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In this paper, the authors design and evaluate alternative selection placement strategies for optimizing a very large number of continuous queries in an Internet environment. Two grouping strategies, PushDown and PullUp, in which selections are either pushed below, or pulled above, joins are proposed and investigated. While the earlier research has demonstrated that the incremental group optimization can significantly outperform an ungrouped approach, the results from this paper show that different incremental group optimization strategies can have significantly different performance characteristics. Surprisingly, in the studies, PullUp, in which selections are pulled above joins, is often better and achieves an average 10-fold performance improvement over PushDown (Occasionally 100 times faster).
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