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https://issues.apache.org/jira/browse/LUCENE-8867?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16866785#comment-16866785
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Adrien Grand commented on LUCENE-8867:
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This is only an issue in the case that not all dimensions are indexed, right?
Otherwise you could figure out that all values are equal in
IntersectVisitor#compare?
One concern I have with the patch is that it assumes that the codec has doc IDs
available in an int[] slice as opposed to streaming them from disk directly to
the IntersectVisitor for instance.
> Optimise BKD tree for low cardinality leaves
> --------------------------------------------
>
> Key: LUCENE-8867
> URL: https://issues.apache.org/jira/browse/LUCENE-8867
> Project: Lucene - Core
> Issue Type: Improvement
> Reporter: Ignacio Vera
> Priority: Major
> Time Spent: 10m
> Remaining Estimate: 0h
>
> Currently if a leaf on the BKD tree contains only few values, then the leaf
> is treated the same way as it all values are different. It many cases it can
> be much more efficient to store the distinct values with the cardinality.
> In addition, in this cases the method IntersectVisitor#visit(docId, byte[])
> is called n times with the same byte array but different docID. This issue
> proposes to add a new method to the interface that accepts an array of docs
> so it can be override by implementors and gain search performance.
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