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 |