[LUCENE-5316] Taxonomy tree traversing improvement

• Type: Improvement
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Component/s: modules/facet
• Lucene Fields: New
• Assignee: Unassigned
• Reporter: Gilad Barkai
• Created: 30/Oct/13 09:15
• Updated: 28/Aug/22 13:56

Description

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.