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https://issues.apache.org/jira/browse/LUCENE-6179?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14275430#comment-14275430
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Adrien Grand commented on LUCENE-6179:
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> how does it work for BS1?
It uses a bit set for sorting. Since the scorer scores windows of 2048
documents (2^11, just like before), every document in a window can be given an
id between 0 and 2048 ({{docId & 2047}}), and this id is used as an index in
the bit set. When all sub-scorers have scored the window, we iterate over the
one bits in order and feed the collector.
This bit set only has 32 longs (2048 / 64), so iterating over it is rather fast
even if it's sparse. There also is a {{hasMatches}} boolean which is used to
quickly escape the loop in case no sub scorers matched.
> Remove out-of-order scoring
> ---------------------------
>
> Key: LUCENE-6179
> URL: https://issues.apache.org/jira/browse/LUCENE-6179
> Project: Lucene - Core
> Issue Type: Improvement
> Reporter: Adrien Grand
> Assignee: Adrien Grand
> Fix For: 5.0, Trunk
>
> Attachments: LUCENE-6179.patch, bool_or.tasks
>
>
> Out-of-order currently adds complexity that I would like to remove. Here is a
> selection of issues that come from out-of-order scoring.
> - lots of specializations with collectors: we have two versions of every top
> score/field collector depending on whether it should support out-of-order
> collection or not
> - it feels like it should be an implementation detail of our bulk scorers
> but it also makes our APIs more complicated, eg.
> LeafCollector.acceptsDocsOutOfOrder
> - if you create a TopFieldCollector, how do you know if you should pass
> docsScoredInOrder=true or false? To make the decision, you actually need to
> know whether your query supports out-of-order scoring while the API is on
> Weight.
> I initially wanted to keep it and improve the decision process in LUCENE-6172
> but I'm not sure it's the right approach as it would require to make the API
> even more complicated... hence the suggestion to remove out-of-order scoring
> completely.
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