Extended altruistic locking favoring short-lived transaction in database management systems

Abstract

We can often find long-lived transactions(LLTs) in a conventional database manage systems. The chacteristics of these LLTs are large access set and long execution time. Large access sets of LLTs inevitably cause conflicts on data items with other short and more common transactions, and their long execution times bring about the delay of such conflicting transactions for long periods. Although concurrency protocols, say Altruistic Locking (AL) and Extended Altruistic Locking(XAL), have been proposed for resolving such delays of transactions, there are still a number of transactions that suffer delays caused by an LLT. In this thesis, we propose an extension to XAL, named XAL/S, for the purpose of reducing the number of short transactions that suffer delays due to conflicts on data items with LLTs and increasing the degree of concurrency. For such purpose, we introduce a new wake expansion rule to XAL, whereby short transactions can access the pre-released data items of an LLT without the restriction of AL and XAL that short transactions which wishes to access the data items preleased by an LLT have to hold their first locks on such pre-released data items. Finally, we play simulations of XAL/S and present the simulation results for the purpose of evaluating the performance of XAL/S.