Overcoming Limitations of Sampling for Aggregation Queries

We study the problem of approximately answering aggregation queries using sampling. We observe that uniform sampling performs poorly when the distribution of the aggregated

attribute is skewed. To address this issue, we introduce a technique called outlier-indexing. Uniform sampling is also ineffective for queries with low selectivity. We rely on weighted sampling based on workload information to overcome this shortcoming. We demonstrate that a combination of outlier-indexing with weighted sampling can be used to answer aggregation queries with significantly reduced approximation error compared to either uniform sampling or weighted sampling alone. We discuss the implementation of these techniques on Microsoft’s SQL Server, and present experimental results that demonstrate the merits of our techniques.

PDF file

In  17th International Conference on Data Engineering

Publisher  IEEE Computer Society
Copyright © 2007 IEEE. Reprinted from IEEE Computer Society. This material is posted here with permission of the IEEE. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by writing to pubs-permissions@ieee.org. By choosing to view this document, you agree to all provisions of the copyright laws protecting it.


> Publications > Overcoming Limitations of Sampling for Aggregation Queries