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From Benson Margulies <bimargul...@gmail.com>
Subject Re: Repeatability of results
Date Mon, 02 Apr 2012 21:41:46 GMT
On Mon, Apr 2, 2012 at 5:33 PM, Michael McCandless
<lucene@mikemccandless.com> wrote:
> Hmm that's odd.
>
> If the scores were identical I'd expect different sort order, since we
> tie-break by internal docID.
>
> But if the scores are different... the insertion order shouldn't
> matter.  And, the score should not change as a function of insertion
> order...

Well, I assumed that TF-IDF would wiggle.

>
> Do you have a small test case?

SInce this surprises you, I will build a test case.


>
> Mike McCandless
>
> http://blog.mikemccandless.com
>
> On Mon, Apr 2, 2012 at 5:28 PM, Benson Margulies <bimargulies@gmail.com> wrote:
>> We've observed something that, in some ways, is not surprising.
>>
>> If you take a set of documents that are close in 'score' to some query,
>>
>>  and shuffle them in different orders
>>
>>  and then see what results you get in what order from the reference query,
>>
>> the scores will vary according to the insertion order.
>>
>> I can't see any way to argue that it's wrong, but we find it
>> inconvenient when we are testing something and we want to multithread
>> the test to speed it up, thus making the insertion order
>> nondeterministic.
>>
>> It occurred to me that perhaps you all have some similar concerns in
>> testing lucene itself, and might have some advice about how to get
>> around it, thus this email.
>>
>> We currently observe this with 2.9.1 and 3.5.0.
>>
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>
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