Sudheer Thandu Presentation ID 13 Index What is allocation Problems related to allocation Information Requirements Allocation Methods Allocation Fragmentation Relation may be divided into a number of subrelations which are then distributed ID: 1047704
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1. CHAPTER 3DISTRIBUTED DATABASE DESIGNSudheer ThanduPresentation ID: 13
2. IndexWhat is allocation?Problems related to allocationInformation RequirementsAllocation Methods
3. AllocationFragmentation Relation may be divided into a number of sub-relations, which are then distributed.Allocation Each fragment is stored at site with “optimal” distribution.
4. Fragment allocationProblem StatementGiven F = {F1, F2, …, Fn} fragmentsS ={S1, S2, …, Sm} network sites Q = {q1, q2,…, qq} applications Find the "optimal" distribution of F to S.OptimalityMinimal costCommunication + storage + processing (read & update)Cost in terms of time (usually)PerformanceResponse time and/or throughputConstraintsPer site constraints (storage & processing)
5. AllocationFile Allocation (FAP) vs Database Allocation (DAP):Fragments are not individual filesrelationships have to be maintainedAccess to databases is more complicatedremote file access model not applicablerelationship between allocation and query processingCost of integrity enforcement should be consideredCost of concurrency control should be considered
6. Information RequirementsDatabase Informationselectivity of fragments size of a fragment Application Informationnumber of read accesses of a query to a fragmentnumber of update accesses of query to a fragmentA matrix indicating which queries updates which fragmentsA similar matrix for retrievalsoriginating site of each query
7. Conti..Site Informationunit cost of storing data at a site unit cost of processing at a siteNetwork Informationcommunication cost/frame between two sitesframe size
8. Allocation MethodsGeneral Form min(Total Cost) subject to response time constraint storage constraint processing constraintDecision Variable xij 1 if fragment Fi is stored at site Sj 0 otherwise
9. Conti..Solution MethodsFAP is NP-completeDAP also NP-completeHeuristics based onsingle commodity warehouse location (for FAP)knapsack problembranch and bound techniquesnetwork flow
10. Benefits Attempts to reduce the solution spaceassume all candidate partitioning known; select the “best” partitioningignore replication at firstsliding window on fragments
11.