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https://issues.apache.org/jira/browse/LUCENE-7254?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15257839#comment-15257839
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Adrien Grand commented on LUCENE-7254:
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bq. The sparse case is not the case to optimize because it is already fast.
I agree in general, but for instance right now points are an appealing way to
index unique ids (potentially with the version as a second dimension). With
this patch we would make lookups by id use O(maxDoc) memory and run in
O(maxDoc). Even though the constant factors of FixedBitSet are very low, this
is quite disappointing for an inverted structure.
> DocIDSetBuilder is no good for points
> -------------------------------------
>
> Key: LUCENE-7254
> URL: https://issues.apache.org/jira/browse/LUCENE-7254
> Project: Lucene - Core
> Issue Type: Bug
> Reporter: Robert Muir
> Attachments: LUCENE-7254.patch, LUCENE-7254.patch
>
>
> For the postings lists, I think this approach works well in dense cases (e.g.
> whole DISI's are added, things are coming in order, etc).
> However in the points case, it holds back range performance significantly.
> There are a couple of problems here:
> * expensive cardinality computation (this is a 2% hit) when its totally
> unnecessary. we can use index statistics to help here.
> * lots of conditional stuff in add(). This includes growing checks / bitset
> switching checks and so on (which happens even if you are smart and call
> grow, but this stuff all adds up).
> I dont think we should try to create a magical shared API that is both
> efficient for postings lists of unstructured stuff and at the same time point
> collection for structured fields, instead we should just do things
> differently for points and iterate from there.
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