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From Nicolas Guyot <sfni...@gmail.com>
Subject Re: sorting with lucene 4.3
Date Wed, 31 Jul 2013 18:51:14 GMT
thanks Adrien for the explanation, it's really much appreciated.

I have written a quick test to reproduce the slower sorting with numeric
DV. In this test case, it happens only when reverse sorting.

About the sorting by page i mentioned, it was due to a mistake in our
testcase, sorry about that. I will make sure to test in a simpler
environment next time ;)




On Tue, Jul 30, 2013 at 3:13 PM, Adrien Grand <jpountz@gmail.com> wrote:

> Hi,
>
> On Tue, Jul 30, 2013 at 8:19 PM, Nicolas Guyot <sfnicow@gmail.com> wrote:
> > When sorting numerically, the search seems to take a bit of a while
> > compared to the lexically sorted search.
> > Also when sorting numerically the result is sorted within each page but
> no
> > globally as opposed to the lexical sorted search.
> >
> > From my understanding, a SortedDocValuesField is sorted while indexing
> but
> > not the NumericDocValuesField which is why we are facing those issues in
> > our implementation. Is that correct ?
>
> Sorted doc values are not exactly sorted, but Lucene computes all
> unique values, sorts them and assigns an ordinal to every unique
> value. These ordinals are then used at searching time to sort
> documents. When comparing documents on the same segment, Lucene
> directly uses the ordinals while when there are documents from
> different documents to compare, Lucene uses the values themselves
> (slower).
>
> I would expect sorting on a NumericDocValuesField to be faster since
> longs can be used to directly compare documents across all segments.
> Moreover, it is not normal that data is only sorted per page. Can you
> write a small piece of code that reproduces the problem?
>
> --
> Adrien
>
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