chapter14 - Chapter 14: Replication Introduction System...

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Introduction System model and group communication Fault-tolerant services Highly available services Transactions with replicated data Summary Chapter 14: Replication
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Replication is a key technology to enhance service Performance enhancement Example caches in DNS servers replicated web servers Load-balance Proximity-based response Replication for distributed service
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Increase availability Factors that affect availability Server failures Network partitions Replication for distributed service … continued
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Introduction System model and group communication Fault-tolerant services Highly available services Transactions with replicated data Summary Chapter 14: Replication
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A basic architectural model Replica manager One replica manager per replica Receive FE’s request, apply operations to its replicas atomically Front end One front end per client Receive client’s request, communicate with RM by message passing System model
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Request The front end issues the request to one or more replica managers Coordination The replica managers coordinate in preparation for executing the request consistently Different ordering Execution The replica managers execute the request (perhaps tentatively) An operation executed on a replicated object
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Agreement The replica managers reach consensus on the effect of the request Response One or more replica managers responds to the front end An operation executed on the replicated object (2)
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Multicast in a dynamic group Processes may join and leave the group as the system executes A group membership service Manage the dynamic membership of groups Multicast communication An example Group communication
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Provide an interface for group membership changes Create and destroy process groups Add or withdraw a process to or from a group Implement a failure detector Mark processes as suspected or unsuspected No messages will be delivered to the suspected process It excludes a process from a membership if it is suspected to have failed or to have become un reachable Role of the group membership service
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Notify members of group membership changes Group view : a list of identifiers of all active processes in the order of join Perform group address expansion A process multicast a message addressed by a group identifier rather than a list of processes Role of the group membership service (2)
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Group view The lists of the current group members Deliver a view when a membership change occurs, the application is notified of the new membership Group management service delivers to any member View delivery
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Order If a process p delivers view v ( g ) and then view v’ ( g ),then no other process q p delivers v’ ( g ) before v ( g ) Integrity If process p delivers view v(g) then p v(g)
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chapter14 - Chapter 14: Replication Introduction System...

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