well, it is "approximate" KNN and can get caught in local minima
(maxima?). Increasing K has, indirectly, the effect of expanding the
search space because the minimum score in the priority score (score of
the Kth item) is used as a threshold for deciding when to terminate
the search
On Wed, Aug 2, 2023 at 5:19 PM Michael Wechner
<michael.wech...@wyona.com> wrote:
>
> Hi
>
> I use Lucene 9.7.0 but experienced the same behaviour with Lucene 9.6.0
> when doing vector search as follows:
>
> I have indexed about 200 vectors (dimension 768)
>
> I build the query as follows
>
> Query query = new KnnFloatVectorQuery("vector-field-name",
> queryVector, k);
>
> and do the search as follows:
>
> TopDocs topDocs = searcher.search(query, k);
>
> When I set k=27 then the top doc has a score of 0.7757
>
> When I set the "k" value a little lower, e.g. k=24 then the top doc has
> a score of 0.7319 and is not the same document as the one with the score
> of 0.7757
>
> And idea what I might be doing wrong or what I misunderstand?
>
> Why does the value of k has an effect on the returned top doc?
>
> Thanks
>
> Michael
>
>
>
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