分布式系统的复制与容错ppt课件.ppt

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1、ParallelandDistributedSystemsInstructor:ZhangWeizhe(张伟哲)ComputerNetworkandInformationSecurityTechniqueResearchCenter,SchoolofComputerScienceandTechnology,HarbinInstituteofTechnologyChapter14:ReplicationandFaultToleranceFault-tolerantservicesReplicationservicesHighlyavailableservicesSummaryOutline3F

2、aultToleranceBasicConceptsBeingfaulttolerantisstronglyrelatedtowhatarecalleddependablesystemsDependabilityimpliesthefollowing:AvailabilityReliabilitySafetyMaintainability4FailureModelsDifferenttypesoffailures.5FailureMaskingbyRedundancyFigure8-2.Triplemodularredundancy.6FlatGroupsversusHierarchical

3、Groups(a)Communicationinaflatgroup.(b)Communicationinasimplehierarchicalgroup.7AgreementinFaultySystems(1)TheByzantineagreementproblemforthreenonfaultyandonefaultyprocess.(a)Eachprocesssendstheirvaluetotheothers.8AgreementinFaultySystems(2)TheByzantineagreementproblemforthreenonfaultyandonefault

4、yprocess.(b)Thevectorsthateachprocessassemblesbasedon(a).(c)Thevectorsthateachprocessreceivesinstep3.9AgreementinFaultySystems(3)nowwithtwocorrectprocessandonefaultyprocess.mfaultyprocessonlyifatleast2m+1correctprocess!!!!10RPCSemanticsinthePresenceofFailuresFivedifferentclassesoffailuresthatcanoc

5、curinRPCsystems:Theclientisunabletolocatetheserver.Therequestmessagefromtheclienttotheserverislost.Theservercrashesafterreceivingarequest.Thereplymessagefromtheservertotheclientislost.Theclientcrashesaftersendingarequest.11BasicReliable-MulticastingSchemesAsimplesolutiontoreliablemulticastingwhenal

6、lreceiversareknownandareassumednottofail.(a)Messagetransmission.(b)Reportingfeedback.12NonhierarchicalFeedbackControlSeveralreceivershavescheduledarequestforretransmission,butthefirstretransmissionrequestleadstothesuppressionofothers.13HierarchicalFeedbackControlTheessenceofhierarchicalreliablemul

7、ticasting.Eachlocalcoordinatorforwardsthemessagetoitschildrenandlaterhandlesretransmissionrequests.14Fault-tolerantservicesReplicationservicesHighlyavailableservicesSummaryOutline15ReplicationBasicConceptsR