Outline Introduction Background Distributed DBMS Architecture Distributed Database
Outline Introduction Background Distributed DBMS Architecture Distributed Database Design à Fragmentation à Data Location Distributed DBMS Distributed Query Processing (Briefly) Distributed Transaction Management (Extensive) Building Distributed Database Systems (RAID) Mobile Database Systems Privacy, Trust, and Authentication Peer to Peer Systems © 1998 M. Tamer Özsu & Patrick Valduriez Page 5. 1
Design Problem In the general setting : Making decisions about the placement of data and programs across the sites of a computer network as well as possibly designing the network itself. In Distributed DBMS, the placement of applications entails à placement of the distributed DBMS software; and à placement of the applications that run on the database Distributed DBMS © 1998 M. Tamer Özsu & Patrick Valduriez Page 5. 2
Dimensions of the Problem Access pattern behavior dynamic static data partial information Level of knowledge data + program complete information Level of sharing Distributed DBMS © 1998 M. Tamer Özsu & Patrick Valduriez Page 5. 3
Distribution Design Top-down à mostly in designing systems from scratch à mostly in homogeneous systems Bottom-up à when the databases already exist at a number of sites Distributed DBMS © 1998 M. Tamer Özsu & Patrick Valduriez Page 5. 4
Distribution Design Issues Why fragment at all? How to fragment? How much to fragment? How to test correctness? How to allocate? Information requirements? Distributed DBMS © 1998 M. Tamer Özsu & Patrick Valduriez Page 5. 5
Fragmentation Can't we just distribute relations? What is a reasonable unit of distribution? à relation views are subsets of relations extra communication à fragments of relations (sub-relations) concurrent execution of a number of transactions that access different portions of a relation views that cannot be defined on a single fragment will require extra processing semantic data control (especially integrity enforcement) more difficult Distributed DBMS © 1998 M. Tamer Özsu & Patrick Valduriez Page 5. 6
Fragmentation Alternatives – Horizontal PROJ 1 : projects with budgets less than $200, 000 PROJ 2 : projects with budgets greater than or equal to $200, 000 PROJ 1 PNO P 1 P 2 P 3 P 4 P 5 PNAME BUDGET Instrumentation 150000 Database Develop. 135000 CAD/CAM 250000 Maintenance 310000 CAD/CAM 500000 LOC Montreal New York Paris Boston PROJ 2 PNAME Instrumentation BUDGET 150000 P 2 Database Develop. 135000 Distributed DBMS PNO LOC PNO PNAME BUDGET LOC Montreal P 3 CAD/CAM 250000 New York P 4 Maintenance 310000 Paris P 5 CAD/CAM 500000 Boston © 1998 M. Tamer Özsu & Patrick Valduriez Page 5. 7
Fragmentation Alternatives – Vertical PROJ 1: information about project budgets PROJ 2: information about project names and locations Distributed DBMS PNO P 1 P 2 P 3 P 4 P 5 PROJ 1 PROJ 2 PNO BUDGET PNO P 1 P 2 P 3 P 4 P 5 150000 135000 250000 310000 500000 P 1 P 2 P 3 P 4 P 5 PNAME Instrumentation 150000 Database Develop. 135000 CAD/CAM 250000 Maintenance 310000 CAD/CAM 500000 PNAME Instrumentation Database Develop. CAD/CAM Maintenance CAD/CAM © 1998 M. Tamer Özsu & Patrick Valduriez BUDGET LOC Montreal New York Paris Boston LOC Montreal New York Paris Boston Page 5. 8
Degree of Fragmentation finite number of alternatives tuples or attributes relations Finding the suitable level of partitioning within this range Distributed DBMS © 1998 M. Tamer Özsu & Patrick Valduriez Page 5. 9
Correctness of Fragmentation Completeness à Decomposition of relation R into fragments R 1, R 2, . . . , Rn is complete if and only if each data item in R can also be found in some Ri Reconstruction à If relation R is decomposed into fragments R 1, R 2, . . . , Rn, then there should exist some relational operator such that R = 1≤i≤n. Ri Disjointness à If relation R is decomposed into fragments R 1, R 2, . . . , Rn, and data item di is in Rj, then di should not be in any other fragment Rk (k ≠ j ). Distributed DBMS © 1998 M. Tamer Özsu & Patrick Valduriez Page 5. 10
Other Fragmentation Issues Privacy Security Bandwidth of Connection Reliability Replication Consistency Local User Needs Distributed DBMS © 1998 M. Tamer Özsu & Patrick Valduriez Page 5. 11
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