Abstract
Fragmentation is a design technique widely used in multimedia databases, because it produces substantial benefits in reducing response times, causing lower execution costs in each operation performed. Multimedia databases include data whose main characteristic is their large size, therefore, database administrators face a challenge of great importance, since they must contemplate the different qualities of non-trivial data. These databases over time undergo changes in their access patterns. Different fragmentation techniques presented in related studies show adequate workflows, however, some do not contemplate changes in access patterns. This paper aims to provide an in-depth review of the literature related to dynamic fragmentation of multimedia databases, to identify the main challenges, technologies employed, types of fragmentation used, and characteristics of the cost model. This review provides valuable information for database administrators by showing essential characteristics to perform proper fragmentation and to improve the performance of fragmentation schemes. The reduction of costs in fragmentation methods is one of the most desired main properties. To fulfill this objective, the works include cost models, covering different qualities. In this analysis, a set of characteristics used in the cost models of each work is presented to facilitate the creation of a new cost model including the most used qualities. In addition, different data sets or reference points used in the testing stage of each work analyzed are presented.
Highlights
Database fragmentation is a process for reducing irrelevant data accesses by grouping data frequently accessed together in dedicated segments [1]
It is observed that fragmentation methods proposed in [32,56,73] present simple cost models for their implementation. [32,56] carry out a dynamic vertical and horizontal fragmentation respectively
The three mentioned works present, for vertical, horizontal, and hybrid fragmentation, excellent ways to carry out fragmentation and are considered in a special way in this work, since they stand out for various characteristics, i.e., easy implementation, they provide a cost model, completeness, they consider multimedia data to obtain the fragmentation scheme and they take into account dynamic fragmentation
Summary
Database fragmentation is a process for reducing irrelevant data accesses by grouping data frequently accessed together in dedicated segments [1]. Entropy 2020, 22, 1352 horizontal fragmentation (HF), vertical fragmentation (VF), and hybrid or mixed fragmentation (MF) These techniques have been extended for multimedia databases [1,6]. The database elements (attributes and/or tuples) are assigned to a fragment only once at creation time, their locations are never changed. This approach has the following problems: The database administrator (DBA) has to observe the system for a significant amount of time before the partitioning operation can take place until the probabilities of queries accessing certain database elements and their frequencies are collected, this is called an analysis stage
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