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https://issues.apache.org/jira/browse/SOLR-8559?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15113133#comment-15113133
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David Smiley commented on SOLR-8559:
------------------------------------

[~dpgove] Please update the "Fix Version/s:" when resolving issues to the 
particular non-trunk release this is fixed on.  5.5?  It's multi-valued; and 
including trunk is generally implied, I usually omit that.  Also, I forget 
where I saw this but I think we're always supposed to mark issues as "Resolved" 
(not Closed) and then at the next release it gets bulk-updated to Closed by the 
RM.

And thanks for getting this in :-)

> FCS facet performance optimization
> ----------------------------------
>
>                 Key: SOLR-8559
>                 URL: https://issues.apache.org/jira/browse/SOLR-8559
>             Project: Solr
>          Issue Type: Improvement
>          Components: faceting
>    Affects Versions: 5.4, Trunk
>            Reporter: Keith Laban
>            Assignee: Dennis Gove
>              Labels: optimization, performance
>             Fix For: Trunk
>
>         Attachments: SOLR-8559-4-10-4.patch, SOLR-8559.patch, solr-8559.patch
>
>
> While profiling a large collection (multi-sharded billions of documents), I 
> found that a fast (5-10ms query) which had no matches would take 20-30 
> seconds when doing facets even when {{facet.mincount=1}}
> Profiling made it apparent that with {{facet.method=fcs}} 99% of the time was 
> [spent 
> here|https://github.com/apache/lucene-solr/blob/trunk/solr/core/src/java/org/apache/solr/request/PerSegmentSingleValuedFaceting.java#L212].
> {{queue.udpateTop}} gets called {{numOfSegments*numTerms}}, the worst case 
> when every term is in every segment. This formula doesn't take into account 
> whether or not any of the terms have a positive count with respect to the 
> docset.
> These optimizations are aimed to do two things:
> # When mincount>0 don't include segments which all terms have zero counts. 
> This should significantly speed up processing when terms are high cardinality 
> and the matching docset is small
> # FIXED TODO optimization: when mincount>0 move segment position the next non 
> zero term value.
> both of these changes will minimize the number of called needed to the slow 
> {{updateTop}} call.



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