Robert Edward Gruber. Optimistic Concurrency Control For Nested Distributed Transactions. Master's thesis, MIT, June 1989. 109  Home/Search   Document Details and Download   Summary   Related Articles   Check

....to require less additional messages. We believe that a distributed method, similar to some distributed deadlock detection protocol, can also be devised. 7.2. 4 Optimistic Model Work can be done on using disconnected actions in a model that uses optimistic concurrency control, like the one in [Gruber 1989]. The optimistic approach allows atomic action to execute without synchronization (e.g. block when another action uses a needed object) and rely on commit time validation to ensure serialization of the actions. Optimistic methods are useful when things are not likely to go wrong , since they ....

Robert Edward Gruber. Optimistic Concurrency Control For Nested Distributed Transactions. Master's thesis, MIT, June 1989. 109

....server scheme for serial and parallel validation is generalized to a distributed system 15 in [Ceri82] Haerder [Haerder84] has developed the notion of forward and backward validation. Optimistic schemes have also been extended to exploit the semantics of abstract data types [Herlihy90] Gruber [Gruber89] has suggested validation based optimistic schemes for the nested transaction model. A system implementation that caches objects and uses a classic optimistic scheme is Servio Logic s Gemstone [Maier86] Gemstone is a distributed system that allows multiple clients but objects can be stored at ....

....Reed [Reed83] describes a timestamping strategy for serializing transactions in this model. Systems such as Argus [Liskov84] and Camelot [Spector87] provide a computational model that supports nested transactions using pessimistic locking. An optimistic scheme for this model has been presented in [Gruber89]. To simplify the transaction model, Thor does not support nested transactions. 1.1.2 The Commit Process When a client commits a transaction, the system has to ensure that all servers agree on committing or aborting the transaction. This effect is usually achieved with the help of a 2 phase ....

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Gruber R. E. Optimistic Concurrency Control for Nested Distributed Transactions. S.M. thesis, Massachusetts Institute of Technology, 1989.

....and later Kung and Robinson [KR81] suggested the idea of using optimism for concurrency control. Since then a number of optimistic schemes have been discussed in the literature. Other distributed schemes achieve a global serialization order using atomic multicast [RT90] or logical clocks [ABGS87, Gru89] Atomic multicast adds additional per message overhead, while logical clocks must be explicitly managed as part of the two phase commit, complicating the algorithm. Our use of loosely synchronized clocks avoids all these problems; more importantly, it also allows us to make time dependent ....

R. Gruber. Optimistic Concurrency Control for Nested Distributed Transactions. Technical Report MIT/LCS/TR-453, MIT Laboratory for Computer Science, Cambridge, MA, 1989.

....to moderate contention between user transactions. The scheme uses timestamps generated from local clocks to define the serial order of transactions; we assume clocks are loosely synchronized, which is the case in networks today [24] This approach is simpler and cheaper than previous techniques [2, 6, 14, 25]; other techniques are discussed in Section 3.6. More importantly, timestamps allow us to truncate transaction history and still avoid spurious aborts. By reading its local clock, a server can estimate the range of timestamps of transactions that are likely to request a commit there; only ....

....et al. 8] and later Kung and Robinson [18] suggested the idea of using optimism for concurrency control. Since then a number of optimistic schemes have been discussed in the literature. Other distributed schemes achieve a global serialization order using atomic multicast [25] or logical clocks [2, 14]. Atomic multicast adds additional per message overhead, while logical clocks must be explicitly managed as part of the two phase commit, complicating the algorithm. The scheme described in [6] used the following approach: To validate a transaction T, a participant computes the set of other ....

R. E. Gruber. Optimistic Concurrency Control for Nested Distributed Transactions. Tech. Report MIT/LCS/TR-453, MIT Laboratory for Computer Science, June 1989.

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