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https://issues.apache.org/jira/browse/LUCENE-4610?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13558686#comment-13558686
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Shai Erera commented on LUCENE-4610:
------------------------------------
LUCENE-4600 added CountingFacetsCollector which supports
OrdinalPolicy.NO_PARENTS (i.e. index only leaf nodes). Benchmark tests show
that it performs better than when all parents are indexed
(OrdinalPolicy.ALL_PARENTS), probably because less data is read from disk as
well as less computation done during search.
We might therefore make NO_PARENTS the default OrdinalPolicy, and therefore
need to address it for StandardFacetsAccumulator, perhaps in the form of a
NoParentsAccumulator.
> Implement a NoParentsAccumulator
> --------------------------------
>
> Key: LUCENE-4610
> URL: https://issues.apache.org/jira/browse/LUCENE-4610
> Project: Lucene - Core
> Issue Type: New Feature
> Components: modules/facet
> Reporter: Shai Erera
> Attachments: LUCENE-4610.patch
>
>
> Mike experimented with encoding just the exact categories ordinals on
> LUCENE-4602, and I added OrdinalPolicy.NO_PARENTS, with a comment saying that
> this requires a special FacetsAccumulator.
> The idea is to write the exact categories only for each document, and then at
> search time count up the parents chain to compute requested facets (I say
> count, but it can be any weight).
> One limitation of such accumulator is that it cannot be used when e.g. a
> document is associated with two categories who share the same parent, because
> that may result in incorrect weights computed (e.g. a document might have
> several Authors, and so counting the Author facet may yield wrong counts). So
> it can be used only when the app knows it doesn't add such facets, or that it
> always asks to aggregate a 'root' that in its path this criteria doesn't hold
> (no categories share the same parent).
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