General Architecture

Existing transaction management techniques in the Mobile MultiDataBase (MMDB) environment do not address two key issues.  First, the techniques do not address the Isolation property of global transactions.  It is difficult to enforce the Isolation property in MMDBs due to the large number of dispersed databases in the federation.  Second, they fail to address disconnection that represents catastrophic failures.

In this project, we have proposed a Pre-Serialization (PS) technique for MMDBs.  This technique allows site-transactions to commit independently so that resources may be released in a timely manner.  Two new states, Disconnected and Suspended, are introduced to fully address disconnection and migration.  A toggle operation is used to minimize the ill effects of the prolonged execution due to disconnection of mobile transactions.  A Partial Global Serialization Graph (PGSG) commit algorithm that enforces a wide range of correctness criterion with respect to the Atomicity and Isolation properties has been proposed and its correctness has been proven.  This algorithm is ideally suited for the MMDB environment as it is de-centralized, and does not require the cooperation of all sites.  We have also developed an analytical model to compare PS with other mobile transaction management techniques.  We have concluded that for very little additional overhead, the PS technique offers substantial benefits over existing techniques such as fully supporting disconnection and verifying Isolation.  Currently, we are developing a simulation model for further analysis.

MANET Environment

Supporting database transaction services in an ad-hoc mobile network raises new issues.  If a mobile host (MH) stores a database, then other MHs will try to submit transactions and get data from it.  Since both the user and the data source will be moving in this environment, finding a route from one MH to another is necessary before submitting a transaction.  Moreover, applications like battlefields are time-critical, which require their transactions to be executed not only correctly but also within their deadlines.  Thus, the Transaction Manager at the MH where the database is stored has to consider the mobility of the requesting MHs as well as the deadlines of the transactions.   Another important issue in ad-hoc networks is power or energy restriction on MHs because MHs are not connected to direct power supplies, and many of them will run on small and low-power devices.  So, energy-efficient solutions are needed for this environment.

The objective our project is to provide a solution for transaction management of mobile databases in an ad-hoc environment considering all the issues we have mentioned.  Currently, we have proposed such a solution, and built a simulation model to analyze its performance.

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