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From "Gilad Barkai (JIRA)" <>
Subject [jira] [Updated] (LUCENE-5316) Taxonomy tree traversing improvement
Date Wed, 30 Oct 2013 14:21:36 GMT


Gilad Barkai updated LUCENE-5316:

    Attachment: LUCENE-5316.patch

{{TaxonomyReader.getParallelTaxonomyArrays}} is now protected, the implementation is only
on {{DirectoryTaxonomyReader}} in which it is protected as well.

Parallel arrays are only used in tests ATM - all tree traversing is done using {{TaxonomyReader.getChildre(int
ordinal)}} which is now abstract, and implemented in DirTaxoReader.

Mike, if you could please run this patch against the benchmarking maching it would be awesome
- as the direct array access is now switched with a method call (iterator's {{.next()}}

I hope we will not see any significant degradation.

> Taxonomy tree traversing improvement
> ------------------------------------
>                 Key: LUCENE-5316
>                 URL:
>             Project: Lucene - Core
>          Issue Type: Improvement
>          Components: modules/facet
>            Reporter: Gilad Barkai
>            Priority: Minor
>         Attachments: LUCENE-5316.patch
> The taxonomy traversing is done today utilizing the {{ParallelTaxonomyArrays}}. In particular,
two taxonomy-size {{int}} arrays which hold for each ordinal it's (array #1) youngest child
and (array #2) older sibling.
> This is a compact way of holding the tree information in memory, but it's not perfect:
> * Large (8 bytes per ordinal in memory)
> * Exposes internal implementation
> * Utilizing these arrays for tree traversing is not straight forward
> * Lose reference locality while traversing (the array is accessed in increasing only
entries, but they may be distant from one another)
> * In NRT, a reopen is always (not worst case) done at O(Taxonomy-size)
> This issue is about making the traversing more easy, the code more readable, and open
it for future improvements (i.e memory footprint and NRT cost) - without changing any of the
> A later issue(s?) could be opened to address the gaps once this one is done.

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