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From "Uwe Schindler" <...@thetaphi.de>
Subject RE: Merging results from two searches on two separate Searchers
Date Wed, 15 Feb 2012 00:46:00 GMT
Scores are only compatible if the query is the same, which is not the case for you. So you
cannot merge hits from different queries.

-----
Uwe Schindler
H.-H.-Meier-Allee 63, D-28213 Bremen
http://www.thetaphi.de
eMail: uwe@thetaphi.de


> -----Original Message-----
> From: Trejkaz [mailto:trejkaz@trypticon.org]
> Sent: Wednesday, February 15, 2012 1:40 AM
> To: Lucene Users Mailing List
> Subject: Merging results from two searches on two separate Searchers
> 
> Hi all.
> 
> We have 1..N indexes for each time someone adds some data. Each time they
> can choose different tokenisation settings. Because of this, each text index has
> its own query parser instance. Because each query parser could generate a
> different Query (though I guess whether they do or not is another matter!) we
> can't just use MultiReader and a single IndexSearcher.
> 
> What we have been doing is performing the search against each index and then
> merging the results by score. I remember from a long time ago that this was
> not something you're supposed to do.
> 
> Reading information I can find today, it sounds like the main problem was Hits
> doing score normalisation. We cloned Hits a while back and inherited its score
> normalisation code as well.
> 
> So my questions:
>   - does normalising the scores do anything other than give people the illusion
> that scores are from 0.0 ~ 1.0?
>   - if I remove the score normalisation from our Hits-like class, is it now totally
> OK to merge the lists of results?
>     (And, I guess, if not, is there some trick I can employ to line the scores for the
> results up so that I can?)
> 
> TX
> 
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