Deferred locking with shadow transaction for client–server DBMSs

Data-shipping systems that allow inter-transaction caching raise the need of a transactional cache consistency maintenance (CCM) protocol because each client is able to cache a portion of the database dynamically. Deferred locking (DL) is a new CCM scheme that is capable of reducing the communication overhead required for cache consistency checking. Due to its low communication overhead, DL could show a superior performance, but it tends to exhibit a high ratio of transaction abort. To cope with this drawback, we develop a new notion of shadow transaction, which is a backup-purpose one that is kept ready to replace an aborted transaction. This notion and the locking mechanism of DL have been incorporated into deferred locking with shadow transaction. Using a distributed database simulation model, we evaluate the performance of the proposed schemes under a wide range of workloads.