Abstract
Extended transaction models in databases were motivated by the need of complex applications such as CAD/CAM and software engineering. Nested transaction models have so far been shown to play an important role in such applications. However, these models are not yet fully studied. In this paper, we focus on the applicability of such models to real-time database systems, particularly to issues related to the global serializability of distributed real-time nested transactions. Our contribution in this field is twofold: we propose (i) a real-time concurrency control, called 2PL-NT-HP, to solve data conflicts problem between nested transactions and (ii) a real-time commit protocol to guarantee the uniform commitment of distributed nested transactions. To this purpose, we have adapted the PROMPT real-time commit protocol which is designed specifically for the real-time flat transactions. This protocol causes intra-aborts cascade in nested environment and hence decreases its real-time performances. To alleviates this drawback, the borrowing subtransaction carries out a speculative execution by accessing both before and after-image of the lending subtransaction. Simulations we have carried out show that S-PROMPT approach is very useful in DRTDBSs compared to the classical approaches.
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