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https://issues.apache.org/jira/browse/LUCENE-6553?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14582568#comment-14582568
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Robert Muir commented on LUCENE-6553:
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I agree this is definitely worth exploring, it could simplify a lot.
{quote}
I suspect this is also a source of inefficiencies since in some cases we apply
deleted documents several times: for instance conjunctions apply deleted docs
to every sub scorer.
{quote}
It also has the side effect of making code complex: trying to avoid these
inefficiencies in other cases, such as in advance(). So code is completely
duplicated from next() there just to avoid the livedocs check on every document
when scanning.
> Simplify how we handle deleted docs in read APIs
> ------------------------------------------------
>
> Key: LUCENE-6553
> URL: https://issues.apache.org/jira/browse/LUCENE-6553
> Project: Lucene - Core
> Issue Type: Improvement
> Reporter: Adrien Grand
> Assignee: Adrien Grand
> Priority: Minor
> Fix For: Trunk
>
>
> Today, all scorers and postings formats need to be able to handle deleted
> documents.
> I suspect that the reason is that we want to be able to make sure to not
> perform costly operations on documents that are deleted. For instance if you
> run a phrase query, reading positions on a document which is deleted is
> useless. I suspect this is also a source of inefficiencies since in some
> cases we apply deleted documents several times: for instance conjunctions
> apply deleted docs to every sub scorer.
> However, with the new two-phase iteration API, we have a way to make sure
> that we never run expensive operations on deleted documents: we could first
> iterate over the approximation, then check that the document is not deleted,
> and finally confirm the match. Since approximations are cheap, applying
> deleted docs after them would not be an issue.
> I would like to explore removing the "Bits acceptDocs" parameter from
> TermsEnum.postings, Weight.scorer, SpanWeight.getSpans and Weight.BulkScorer,
> and add it to BulkScorer.score. This way, bulk scorers would be the only API
> which would need to know how to apply deleted docs, which I think would be
> more manageable since we only have 3 or 4 impls. And DefaultBulkScorer would
> be implemented the way described above: first advance the approximation, then
> check deleted docs, then confirm the match, then collect. Of course that's
> only in the case the scorer supports approximations, if it does not, it means
> it is cheap so we can directly iterate the scorer and check deleted docs on
> top.
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