Istituto di Scienza e Tecnologie dell'Informazione     
Thanos C., Carlesi C., Bertino E. Performance evaluation of two concurrency control mechanisms in a distributed database system. In: Third Conference of the European Cooperation in Informatics (Munich, 1981). Proceedings, pp. 266 - 279. (Lecture Notes in Computer Science, vol. 123). 1981.
Concurrency control (CC) mechanisms are an essential component of a distributed database management system (DDBMS). Particular attention has thus been paid to these mechanisms by researchers and there have been many different proposals for synchronization algorithms. At the present, however, there is a need for an accurate evaluation to measure the impact that these algorithms have had on DDBMS performance. The studies conducted so far appear to be incomplete. This is because these studies have been restricted to an evaluation of the CC mechanisms independently of the DDBMS within which they must operate and upon which their performance obviously has considerable impact. In addition, the hypotheses assumed have been over-simplified (full redundancy, only updating operations, practically inexistent access path conflicts) /1,2,3,4,5/ and without taking into consideration the application environment i.e., the transaction characteristics (application profile). We feel that this last omissione is of particular importance as we are convinced that no one CC mechanism is capable of performing efficiently in all application environments; different algorithms are needed to satisfy different application requirements. Therefore, in our opinion, the behaviour and impact of the different CC mechanisms on DDBMS performance must be investigated with respect to specific application classes. The results of a study of this type could provide useful information for the DDBMS designer, assisting him in the choice of the most suitable algorithm for the particular application classes the DDBMS has to support. In this paper, two CC algorithms derived from the two-phase locking i.e. the decentralised and the centralised versions are evaluated and compared with respect to various applications classes.

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