While Knuth has justly warned that "premature optimization is the root of all evil," the whole point of an index is to find information fast, so this column addresses performance issues as well.
尽管Knuth曾经忠告我们：“不成熟的优化是问题的根源”，但索引的目的在于快速地找到信息，因此本专栏同时也将讨论性能问题。
If no index is found, then there are no cached tweets, so there is nothing to show and no optimization can be made on the query (and you return a value of 0 to indicate this).
如果没找到任何索引，那么就没有缓存的tweet，所以就没有展示的东西，并且没有可对查询进行的优化(您返回一个0值以指示这一点)。
Optimization results in the merging of many of the Lucene index files into a single file.
优化会导致多个Lucene索引文件合并成一个单一文件。
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