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Journal Article

Non-uniformity Issues and Workarounds in Bounded-size Sampling


Gemulla,  Rainer
Databases and Information Systems, MPI for Informatics, Max Planck Society;

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Gemulla, R., Haas, P. J., & Lehner, W. (2013). Non-uniformity Issues and Workarounds in Bounded-size Sampling. The VLDB Journal, 22(6), 753-772. doi:10.1007/s00778-013-0307-0.

Cite as: https://hdl.handle.net/11858/00-001M-0000-0015-1A4D-1
A variety of schemes have been proposed in the literature to speed up query processing and analytics by incrementally maintaining a bounded-size uniform sample from a dataset in the presence of a sequence of insertion, deletion, and update transactions. These algorithms vary according to whether the dataset is an ordinary set or a multiset and whether the transaction sequence consists only of insertions or can include deletions and updates. We report on subtle non-uniformity issues that we found in a number of these prior bounded-size sampling schemes, including some of our own. We provide workarounds that can avoid the non-uniformity problem; these workarounds are easy to implement and incur negligible additional cost. We also consider the impact of non-uniformity in practice and describe simple statistical tests that can help detect non-uniformity in new algorithms.