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Sorting improves word-aligned bitmap indexes (2009)
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BibTeX
@MISC{Lemire09sortingimproves,
author = {Daniel Lemire and Owen Kaser and Kamel Aouiche},
title = {Sorting improves word-aligned bitmap indexes},
year = {2009}
}
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Abstract
Bitmap indexes must be compressed to reduce input/output costs and minimize CPU usage. To accelerate logical operations (AND, OR, XOR) over bitmaps, we use techniques based on run-length encoding (RLE), such as Word-Aligned Hybrid (WAH) compression. These techniques are sensitive to the order of the rows: a simple lexicographical sort can divide the index size by 9 and make indexes several times faster. We investigate row-reordering heuristics. Simply permuting the columns of the table can increase the sorting efficiency by 40%. Secondary contributions include efficient algorithms to construct and aggregate bitmaps. The effect of word length is also reviewed by constructing 16-bit, 32-bit and 64-bit indexes. Using 64-bit CPUs, we find that 64-bit indexes are slightly faster than 32-bit indexes despite being nearly twice as large.
Keyphrases
improves word-aligned bitmap index 64-bit index run-length encoding bitmap index secondary contribution word-aligned hybrid row-reordering heuristic logical operation simple lexicographical sort key word index several time index size efficient algorithm cpu usage word length 64-bit cpu input output cost
