《分布式系统原理与范型》课后习题与答案(英文)
SOLUTIONSTOCHAPTER1PROBLEMS1.Q:Whatistheroleofmiddlewareinadistributedsystem?
A:Toenhancethedistributiontransparencythatismissinginnetworkoperat-ingsystems.Inotherwords,middlewareaimsatimprovingthesingle-systemviewthatadistributedsystemshouldhave.2.Q:Explainwhatismeantby(distribution)transparency,andgiveexamplesofdifferenttypesoftransparency.
A:Distributiontransparencyisthephenomenonbywhichdistributionaspectsinasystemarehiddenfromusersandapplications.Examplesincludeaccesstransparency,locationtransparency,migrationtransparency,relocationtran-sparency,replicationtransparency,concurrencytransparency,failuretran-sparency,andpersistencetransparency.3.Q:Whyisitsometimessohardtohidetheoccurrenceandrecoveryfromfailuresinadistributedsystem?
A:Itisgenerallyimpossibletodetectwhetheraserverisactuallydown,orthatitissimplyslowinresponding.Consequently,asystemmayhavetoreportthataserviceisnotavailable,although,infact,theserverisjustslow.4.Q:Whyisitnotalwaysagoodideatoaimatimplementingthehighestdegreeoftransparencypossible?
A:Aimingatthehighestdegreeoftransparencymayleadtoaconsiderablelossofperformancethatusersarenotwillingtoaccept.5.Q:Whatisanopendistributedsystemandwhatbenefitsdoesopennesspro-vide?
A:Anopendistributedsystemoffersservicesaccordingtoclearlydefinedrules.Anopensystemiscapableofeasilyinteroperatingwithotheropensys-temsbutalsoallowsapplicationstobeeasilyportedbetweendifferentimple-mentationsofthesamesystem.6.Q:Describepreciselywhatismeantbyascalablesystem.
A:Asystemisscalablewithrespecttoeitheritsnumberofcomponents,geo-graphicalsize,ornumberandsizeofadministrativedomains,ifitcangrowinoneormoreofthesedimensionswithoutanunacceptablelossofperfor-mance.7.Q:Scalabilitycanbeachievedbyapplyingdifferenttechniques.Whatarethesetechniques?
A:Scalingcanbeachievedthroughdistribution,replication,andcaching.
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