A spinoff from
LUCENE-3146. Consider the following two scenarios, according to how 4.0 currently works:
- Field "a" is added w/ norms. Sometime later field "a" is added to a document w/o norms – norms are disabled for field "a", for all docs.
- Field "a" is added w/o norms - norms are disabled for field "a". Sometime later field "a" is added to a document w/ norms – app thinks norms were added, while in fact they are dropped.
This is a bug and case #2 should fail on add/updateDocument - app should know norms were not added. While case #1 isn't great either, it's the only way an app can choose to disable norms for field "a", after instances of it already contain norms, so we should support that scenario.
In order to detect that early, we should track norms info in .fnx, as Mike describes at
LUCENE-3146. Since this changes the index format, we should also update the "file format" page after we do it.
Not sure what's the deal w/ 3.x indexes that are read by 4.0 code. Initially they won't have .fnx file, so no central norms information exist to detect the cases I've described above. Over time, as segments are merged, .fnx will include information from more and more segments, but there's always a chance few segments will still contain the norms for field "a". I'm not very familiar w/ that part of the code, but I think that:
- If .fnx says "no norms for field a", the we ignore any norms information that may or may not exist in segments.
- If .fnx says "norms for field a", then we need to make up some norms values for (old) segments w/ no norms? We need to make up values during segment merge and search?