L23b.sp11 - Computer Science 425 Computer Science 425...

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Lecture 20-1 Lecture 20-1 Computer Science 425 Distributed Systems CS 425 / CSE 424 / ECE 428 Fall 2010 Computer Science 425 Distributed Systems CS 425 / CSE 424 / ECE 428 Fall 2010 010, I . Gupta, K. Nahrtstedt, S. Mitra, N. Vaidya, M. T. Harandi, J. Hou Indranil Gupta (Indy) October 28, 2010 Lecture 20 Replication Control II Reading: Chapter 15 (relevant parts)
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Lecture 20-2 Lecture 20-2 Transactions on Replicated Data Transactions on Replicated Data B A Client + front end B B B A A getBalance(A) Client + front end Replica managers Replica managers deposit(B,3); U T
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Lecture 20-3 Lecture 20-3 One Copy Serialization One Copy Serialization In a non-replicated system, transactions appear to be performed one at a time in some order. This is achieved by ensuring a serially equivalent interleaving of transaction operations. One-copy serializability : The effect of transactions performed by clients on replicated objects should be the same as if they had been performed one at a time on a single set of objects (i.e., 1 replica per object). Equivalent to combining serial equivalence + replication transparency/consistency
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Lecture 20-4 Lecture 20-4 Two Phase Commit Protocol For Transactions on Replicated Objects Two Phase Commit Protocol For Transactions on Replicated Objects Two level nested 2PC In the first phase, the coordinator sends the canCommit? command to the participants, each of which then passes it onto the other RMs involved (e.g., by using view synchronous communication) and collects their replies before replying to the coordinator. In the second phase, the coordinator sends the doCommit or doAbort request, which is passed onto the members of the groups of RMs.
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Lecture 20-5 Lecture 20-5 Primary Copy Replication Primary Copy Replication For now, assume no crashes/failures All the client requests are directed to a single primary RM. Concurrency control is applied at the primary. To commit a transaction, the primary communicates with the backup RMs and replies to the client. View synchronous comm. gives one-copy serializability Disadvantage? Performance is low since primary RM is bottleneck.
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Lecture 20-6 Lecture 20-6 Read One/Write All Replication Read One/Write All Replication An FE (client front end) may communicate with any RM. Every write operation must be performed at all of the RMs Each contacted RM sets a write lock on the object. A read operation can be performed at any single RM A contacted RM sets a read lock on the object. Consider pairs of conflicting operations of different transactions on the same object. Any pair of write operations will require locks at all of the RMs
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L23b.sp11 - Computer Science 425 Computer Science 425...

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