Distributed DBMSPage 5. 1 © 1998 M. Tamer Özsu & Patrick Valduriez Outline Introduction Background Distributed DBMS Architecture  Distributed Database Design à Fragmentation à Data Location Distributed Query Processing (Briefly) Distributed Transaction Management (Extensive) n Building Distributed Database Systems (RAID) Mobile Database Systems Privacy, Trust, and Authentication Peer to Peer Systems

Distributed DBMSPage 5. 2 © 1998 M. Tamer Özsu & Patrick Valduriez 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 DBMSPage 5. 3 © 1998 M. Tamer Özsu & Patrick Valduriez Dimensions of the Problem Level of sharing Level of knowledge Access pattern behavior partial information dynamic static data data + program complete information

Distributed DBMSPage 5. 4 © 1998 M. Tamer Özsu & Patrick Valduriez 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 DBMSPage 5. 5 © 1998 M. Tamer Özsu & Patrick Valduriez Distribution Design Issues Why fragment at all? How to fragment? How much to fragment? How to test correctness? How to allocate? Information requirements?

Distributed DBMSPage 5. 6 © 1998 M. Tamer Özsu & Patrick Valduriez 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 DBMSPage 5. 7 © 1998 M. Tamer Özsu & Patrick Valduriez PROJ 1 :projects with budgets less than $200,000 PROJ 2 :projects with budgets greater than or equal to $200,000 PROJ 1 PNOPNAMEBUDGET LOC P3CAD/CAM250000New York P4Maintenance310000Paris P5CAD/CAM500000Boston PNOPNAME LOC P1Instrumentation150000Montreal P2Database Develop New York BUDGET PROJ 2 Fragmentation Alternatives – Horizontal New York PROJ PNOPNAMEBUDGETLOC P1Instrumentation150000Montreal P3CAD/CAM P2Database Develop P4Maintenance310000Paris P5CAD/CAM500000Boston New York

Distributed DBMSPage 5. 8 © 1998 M. Tamer Özsu & Patrick Valduriez Fragmentation Alternatives – Vertical PROJ 1 :information about project budgets PROJ 2 :information about project names and locations PNOBUDGET P P P P P PNOPNAMELOC P1InstrumentationMontreal P3CAD/CAMNew York P2Database Develop.New York P4MaintenanceParis P5CAD/CAMBoston PROJ 1 PROJ 2 New York PROJ PNOPNAMEBUDGETLOC P1Instrumentation150000Montreal P3CAD/CAM P2Database Develop P4Maintenance310000Paris P5CAD/CAM500000Boston New York

Distributed DBMSPage 5. 9 © 1998 M. Tamer Özsu & Patrick Valduriez Degree of Fragmentation Finding the suitable level of partitioning within this range tuples or attributes relations finite number of alternatives

Distributed DBMSPage © 1998 M. Tamer Özsu & Patrick Valduriez Completeness à Decomposition of relation R into fragments R 1, R 2,..., R n is complete if and only if each data item in R can also be found in some R i Reconstruction  If relation R is decomposed into fragments R 1, R 2,..., R n, then there should exist some relational operator  such that R =  1≤ i ≤ n R i  Disjointness à If relation R is decomposed into fragments R 1, R 2,..., R n, and data item d i is in R j, then d i should not be in any other fragment R k ( k ≠ j ). Correctness of Fragmentation

Distributed DBMSPage © 1998 M. Tamer Özsu & Patrick Valduriez Other Fragmentation Issues Privacy Security Bandwidth of Connection Reliability Replication Consistency Local User Needs