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https://issues.apache.org/jira/browse/SOLR-8559?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Dennis Gove reopened SOLR-8559:
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> 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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