[LUCENE-3787] Improve Norms merging APIs

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 4.0-ALPHA
• Lucene Fields: New
• Assignee: Unassigned
• Reporter: Robert Muir
• Created: 14/Feb/12 18:25
• Updated: 28/Aug/22 13:08

Description

Spinoff from LUCENE-2632, since it took us a fair amount of time to track down,
I think its worth trying to improve the API.

The DocValuesConsumer api's default merge implementation calls canMerge/getDocValuesForMerge/getDocValuesType (protected methods).

but its a little strange how this works:

• all norms implementations must override the default DV implementation, or they might accidentally merge docvalues into their norms!
• preflex-RW only overrides 2 of these... how is its norms merging working... is it?
• its tricky obviously for issues like LUCENE-2632: as delegating merge() is not very obvious either.

So I think we should look at this, instead of having all NormsWriters override DocValues, redefining these methods in a way thats
not a "is-a" relationship, we could do something else like have split NormsConsumer/DVConsumer apis that share a package-private base class.

This way a norms impl just extends NormsConsumer and there are no traps.