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https://issues.apache.org/jira/browse/LUCENE-2271?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12835758#action_12835758
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Robert Muir commented on LUCENE-2271:
-------------------------------------
bq. OK, so it was a design bug too.
A design bug that function queries score docs with an invalid score (NaN)
instead of throwing an exception?
> Function queries producing scores of -inf or NaN (e.g. 1/x) return incorrect
> results with TopScoreDocCollector
> --------------------------------------------------------------------------------------------------------------
>
> Key: LUCENE-2271
> URL: https://issues.apache.org/jira/browse/LUCENE-2271
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Search
> Affects Versions: 2.9
> Reporter: Uwe Schindler
> Priority: Minor
> Fix For: 2.9.2, 3.0.1, 3.1
>
> Attachments: LUCENE-2271.patch, LUCENE-2271.patch, TSDC.patch
>
>
> This is a foolowup to LUCENE-2270, where a part of this problem was fixed
> (boost = 0 leading to NaN scores, which is also un-intuitive), but in
> general, function queries in Solr can create these invalid scores easily. In
> previous version of Lucene these scores ordered correct (except NaN, which
> mixes up results), but never invalid document ids are returned (like
> Integer.MAX_VALUE).
> The problem is: TopScoreDocCollector pre-fills the HitQueue with sentinel
> ScoreDocs with a score of -inf and a doc id of Integer.MAX_VALUE. For the HQ
> to work, this sentinel must be smaller than all posible values, which is not
> the case:
> - -inf is equal and the document is not inserted into the HQ, as not
> competitive, but the HQ is not yet full, so the sentinel values keep in the
> HQ and result is the Integer.MAX_VALUE docs. This problem is solveable (and
> only affects the Ordered collector) by chaning the exit condition to:
> {code}
> if (score <= pqTop.score && pqTop.doc != Integer.MAX_VALUE) {
> // Since docs are returned in-order (i.e., increasing doc Id), a document
> // with equal score to pqTop.score cannot compete since HitQueue favors
> // documents with lower doc Ids. Therefore reject those docs too.
> return;
> }
> {code}
> - The NaN case can be fixed in the same way, but then has another problem:
> all comparisons with NaN result in false (none of these is true): x < NaN, x
> > NaN, NaN == NaN. This leads to the fact that HQ's lessThan always returns
> false, leading to unexspected ordering in the PQ and sometimes the sentinel
> values do not stay at the top of the queue. A later hit then overrides the
> top of the queue but leaves the incorrect sentinels unchanged -> invalid
> results. This can be fixed in two ways in HQ:
> Force all sentinels to the top:
> {code}
> protected final boolean lessThan(ScoreDoc hitA, ScoreDoc hitB) {
> if (hitA.doc == Integer.MAX_VALUE)
> return true;
> if (hitB.doc == Integer.MAX_VALUE)
> return false;
> if (hitA.score == hitB.score)
> return hitA.doc > hitB.doc;
> else
> return hitA.score < hitB.score;
> }
> {code}
> or alternatively have a defined order for NaN (Float.compare sorts them after
> +inf):
> {code}
> protected final boolean lessThan(ScoreDoc hitA, ScoreDoc hitB) {
> if (hitA.score == hitB.score)
> return hitA.doc > hitB.doc;
> else
> return Float.compare(hitA.score, hitB.score) < 0;
> }
> {code}
> The problem with both solutions is, that we have now more comparisons per hit
> and the use of sentinels is questionable. I would like to remove the
> sentinels and use the old pre 2.9 code for comparing and using PQ.add() when
> a competitive hit arrives. The order of NaN would be unspecified.
> To fix the order of NaN, it would be better to replace all score comparisons
> by Float.compare() [also in FieldComparator].
> I would like to delay 2.9.2 and 3.0.1 until this problem is discussed and
> solved.
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