[SOLR-15047] 'collapse' on numeric field treats all docs with '0' in collapse field as part of the null group

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 8.8, 9.0
• Assignee: Chris M. Hostetter
• Reporter: Chris M. Hostetter
• Created: 14/Dec/20 22:09
• Updated: 12/May/22 00:26
• Resolved: 06/Jan/21 18:04

Description

The CollapseQParser has some very, very, old code/semantics in it that date back to when the FieldCache was incapable of differentiating between a document that contained '0' in the field being un-inverted, and a document that didn't have any value in that field.

This limitation does not exist in DocValues (nor has it existed for a long time) but as the DocValues API has evolved, and as the collapse code has been updated to take advantage of the newer APIs that make it obvious when a document has no value in a field, the collapse code still explicitly equates "0" in a numeric field with the "null group"

We can/should fix this bug so that the behavior is sane.

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Known workaround for this problem: (redundantly) index a "string" version of the field being collapsed on - but this is a poor substitute fro being able to efficiently collapse on numeric fields (which take up less space on disk and in the collapse data structures)

Issue Links

• is blocked by: SOLR-15048 collapse + query elevation behaves inconsistenty w/ 'null group' docs depending on group head selector
• is related to: SOLR-15078 ExpandComponent treats all docs with '0' in a numeric collapse field the same as if null