation to one or more fragments, where each tuple or subset has a certain logical meaning. Vertical fragmentation splits the relation by decomposing „vertically‟ by columns (attributes). It requires to include the primary key (candidate key) attributes in every fragment so that the full relation can be reconstructed from the fragments. In vertical fragmentation, system-provided „tuple- ID‟ (or TID) is used as the primary key attribute along with stored relation as address for linking tuples. Horizontal (or vertical) fragmentation of a relation, followed by further vertical (or horizontal) fragmentation of the same fragments, is called mixed fragmentation. Allocation refers the process of allocating fragment or each copy of a fragment into a particular site of the distributed system. Fragment placement strategies may be centralized, partitioned or fragmented and replicated. The replication of fragments helps to improve availability, performance of retrieval of global queries and reliability. Peer-to-Peer (P2P) Database has distinction characteristic to the client-server model. Each node of the network would act as both client and as well as server, towards requesting data from nearby nodes, routing, transporting and serving data to other nodes. The characteristics of P2P technology makes suitable for storing multiple copies of data in several nodes, to offer reliable access of data and to distribute the load of requests. These features of P2P technology promise a network which is dynamic, reliable and scalable. The Peer-to-Peer concept having the potential to handle the data in an effectual manner. This paper explains a cluster based architecture for Distributed Databases, namely, ElasticPeerDB. This addresses the fragmentation and allocation phases in database design. ElasticPeerDB considers the works done on the predicate based fragmentation and introduced the clustering approach to draft the database model. This paper proposes an optimized strategy for allocating the data among the sites. The paper is organized as follows. The section II presents literature reviews on fragmentation, allocation, clustering. Section III describes the ElasticPeerDB architecture and allocation strategy. In Section IV an improved allocation methodology is presented. The Section V describes the simulation results of the new methodology. Finally Section VI give conclusion and future research guidelines. II. LITERATURE REVIEW Bellatreche et al., [2] made a study on horizontal fragmentation in the object-oriented model. Huang and Chen International Journal of Applied Engineering Research, ISSN 0973-4562 Vol. 10 No.82 (2015) © Research India Publications; httpwww.ripublication.comijaer.htm 315