[LUCENE-7617] Improve GroupingSearch API and extensibility

• Type: Improvement
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 6.4
• Lucene Fields: New
• Assignee: Alan Woodward
• Reporter: Alan Woodward
• Created: 03/Jan/17 11:33
• Updated: 28/Aug/22 15:08
• Resolved: 07/Jan/17 12:08

Description

While looking at how to make grouping work with the new XValuesSource API in core, I thought I'd try and clean up GroupingSearch a bit. We have three different ways of grouping at the moment: by doc block, using a single-pass collector; by field; and by ValueSource. The latter two both use essentially the same two-pass mechanism, with different Collector implementations.

I can see a number of possible improvements here:

• abstract the two-pass collector creation into a factory API, which should allow us to add the XValuesSource implementations as well
• clean up the generics on the two-pass collectors - maybe look into removing them entirely? I'm not sure they add anything really, and we don't have them on the equivalent plan search APIs
• think about moving the document block method into the join module instead, alongside all the other block-indexing code
• rename the various Collector base classes so that they don't have 'Abstract' in them anymore