Research On Transaction Management In Engineering Database System Supporting Cooperative Design

Engineering database system (EDBS) supporting cooperation provides the data object management for computer supported cooperative design (CSCD). Transaction management is the hardcore of the EDBS. This paper discusses several researching results on transaction management in EDBS supporting cooperation. It includes the description of cooperative activities and cooperative transaction model, the functional structure of the transaction process system in EDBS supporting cooperation, the concurrency control mechanism, the commit protocol and the recovery process. And the experiment in a prototype system based on the research above is presented as well.Given the characteristics of cooperative design environment, the description of cooperative design activities is presented. Based on the description, a cooperative transaction model is proposed. The model has a nested hierarchical structure and adopts some advantages of other transaction models, which makes it more flexible. And the model provides some interaction between two sub-transactions so that it can provide partly cooperation between design transactions.Two concurrency control methods that support cooperative design transaction are presented. In multi-granularity locking mechanism based on ordered sharing locks, we extend the simple lock mode-Shared lock(S/R Lock)/Exclusive lock(X/W Lock) by introducing several other locks. The corresponding compatible matrix is given. The locking protocol and the locking algorithms is also presented. This method can support cooperate design transaction of read and update. The other method is CBR locking mechanism based on ordered sharing locks. It is developed by considering the continuity of the serial transactions executed in a same local client. The locking protocol is presented. This method can also support some cooperation.The timeout-trigger Two-Phases Commit protocol for engineering design transaction is proposed. The principles and the fault process of the protocol are presented. On one hand, the protocol allows 'early' commit in participant transactions and 'early' commit of-n-coordinator transaction before timeout, if the finishing condition is held. On the other hand, if the coordinator can't commit after timeout comes, the coordinator can force the uncommitted participants to vote, and make final decision according to the votes.A mechanism named savepoint is also developed. The mechanism adopts redundant storage. It stores the partly design result to server during the design according to the command of users, so that it can diminish the lost of fault. It can support some cooperation through broadcast. And it can solve cascading recovery by using savepoint number (SN). A recovery algorithm based on log and savepoint mechanism is also developed. The algorithm can resolve most site fault in cooperative design and provide some selected rollback.In the end, the experiment of the multi-granularity locking mechanism based on ordered sharing locks and timeout-trigger two-phases commit protocol for engineering design transaction is executed in a prototype system. The analysis of the results are also given. The experiment proves that our thoughts are correct and feasible.