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https://issues.apache.org/jira/browse/LUCENE-4610?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13529716#comment-13529716
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Gilad Barkai commented on LUCENE-4610:
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Since taxonomies do not tend to change in depth (i.e, if FileType has only
depth 1, it is not likely it will suddenly grow to depth 3) - than perhaps the
definition of "these N dimensions are single-valued" should be set in a
CategoryListParam ?
Shai mentioned yesterday that adding the parents during aggregation is
problematic when partitions are in place. Parents might not be on the same
partition as their children, nor the aggregator is aware of the partition it is
currently aggregating upon. For partitions it seems adding the parents in a
post process - as was first suggested - is the right approach.
> 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
>
> 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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