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https://issues.apache.org/jira/browse/LUCENE-2271?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12836183#action_12836183
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Robert Muir commented on LUCENE-2271:
-------------------------------------
bq. In my opinion we should fix it using the attached patch and in the future
3.1 do some refactoring:
in general agree, on one condition that it doesnt slow down normal queries,
MultiSearcher, or ParallelMultiSearcher significantly (benchmarks)
in my opinion the thing is documented not to work for these values, so its not
a bug at all. if we want to support these values we should redesign the
collector (in 3.1)
> 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, 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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