Flexible Integration of Optimistic and Pessimistic Concurrency Control in Mobile Environments
Limited execution capability, weak connections with the fixed network, frequent disconnections, and mobility dictate naturally an optimistic mode for transaction execution at mobile hosts (MH): the relevant computation is performed at MHs with cached data to provide quick response to the user, but the execution is validated against concurrent transactions and ACID properties maintained at the fixed network. Some of the proposals in the literature to reduce the likelihood of invalidation and thus increase the meaningfulness of computation at MH are: (i) If the validation fails, the transaction could be re-executed and accepted even when the results differ from the original ones but within certain limits; (ii) Validation/re-execution idea can be extended to several intermediate stages and the computation at MH adjusted with respect to changes in the database state at the fixed network. In this paper, we strengthen the computation at MH further by facilitating partial guarantee against invalidation. This is accomplished by switching the computation to a pessimistic mode. Varying degrees of pessimism are provided. They balance the guarantee against its effect on other transactions’ executions.
KeywordsMobile computing Transaction processing Concurrency control Re-execution Pessimistic mode
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