Gilad Barkai created LUCENE-5316:
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Summary: Taxonomy tree traversing improvement
Key: LUCENE-5316
URL: https://issues.apache.org/jira/browse/LUCENE-5316
Project: Lucene - Core
Issue Type: Improvement
Components: modules/facet
Reporter: Gilad Barkai
Priority: Minor
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 internals.
A later issue(s?) could be opened to address the gaps once this one is done.
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