William Easton

Introduction  Mobile Environments  Locking and Data Starvation  Mobile DB Architecture  Timing Mechanisms  Static Timer  Dynamic Timer  Preemptive Timer

Mobile Environments  Prone to Connection loss Timeouts Loss of bandwidth Reduced storage Limited battery power All these contribute to the frequency of failures of mobile databases.

Data Starvation  Phone connects and locks data Phone disconnects Phone holds that lock (indefinitely) Other mobile devices cannot access that information  These locking strategies are good for traditional databases but are not optimal for mobile

Mobile DB Architecture  Mobile host  Fixed host  Mobile host may not always be connected to the fixed host

Timing Mechanisms  Static timer A transaction must commit before the timer is finished ○ If not the transaction is aborted and locked data is aquired by the next mobile host attempting to access the information  Dynamic Timer The solution this paper introduces

Dynamic Timer  Starts off with specified timer  As transactions are executed it changes according to how they are being executed  If transactions are running past the timer and are rolled back then the timer is increased slightly

Dynamic Timer  So processes that would’ve unsuccessfully processed earlier might be able to be completed Leads to fewer rollbacks There has to be a catch ○ Larger overhead ○ Processes in the queue will have to wait longer to access the data they need  There is a threshold time that the dynamic timer cannot surpass

Dynamic Timer This is an activity diagram from the paper to depict how the timer will be adjusted.

Static Timer

Dynamic Timer

Preemptive Timer

Final Metrics  Timeout(static)  Dynamic  Preemption  Overall the preemptive has the best commit rate with the least time but does require the knowledge of execution times

Questions  Mobile environments  Static methods  Dynamic method  Preemptive method  Conclusions