Self-tuning cost modeling of user-defined functions in an object-relational DBMS Byung Suk Lee, Robert R. Snapp, and Zhen He   View Paper (PDF)   Return to September 2005, Volume 30, Issue 3 Abstract ast;-tree. The other is a summary-based technique which uses the quadtree to store summary values at multiple resolutions. We have performed extensive performance evaluations comparing these two techniques against existing histogram-based techniques and the KNN technique, using both real and synthetic UDFs/data sets. The results show our techniques provide better performance in most situations considered. ©2006 Association for Computing Machinery