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From Ting Yao <ting.echo....@gmail.com>
Subject Re: How can Docvalues so efficient
Date Mon, 30 May 2016 10:52:48 GMT
Thank you very much for answering me.
 But could you explain how Lucene reads the doc values files sequentially?

2016-05-30 18:15 GMT+08:00 Adrien Grand <jpountz@gmail.com>:

> 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.yao@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
> >
>



-- 
Echo Yao

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