What's the point of Lucene NumericUtils.IntToPrefixCoded

问题

I've been looking at Subtext's Lucene.Net implementation as a guide to do something similar with our websites. When Subtext index or search for a given post, it runs the ID through NumericUtils.IntToPrefixCoded. According to the Lucene docs, it does some shifting, but doesn't lose precision. So, what's the point? What does it do, and why?

回答1:

You need to look at the class documentation, which explains it in more detail:

To quickly execute range queries in Apache Lucene, a range is divided recursively into multiple intervals for searching: The center of the range is searched only with the lowest possible precision in the trie, while the boundaries are matched more exactly. This reduces the number of terms dramatically.

This class generates terms to achieve this: First the numerical integer values need to be converted to strings. For that integer values (32 bit or 64 bit) are made unsigned and the bits are converted to ASCII chars with each 7 bit. The resulting string is sortable like the original integer value. Each value is also prefixed (in the first char) by the shift value (number of bits removed) used during encoding.

As I understand, intToPrefixCoded method does exactly that: takes int value, shifts it and returns a sortable String as explained above.

来源：https://stackoverflow.com/questions/13414149/whats-the-point-of-lucene-numericutils-inttoprefixcoded