Distributed Database Systems-Types of Fragmentation I.pptx

DISTRIBUTED DATABASE SYSTEMS

1. Lecture Topics Types of Fragmentation Distributed Database Systems Lecture #9 Superior College Mian Channu Distributed Database Systems

2. Distributed Design Issues Superior College Mian Channu Distributed Database Systems Horizontal fragmentation Vertical fragmentation Mixed or Hybrid fragmentation Types of Fragmentation

3. Distributed Design Issues Superior College Mian Channu Distributed Database Systems Horizontal fragmentation Horizontal fragmentation refers to the process of dividing a table horizontally by assigning each row or (a group of rows) of relation to one or more fragments. These fragments are then be assigned to different sides in the distributed system. Some of the rows or tuples of the table are placed in one system and the rest are placed in other systems. Types of Fragmentation

4. Distributed Design Issues Superior College Mian Channu Distributed Database Systems Horizontal fragmentation Types of Fragmentation

5. Distributed Design Issues Superior College Mian Channu Distributed Database Systems Horizontal fragmentation where Fi is the selection formula used to obtain fragment Ri (also called the fragmentation predicate). Note that if Fi is in conjunctive normal form, it is a minterm predicate ( mi ). Example 3.7. The decomposition of relation PROJ into horizontal fragments PROJ1 and PROJ2 in Example 3.1 is defined as follows 1 : PROJ1 = σBUDGET ≤ 200000 (PROJ) PROJ2 = σBUDGET > 200000 (PROJ) Types of Fragmentation

6. Distributed Design Issues Superior College Mian Channu Distributed Database Systems Horizontal fragmentation PROJ1 = σLOC =“Montreal” (PROJ) PROJ2 = σLOC =“New York” (PROJ) PROJ3 = σLOC =“Paris” (PROJ) Types of Fragmentation

7. Distributed Design Issues Superior College Mian Channu Distributed Database Systems Horizontal fragmentation Types of Fragmentation

8. Distributed Design Issues Superior College Mian Channu Distributed Database Systems Derived Horizontal Fragmentation A derived horizontal fragmentation is defined on a member relation of a link according to a selection operation specified on its owner. It is important to remember two points. First, the link between the owner and the member relations is defined as an equi -join. Second, an equi -join can be implemented by means of semijoins Types of Fragmentation

9. Distributed Design Issues Superior College Mian Channu Distributed Database Systems Derived Horizontal Fragmentation Types of Fragmentation where w is the maximum number of fragments that will be defined on R , and Si = σFi (S), where Fi is the formula according to which the primary horizontal fragment Si is defined.

10. Distributed Design Issues Superior College Mian Channu Distributed Database Systems Derived Horizontal Fragmentation Types of Fragmentation

11. Distributed Design Issues Superior College Mian Channu Distributed Database Systems Completeness Reconstruction Disjointness Checking for Correctness

12. Distributed Design Issues Superior College Mian Channu Distributed Database Systems Completeness The completeness of a primary horizontal fragmentation is based on the selection predicates used. As long as the selection predicates are complete, the resulting fragmentation is guaranteed to be complete as well. Since the basis of the fragmentation algorithm is a set of complete and minimal predicates, Pr ’ , completeness is guaranteed as long as no mistakes are made in defining Pr ’ Checking for Correctness

13. Distributed Design Issues Superior College Mian Channu Distributed Database Systems Reconstruction Reconstruction of a global relation from its fragments is performed by the union operator in both the primary and the derived horizontal fragmentation. Thus, for a relation R with fragmentation FR = {R1,R2,..., Rw }, Checking for Correctness

14. Distributed Design Issues Superior College Mian Channu Distributed Database Systems Disjointness In derived fragmentation, however, there is a semijoin involved that adds considerable complexity. Disjointness can be guaranteed if the join graph is simple. Otherwise, it is necessary to investigate actual tuple values. Checking for Correctness

15. Distributed Design Issues Superior College Mian Channu Distributed Database Systems The extent to which the database should be fragmented is an important decision that affects the performance of query execution. The degree of fragmentation goes from one extreme, that is, not to fragment at all, to the other extreme, to fragment to the level of individual tuples (in the case of horizontal fragmentation) or to the level of individual attributes (in the case of vertical fragmentation). Fragmentation Degree of Fragmentation

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