问题描述
如何搜索引擎从倒排索引合并的结果？
How do search engines merge results from an inverted index?
例如，如果我搜索的单词狗和蝙蝠，将有两个巨大的其中包含两个词之一的每一份文件的列表。在倒排索引
For example, if I searched for the inverted indexes of the words "dog" and "bat", there would be two huge lists of every document which contained one of the two words.
我怀疑搜索引擎走过这些名单，一个文档的时间，并试图找到名单的结果匹配。什么是做算法，使这一合并过程极快的？
I doubt that a search engine walks through these lists, one document at a time, and tries to find matches with the results of the lists. What is done algorithmically to make this merging process blazing fast?
推荐答案
其实搜索引擎的不的合并这些文件列表。他们获得良好的性能通过使用其它技术，其中最重要的是修剪：例如，对于每一个字的文档存储在顺序递减的PageRank的，并得到具有渐入头10的机会的结果（这将显示给用户），您可以遍历狗和蝙蝠名单只是一个相当小的部分，比如说，第一千。 （而且，当然，有高速缓存，但是这不涉及到非常查询执行算法）
Actually search engines do merge these document lists. They gain good performance by using other techniques, the most important of which is pruning: for example, for every word the documents are stored in order of decreasing pagerank, and to get results that have a chance of getting into the first 10 (which will be shown to the user) you may traverse just a fairly small portion of the dog and bat lists, say, the first thousand. (and, of course, there's caching, but that's not related to the very query execution algorithm)
此外，毕竟，没有的是的关于狗和蝙蝠左右许多文件：即使是数以百万计，它变成双秒以良好的实施
Besides, after all, there are not that many documents about dogs and about bats: even if it's millions, it turns into split seconds with a good implementation.
P.S。我曾在我国领先的搜索引擎，但是，不是在我们的旗舰搜索产品非常引擎，但我跟它的开发，惊讶地知道，查询执行的算法实际上是非常愚蠢的：事实证明，人们可以壁球一巨大的计算量到可以接受的时间范围。这完全是非常优化的，当然，但没有魔法，没有奇迹。
P.S. I worked at our country's leading search engine, however, not in the very engine of our flagship search product, but I talked to its developers and was surprised to know that query execution algorithms are actually fairly dumb: it turns out that one may squash a huge amount of computation into acceptable time bounds. It is all very optimized of course, but there's no magic and no miracles.
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