Commit-order oriented validation scheme for transaction scheduling in mobile distributed database systems: COOV

In this paper, we propose a new transaction numbering scheme and a new validation scheme for controlling transactions optimistically in client-server architectural mobile distributed database systems (MDDBSs). In the system, mobile units (MUs) request transaction-related services, e.g., concurrency control. commit process, then the mobile support stations (MSSs) provide the required sen-ices. The mobile computing environment makes it very difficult for each MU to assign unique transaction number to transactions since it is allowed to move in communication disconnected states. Besides, validating transactions numbered by the previous transaction numbering theme could wait indefinitely in the case of data transfer delay Thus, we propose a new transaction numbering scheme called data-transfer time oriented transaction numbering scheme (DATTO). in which we can remove waiting time for validation by determining validation-start time with data-transfer completion time. However, if the previous validation scheme for the static environment is directly applied transactions numbered by DATTO, undesirable results could occur in abnormal cases due to latency on the wireless communication. Thus, we also propose a neu validation scheme, called commit-order oriented validation (COOV), which is always able to produce correct results by applying backward validation to the abnormal cases.