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From Greg Bowyer <gbow...@fastmail.co.uk>
Subject Re: Merging results from two searches on two separate Searchers
Date Wed, 15 Feb 2012 00:53:47 GMT
Out of sheer curiosity what makes scores different across queries, I am 
not suggesting they should be the same, just filling in terrible gaps in 
my knowledge that I have not quite fathomed yet during source diving


On 14/02/12 16:46, Uwe Schindler wrote:
> 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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