[LUCENE-7975] Replace facets taxonomy writer "cache" with BytesRefHash based implementation

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 7.1, 8.0
• Lucene Fields: New
• Assignee: Michael McCandless
• Reporter: Michael McCandless
• Created: 25/Sep/17 13:11
• Updated: 28/Aug/22 15:19
• Resolved: 03/Oct/17 14:04

Description

When the facets module was first created we didn't have BytesRefHash and so the default cache (Cl2oTaxonomyWriterCache was quite a bit more complex than needed.

I changed this to use a BytesRefHash, which stores labels as UTF8 (reduces memory for ascii-only usage), and is also faster (~12% overall speedup on indexing time in my private tests).