Optimizing fragment constraints - A performance evaluation

A principal problem with integrity constraints' use for monitoring dynamica lly changing database integrity is evaluation cost. This cost associated wi th performance of checking mechanisms is the main quantitative measure whic h must be supervised carefully. Based on literature, evaluating an integrit y constraint cost includes these main components: (i) data amount accessed; (ii) data amount transferred across network; and (iii) number of sites inv olved. In distributed databases, where many networked sites are involved, n ot only amount of data accessed must be minimized but also amount of data t ransferred across network and number of sites involved. In [Ibrahim H, Gray WA, Fiddian NJ. SICSDD: Techniques and implementation. In Proceedings of C onstraint Databases and Applications, Second International Workshop on Cons traint Database Systems (CDB'97), Delphi, Greece, January 1997, pp 187-207] , we introduced an integrity constraint subsystem for a relational distribu ted database. The subsystem consists of several techniques necessary for ef ficient constraint checking, particularly in a distributed environment wher e data distribution is transparent to application domain. Here, we show how these techniques effectively reduce constraint checking cost in such a dis tributed environment. This is done by analyzing and comparing generated sim plified forms to respective initial constraints respecting amount of data t o be accessed, amount of data transferred across network, and number of sit es involved during evaluation of constraints or simplified forms. Generally , our strategy reduces data amount needing to be accessed since only fragme nts of relations subject to update are evaluated. Data amount transferred a cross network and number of sites that are involved are minimized by evalua ting simplified forms at target site, i.e., site where update is performed. (C) 2001 John Wiley & Sons, Inc.