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https://issues.apache.org/jira/browse/LUCENE-7628?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15823736#comment-15823736
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Adrien Grand commented on LUCENE-7628:
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I think that would work, but Collector is another API where I'd like to be
careful about adding new methods. I think {{needsScores}} was very compelling
because it enabled significant optimizations as well as merging queries and
filters. I think I would need more compelling use-cases to be convinced about
adding such a new API on Collector. Out of curiosity, would it work for your
use-case if the introspection API was on Weight rather than Scorer? That would
work better for me since Weight is not exposed in Collector like Scorer and
does not have the same performance requirements.
> Add a getMatchingChildren() method to DisjunctionScorer
> -------------------------------------------------------
>
> Key: LUCENE-7628
> URL: https://issues.apache.org/jira/browse/LUCENE-7628
> Project: Lucene - Core
> Issue Type: Improvement
> Reporter: Alan Woodward
> Assignee: Alan Woodward
> Priority: Minor
> Fix For: 6.4
>
> Attachments: LUCENE-7628.patch
>
>
> This one is a bit convoluted, so bear with me...
> The luwak highlighter works by rewriting queries into their Span-equivalents,
> and then running them with a special Collector. At each matching doc, the
> highlighter gathers all the Spans objects positioned on the current doc and
> collects their positions using the SpanCollection API.
> Some queries can't be translated into Spans. For those queries that generate
> Scorers with ChildScorers, like BooleanQuery, we can call .getChildren() on
> the Scorer and see if any of them are SpanScorers, and for those that aren't
> we can call .getChildren() again and recurse down. For each child scorer, we
> check that it's positioned on the current document, so non-matching
> subscorers can be skipped.
> This all works correctly *except* in the case of a DisjunctionScorer where
> one of the children is a two-phase iterator that has matched its
> approximation, but not its refinement query. A SpanScorer in this situation
> will be correctly positioned on the current document, but its Spans will be
> in an undefined state, meaning the highlighter will either collect incorrect
> hits, or it will throw an Exception and prevent hits being collected from
> other subspans.
> We've tried various ways around this (including forking SpanNearQuery and
> adding a bunch of slow position checks to it that are used only by the
> highlighting code), but it turns out that the simplest fix is to add a new
> method to DisjunctionScorer that only returns the currently matching child
> Scorers. It's a bit of a hack, and it won't be used anywhere else, but it's
> a fairly small and contained hack.
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