[LUCENE-8050] PerFieldDocValuesFormat's merge should not grab field DVF if DocValuesType.NONE

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 6.3
• Fix Version/s: 8.6
• Component/s: core/index
• Lucene Fields: New
• Assignee: David Smiley
• Reporter: David Smiley
• Created: 16/Nov/17 18:39
• Updated: 28/Aug/22 15:21
• Resolved: 07/Apr/20 20:29

Description

Since LUCENE-7456 (Lucene 6.3), PerFieldDocValuesFormat delegates the merge to the actual field DVF's merge. Great, but unfortunately it will call getDocValuesFormatForField on all fields (in FieldInfos) even those that have no DocValues (DocValuesType.NONE). It won't ultimately actually write anything to those DVFs but there may be some overhead and furthermore it's now more awkward to write a subclass of PFDVF that deliberately throws an exception from getDocValuesFormatForField for some fields.

AFAICT this appears to be a non-issue for PerFieldPostingsFormat's merge because it's use of MultiFields filters out IndexOptions.NONE

Issue Links

• is related to: LUCENE-7456 PerField(DocValues|Postings)Format do not call the per-field merge methods
• links to: GitHub Pull Request #1408