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RUM Conjecture of Database Access Method

RUM Conjecture of Database Access Method. Database Access Method. Defines how to store and access data in a database system Heap file Sorted file B+ Tree index Hash Index …. Requirements of A Good Access Method. Read optimized how much time it cost to read the data

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RUM Conjecture of Database Access Method

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  1. RUMConjectureofDatabaseAccessMethod

  2. DatabaseAccessMethod • Defineshowtostoreandaccessdatainadatabasesystem • Heapfile • Sortedfile • B+Treeindex • HashIndex • …

  3. RequirementsofAGoodAccessMethod • Readoptimized • howmuchtimeitcosttoreadthedata • e.g.,rangesearch,equalitysearch • Updateoptimized • howmuchtimeitcosttoupdatethedata • e.g.,insert,delete,update • Memory(Space)optimized • howmuchspaceitusestostorethedata • e.g.,auxiliarystructures,duplicates

  4. However… RUMConjecture • RUMConjecture:Anaccessmethodthatcanminimizetwooutoftheread,update,andmemoryoverheads,cannotoptimizethethirdoverhead! • Inotherwords,theremightnotbethe“best”accessmethodthatisoptimalforallthethreerequirements!

  5. Example:Append-OnlyLog • Readunoptimized • Asearchmayneedtoscantheentirelog • Spaceunoptimized • Whendelete/updateanentry,oldentryisnotdeletedin-place • Updateoptimized • Eachupdatesimplyappendtheentrytothelog

  6. Example:B+Tree • Readoptimized: • EachsearchonlyvisitslogB(N)pages • Updateunoptimized: • AnupdaterequiresvisitingatleastlogB(N)pages • Spaceunoptimized: • Pagesoftenarenotfull

  7. Example:HashIndex • Readoptimized: • AquerysimplychecksO(1)bucket • Updateunoptimized: • Anupdatemayneedtosplitoverflowbuckets • Spaceunoptimized: • Bucketsoftenarenotfull

  8. OtherAccessMethods

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