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1、AdaptiveWebCachingPrincipleInvestigators:LixiaZhang(UCLA),SallyFloydandVanJacobson(LBNL)February,1997.Technicalrationale,technicalapproach,andconstruc-tiveplanThesuccessoftheWorldWideWebhasbroughtanexponentialgrowthoftheuserpopu-lation,thetotalhostcount,andtheamount
2、oftotaltracvolumeontheInternet.AstheInternetconnectivityisreachingtheglobalcommunity,theWorldWideWebisbecomingaglobal-scaledatadisseminationsystem.Inevitably,thisover-nightexponentialgrowthhasalsocausedtracoverloadatvariousplacesinthenetwork.Untilrecently,advances
3、indeliveryfabricsgavetheimpressionthatscalingtheInternetwassimplyanissueofaddingmoreresources.Bandwidthandprocessingpowercouldbebroughttowheretheywereneeded.TheInternet'sexponentialgrowth,however,exposedthisimpressionasamyth.Informationaccesshasnotbeen,norwillitlike
4、lybe,evenlydistributed.Ashavebeenrepeatedobserved,popularWebpagescreatehotspots"ofnetworkload,withthesamedatatransmittedoverthesamenetworklinksagainandagaintothousandsofdi erentusers.Hot-spotsalsomovearound.ThephotographsofVenuscongestedLosNettosforoneweek theMidn
5、ightMadness"releaseofMicrosoft'sInternetExplorer3.0congestedNorth-WestNetfor48hours,threateningInternetconnectivitytoUniversityofWashingtonThesearebutacoupleofwellpublicizedexamples.RecentstudiesbyMargoSeltzerofHarvardUniversityalsocon rmsthat
ash-crowdsareverycommo
6、n,andthatthecoolsiteoftheday"movesaround[6].BottleneckhotspotsdevelopandbreakupmorequicklythanthenetworkortheWebserverscanbere-provisioned.Abruteforceapproachtoprovisioningisnotonlyinfeasible,butalsoine ective.Thelessonsoftwenty- veyearsofInternetexperienceteachust
7、hatcachingistheonlywaytohandletheexponentialgrowthofuserdemands.Seltzer'sstudyalsoshowsthatthemorepopularthepages,thelesslikelytheyaretochange.Similarly,thelargerdocumentsarelesslikelytochangethansmallerones.Insteadofalwaysfetchingpagesfromtheoriginatingsource,datar
8、equestscanoftenbemoree ectivelyansweredby ndinglocal"copiesnearconsumers.Weneedtodevelopanewinfrastructurefordatadisseminationonanever-in
