[SOLR-9125] CollapseQParserPlugin allocations are index based, not query based

• Type: Improvement
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Component/s: query parsers
• Labels: collapsingQParserPlugin
• Assignee: Unassigned
• Reporter: Jeff Wartes
• Created: 17/May/16 16:04
• Updated: 05/Apr/20 11:49

Description

Among other things, CollapsingQParserPlugin’s OrdScoreCollector allocates space per-query for:
1 int (doc id) per ordinal
1 float (score) per ordinal
1 bit (FixedBitSet) per document in the index

So the higher the cardinality of the thing you’re grouping on, and the more documents in the index, the more memory gets consumed per query. Since high cardinality and large indexes are the use-cases CollapseQParserPlugin was designed for, I thought I'd point this out.

My real issue is that this does not vary based on the number of results in the query, either before or after collapsing, so a query that results in one doc consumes the same amount of memory as one that returns all of them. All of the Collectors suffer from this to some degree, but I think OrdScore is the worst offender.

Issue Links

• is related to: SOLR-14365 CollapsingQParser - Avoiding always allocate int[] and float[] with size equals to number of unique values