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https://issues.apache.org/jira/browse/LUCENE-4715?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13561672#comment-13561672
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Shai Erera commented on LUCENE-4715:
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bq. so you get the gains of NO_PARENTS without the cost (end rollup)
I'd like to clarify the difference between the 3 OrdinalPolicies, through
example. Say that you add the facet Date/2010/March/11, then the ordinals that
will be encoded are of:
* ALL_PARENTS: Date, Date/2010, Date/2010/March, Date/2010/March/11 (4 ordinals)
* NO_PARENTS: Date/2010/March/11 (1 ordinal)
* ALL_BUT_DIMENSION: Date/2010, Date/2010/March, Date/2010/March/11 (3 ordinals)
The aggregation of ALL_PARENTS and ALL_BUT_DIM is the same, but you don't get
the count of Date/ with the latter policy.
The aggregation of NO_PARENTS is the same as ALL_PARENTS, only you need to do
the rollup in the end.
Maybe we should have just ALL and ALL_BUT_DIM? Given the results of NO_PARENTS
(not that significant gains), and the complexity involved (i.e. currently only
CountingFC supports it) ...
But I just wanted to clarify the differences, because the ALL_BUT_DIM is not
that much different than ALL, except that you'll encode and decode the same
ordinal for many documents, so that has got to buy us something ...
> Add OrdinalPolicy.ALL_BUT_DIMENSION
> -----------------------------------
>
> Key: LUCENE-4715
> URL: https://issues.apache.org/jira/browse/LUCENE-4715
> Project: Lucene - Core
> Issue Type: Improvement
> Components: modules/facet
> Reporter: Shai Erera
> Assignee: Shai Erera
>
> With the move of OrdinalPolicy to CategoryListParams,
> NonTopLevelOrdinalPolicy was nuked. It might be good to restore it, as
> another enum value of OrdinalPolicy.
> It's the same like ALL_PARENTS, only doesn't add the dimension ordinal, which
> could save space as well as computation time. It's good for when you don't
> care about the count of Date/, but only about its children counts.
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