为较小的索引重新排序列
Reordering Columns for Smaller Indexes
摘要：
面向列的索引（如投影或位图索引）通过行程长度编码进行压缩，以减少存储量并提高速度。对表进行排序可以提高压缩率。在实际的数据集上，在排序之前以正确的顺序排列列可以将运行次数减少两倍或更多。不幸的是，确定最佳列顺序是NP难的。对于许多情况下，我们证明了运行表列的数量是最小化，如果我们排序列增加基数。实验上，基于希尔伯特空间填充曲线的排序在最小化运行次数方面很差。
英文摘要：
Column-oriented indexes-such as projection or bitmap indexes-are compressed by run-length encoding to reduce storage and increase speed. Sorting the tables improves compression. On realistic data sets, permuting the columns in the right order before sorting can reduce the number of runs by a factor of two or more. Unfortunately, determining the best column order is NP-hard. For many cases, we prove that the number of runs in table columns is minimized if we sort columns by increasing cardinality. Experimentally, sorting based on Hilbert space-filling curves is poor at minimizing the number of runs.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
