Estimating the Output Cardinality of Partial Preaggregation with a Measure of Clusteredness Sven Helmer, Thomas Neumann, and Guido Moerkotte   View Paper (PDF)   Return to Aggregation, Prediction & Constraints (Session B8) Abstract We introduce a new parameter, the clus- teredness of data, and show how it can be used for estimating the output cardinal- ity of a partial preaggregation operator. This provides the query optimizer with an important piece of information for de- ciding whether the application of partial preaggregation is bene cial. Experimen- tal results are very promising, due to the high accuracy of the cardinality estima- tion based on our measure of clustered- ness. ©2004 Association for Computing Machinery