[LUCENE-10206] Implement O(1) count on query cache

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 9.0
• Lucene Fields: New
• Assignee: Unassigned
• Reporter: Nik Everett
• Created: 26/Oct/21 14:32
• Updated: 28/Aug/22 16:29
• Resolved: 27/Oct/21 09:33

Description

I'd like to implement the `Weight#count` method in `LRUQueryCache` so cached queries can quickly return their counts. We already have a count on all of the bit sets we use for the query cache we just have to store it and "plug it in".

 

I got here because we frequently end up wanting to get counts and I saw hot `RoaringDocIdSet`'s iterator hot spotting. I don't think it's slow or anything, but when the collector is just `count++` the iterator is substantial. It seems like we could frequently avoid the whole thing by implementing `count` in the query cache.

Issue Links

• links to: GitHub Pull Request #415