2019年 Database Systems (资料库系统)ppt课件.ppt

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1、DatabaseSystems(資料庫系統)October31,2019Lecture#61Physical&DigitalSpaceInteractionConsidermovingapencil…PhysicalspacemovementmappingtodigitalspaceDigitalspacemovementmappingtophysicalspaceWhichoneismoredifficult?TheActuatedWorkbench(MITmedialab)2CourseAdm

2、inistrationAssignment#2:due11/2Assignment#3:postonthecoursehomepageDue11/8(nextTuesday)PracticumAssignment#1:Postonthecoursehomepageon11/7NextWeekReading:Chapter93ReflectionHowtodesignadatabase?Conceptualdesign:ERModelLogicaldesign:RelationalModelHowto

3、askquestionsonadatabase?RelationalAlgebra&SQLsWhat’snext?Howtogetfastaccesstorecords?Fileorganizations&indexesWhat’sfurthernext?Howtooptimizequeryprocessingtime?4OverviewofStorage&IndexingChapter85OutlineTypesofexternalstoragedevicesFileorganizationsQu

4、estions:Howtostoretablerecordsonexternalstoragedevice(e.g.,adisk)?Howtospeedupaccesstoneededrecordsonadisk?Heapfile,SortedfileIndexingdatastructuresTree-basedindexing,Hash-basedindexingComparisononfileorganizationsQuestion:whichoneisbetter/worseinperfo

5、rmance?IndexesandPerformanceQuestion:howtouseindexingforbetterperformance?6DataonExternalStorageExternalStorage:offerpersistentdatastorageUnlikephysicalmemory,datasavedonapersistentstorageisnotlostwhenthesystemshutdownsorcrashes.7TypesofExternalStorage

6、DevicesMagneticDisks:Canretrieverandompageatfixedcost~$1perGigabyteButreadingseveralconsecutivepagesismuchcheaperthanreadingtheminrandomorderTapes:Canonlyreadpagesinsequence$0.3perGigabyteCheaperthandisks;usedforarchivalstorageOthertypesofpersistentsto

7、ragedevices:Opticalstorage(CD-R,CD-RW,DVD-R,DVD-RW)Flashmemory8DefinitionArecordisatupleorarowinarelationtable.Fixed-sizerecordsorvariable-sizerecordsAfileisacollectionofrecords.Storeonetableperfile,ormultipletablesinthesamefileApageisafixedlengthblock

8、ofdatafordiskI/O.Afileisconsistedofpages.Adatapagealsocontainsacollectionofrecords.Typicalpagesizesare4and8KB.9FileOrganizationMethodofarrangingafileofrecordsonexternalstorage.Recordid(rid)isusedtolocatearecordonadisk[pageid,slotnumber]