IntroductionOverviewBusiness RequirementsData DistributionReplicationArchitecturesSlide 7Stages of an ActionOrdering coordination typesPowerPoint PresentationRisk AnalysisFailure ModesFigure 14.11 Available copiesNetwork failure modesNode failure modesDistributed Shared MemorySlide 17Slide 18Principles of DSMConcepts & protocolsConsistency ModelsDistributed Data Base SystemArchitecture ConceptsStandard modelsControlEngineering ConcernsBandwidth Analyses & ControlDebugging Distributed Data SystemsHomeworkChoicesThe End03 December 2002 (Gary McKee) ECEN 5053 Engineering Distributed Systems 1Introduction•Lecture originally prepared by: Gary McKee–Lecturer in Computer Science at CU Boulder–Independent Consultant for 14 years–Working in the software industry for over thirty years–Currently working as a Principal Engineer (in algorithm design) for a systems engineering company in Colorado Springs•Today’s topic: Distributed Data –Reading assignment for today•Chapter 15 in Coulouris text – Replication•Chapter 18 in Coulouris text – Distributed Shared Memory (DSM)–Optional Homework•See “handout” on web site03 December 2002 (Gary McKee) ECEN 5053 Engineering Distributed Systems 2Overview•The topics to be presented:–Data Distribution–Risk Analysis–Distributed Shared Memory–Distributed Data Base Systems–Engineering Concerns–Homework: Characterizing Distributed Data Architectures03 December 2002 (Gary McKee) ECEN 5053 Engineering Distributed Systems 3Business Requirements•‘Data Distribution’ is about putting the data for a system in the correct location based on the needs of the business.•The best technology in the world is useless if:–it is not applied APPROPRIATELY–It isn’t what the customer NEEDS–It isn’t what the customer ASKED for•Carefully examine the requirements associated with a particular problem.–develop understanding of the ‘Business goals’–talk to the customerThis is NOT what I asked for, I don’t care WHAT the requirements said!!03 December 2002 (Gary McKee) ECEN 5053 Engineering Distributed Systems 4Data Distribution•What can we accomplish with the correct selection of technology for Data Distribution?–fault tolerance – hardware & software failures are not catastrophic–high availability – downtime is short, infrequent, not disruptive–Reduction of bandwidth consumption – a shared resource•There are a number of ways to accomplish data distribution in computer based systems–Replication (passive data systems)–Distributed shared memory (passive data systems)–Distributed data bases (active data systems)03 December 2002 (Gary McKee) ECEN 5053 Engineering Distributed Systems 5Replication•There are a number of ways to accomplish data distribution in computer based systems using data replication•Passive replication - this is the most traditional approach and is fairly easy to design, implement, and manage–distinguished replica, primary backup•Active replication - this approach is more robust –but at the cost of more effort in design and implementation and significantly more bandwidth consumption–multicast to all replicas03 December 2002 (Gary McKee) ECEN 5053 Engineering Distributed Systems 6Architectures•Criteria–Correctness–sequential consistency•The interleaved sequence provides a single correct copy of the objects•Program order is sustained–Linearizability•The interleaved sequence provides a single correct copy of the objects•The order of operations is consistent with the real times of the operation or request.•Effect is same as serialized operations from a single replica manager despite of order of arrival•Examples (gossip, bayou, coda)03 December 2002 (Gary McKee) ECEN 5053 Engineering Distributed Systems 7Architectures•Criteria–Correctness–sequential consistency•The interleaved sequence provides a single correct copy of the objects•Program order is sustained–Linearizability•The interleaved sequence provides a single correct copy of the objects•The order of operations is consistent with the real times of the operation or request.•Effect is same as serialized operations from a single replica manager despite of order of arrival•Examples (gossip, bayou, coda)03 December 2002 (Gary McKee) ECEN 5053 Engineering Distributed Systems 8Stages of an Action •The stages of an action are these:–Request–Coordination: FIFO, causal, total ordering–Execution–Agreement–Response03 December 2002 (Gary McKee) ECEN 5053 Engineering Distributed Systems 9Ordering coordination types•FIFO–If a front end issues request r then r’, then any correct replica manager that handles r’ handles r before it.•Causal–If the issue of request r happened-before the issues of request r’, then any correct replica manager that handles r’ handles r before it.•Total–If a correct replica manager handles r before request r’, then any correct replica manager that handles r’ handles r before it03 December 2002 (Gary McKee) ECEN 5053 Engineering Distributed Systems 10userrequestto RM7 which multicasts toRM6RM43RM97coordinationagreementexecution(bandwidth concerns are here)response03 December 2002 (Gary McKee) ECEN 5053 Engineering Distributed Systems 11Risk Analysis•What are the effects of various failure modes?–Consider the needs of the business and the cost of failure•Analytical principles–What can fail? For how long?•Transaction failure modes–Network, node, software, security–Transient, permanent–Accidental, malicious03 December 2002 (Gary McKee) ECEN 5053 Engineering Distributed Systems 12Failure Modes•Network –transient –partitioning –disconnected –corrupt/attacked •Node–transient –corrupt –dead03 December 2002 (Gary McKee) ECEN 5053 Engineering Distributed Systems 13Figure 14.11Available copiesAXClient + front endPBClient + front endReplica managersdeposit(A,3);UTdeposit(B,3);getBalance(B)getBalance(A)Replica managersYMBNABfrom text by Coulouris et al03 December 2002 (Gary McKee) ECEN 5053 Engineering Distributed Systems 14Network failure modes•transient –short time interval–temporary partitioning•partitioning –some neighbors–some nodes not available•disconnected –no neighbors•corrupt/attacked –network is unreliable–dangerous to accessnode failurenetwork failure03 December 2002 (Gary McKee) ECEN 5053 Engineering Distributed Systems 15Node failure modes•transient –data