A Progressive Reprocessing Transaction Model for Updating Spatial Data in Mobile Computing Environments

Abstract

Mobile transactions for updating spatial data are long-lived transactions that update local copies of the mobile platforms on disconnection. Since a mobile transaction is physically separated from its global transaction, the concurrent updates of mobile transactions should be merged into the global database after committing. Validation-based schemes, which are well-known to be appropriate for mobile transactions, have the overhead of aborting long duration transactions that conflict with some transactions. It is definitely unacceptable to cancel all the updates of a long-lived transaction due to conflicts with just a few objects. This paper introduces a novel reprocessing-transaction model that handles update conflicts between mobile transactions without aborting. Instead of aborting mobile transactions that conflict with committed transactions, the proposed model executes a new subtransaction called a reprocessing transaction, which reexecutes exactly the conflicted operations on conflicted objects with foreign conflicted objects. Foreign conflicted objects are part of the data committed by the other concurrent transactions and are related to the conflicted objects. We also propose a progressive reprocessing scheme to allow the non-conflicted objects of a mobile transaction to be incrementally exposed to other concurrent transactions in order to reduce the starvation of reprocessing transactions. Our reprocessing transaction model has the benefit of being able to serialize mobile transactions without aborting or waiting.