CORNELL CS 632 - Distributed Database Systems (38 pages)

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Distributed Database Systems



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Distributed Database Systems

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Pages:
38
School:
Cornell University
Course:
Cs 632 - Database Systems

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Distributed Database Systems R Optimizer Validation and Performance Evaluation for Local Queries R Optimizer Validation and Performance Evaluation for Distributed Queries Lothar F Mackert Guy M Lohman Lothar F Mackert Guy M Lohman R An Overview of the Architecture R Williams D Daniels L Haas G Lapis B Lindsay P Ng R Obermarck P Selinger A Walker P Wilms and R Yost What is System R R System R is a database system built as a research project at IBM San Jose Research now IBM Almaden Research Center in the 1970 s System R introduced the SQL language and also demonstrated that a relational system could provide good transaction processing performance R basic facts Each site is autonomous as possible No central scheduler no central deadlock detection no central catalog etc R uses snapshot data a copy of a relation s in which the data is consistent but not necessarily up to date used to provide a static copy of the database Object naming in R For autonomy no global naming system required To keep object names unique site name incorporated into names called System Wide Names SWN EX USER USER SITE OBJECT NAME BIRTH SITE Global Catalogs in R All Global Table names stored at all sites Creation of a global table involves broadcasting global relation name to all sites in the network Catalogs at each site keep and maintain info about objects in the dbase including replicas or fragments stored at the site Transaction Numbering A transaction is given a number that is composed of the unique site name and a unique sequence number from that site that incorporates time of day at that site so no synchronization between sites is needed The transaction number is both unique and ordered in the R framework Transaction Numbering cont Numbers used in deadlock detection Uniqueness is used for identification purposes to determine which transactions control which locks to avoid case where a transaction is waiting for itself In case of a deadlock R aborts the youngest largest numbered transaction



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