A Transaction Model to Improve Data Availability in Mobile Computing

In this project, we incorporate a prewrite operation before a write operation in a mobile transaction to improve data availability. A prewrite operation does not update the state of a data object but only makes visible the value that the data object will have after the commit of the transaction. Once a transaction read all the values and declares all the prewrites, it can pre-commit at mobile host (i.e., computer connected to unreliable mobile communication network). The remaining transaction’s execution is shifted to the stationary host (i.e., to the computer connected to the reliable fixed network). Writes on database take time and consume resources at stationary host and are therefore, delayed. This reduces network traffic congestion. Since the expensive part of the transaction execution is shifted to the stationary host, it also reduces the computing expenses at mobile host. A pre-committed transaction’s prewrite values are made visible both at mobile and stationary hosts before the final commit of the transaction. Thus, increases data availability during frequent disconnection common in mobile computing. Since a pre-committed transaction does not abort, no undo recovery needs to be performed in our model. A mobile host can cache only prewrite values of the data objects, which will take less memory, transmission time, energy and can be transmitted over low bandwidth. We have analysed various cases of running transactions concurrently both at mobile and stationary hosts. We have also discussed the locking algorithm for our model and proved that our algorithm produces only serializable schedules.

Resercher

Dr. Sanjay Madria