[Xapian-discuss] Incorrect get_matches_estimated() of Xapian::Mset

[Hightman(马明练)]

Olly Betts,您好！

	Thanks for your help, Now I have resolved this problem at some degree.

======= 2007-09-20 15:36:00 您在来信中写道：=======

>On Thu, Sep 20, 2007 at 10:18:07PM +0800, Hightman(??????) wrote:
>>   Though I used the third argument to set the check_at_least number, It still return
>>   much more number than the exact number(about 5 times);
>> 
>>   But if the exact number is greater than estimated number, the new return value is more correct.
>> 
>>   Dosen't the third argument fixed the number greater than exact number?
>
>I don't really understand that question.
>
>What the checkatleast parameter specifies is the minimum number of
>documents which the matcher will look at.  By default we try to
>minimise this number, while still returning correct results, as
>that makes searches faster.
>
>If there are fewer matches than this, then get_matches_estimated(),
>get_matches_lower_bound() and get_matches_upper_bound() will all
>return the same answer, which will be the exact number of matches.
>
>So if you want to show 10 page buttons and have 10 hits per page,
>pass 101 as checkatleast (the extra 1 allows you to tell the
>difference between "exactly 100 hits" and "more than 100 hits").
>
>If there are more, then get_matches_estimated() won't necessarily
>be exact, though because the matcher may have looked at more documents,
>it may be a better estimate.  You can look at get_matches_lower_bound()
>and get_matches_upper_bound() to see how wrong it could be.
>
>Note that most search engines estimate the number of matches for
>reasons of performance (e.g. Google usually says "Results 1 - 10 of
>about 781,000").
>
>Cheers,
>    Olly

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　　　　　　　　Hightman(马明练)
　　　　　　　　hightman at zuaa.zju.edu.cn
　　　　　　　　　　2007-09-20