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From "Michael McCandless (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-7994) Use int/int hash map for int taxonomy facet counts
Date Mon, 23 Oct 2017 18:31:00 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-7994?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16215610#comment-16215610
] 

Michael McCandless commented on LUCENE-7994:
--------------------------------------------

bq. Those hash collisions, on the other hand, were possible to hit with trivial map-iteration-copying
blocks and they were nasty (and people rightfully didn't and couldn't anticipate them to happen).
So I went for "better slower than sorry" direction...

I agree that is the right tradeoff!  Reduce the chances of adversarial cases ...

Thanks [~dweiss].

> Use int/int hash map for int taxonomy facet counts
> --------------------------------------------------
>
>                 Key: LUCENE-7994
>                 URL: https://issues.apache.org/jira/browse/LUCENE-7994
>             Project: Lucene - Core
>          Issue Type: Improvement
>            Reporter: Michael McCandless
>            Assignee: Michael McCandless
>             Fix For: master (8.0), 7.2
>
>         Attachments: LUCENE-7994.patch, LUCENE-7994.patch
>
>
> Int taxonomy facets today always count into a dense {{int[]}}, which is wasteful in cases
where the number of unique facet labels is high and the size of the current result set is
small.
> I factored the native hash map from LUCENE-7927 and use a simple heuristic (customizable
by the user by subclassing) to decide up front whether to count sparse or dense.  I also made
loading of the large children and siblings {{int[]}} lazy, so that they are only instantiated
if you really need them.



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