Doc values indeed need to read from disk. However, the fact that Lucene reads the doc values files sequentially (disks perform better at sequential access than random access) and that the filesystem cache helps keep hot regions of the doc values files in memory usually helps keep perfermance close to what we would get if the data was stored in memory.
Le lun. 30 mai 2016 à 12:01, Ting Yao <ting.echo....@gmail.com> a écrit : > Hi all, > I am reading Lucene source code recently and we also use the Elastic > Search as our search engine. As far as I know, the elastic search > performance is pretty good. The elastic search is based on Lucene. So I am > wondering that how it can search words so fast when the field data > (uninverted index) are stored in disk. > The DocValues make access filed values fast. From my perspective， it's > of course fast when few values of a field are read. But when few fields > need to access, I think it's not fast again. Because when access a field, > all of its doc values need to read with MMap. So the system needs to read > disk to load the data. > So could anyone help me understand the DocValues operating mechanism? > > Echo Yao >
