[LUCENE-6553] Simplify how we handle deleted docs in read APIs

• Type: Improvement
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 5.3
• Lucene Fields: New
• Assignee: Adrien Grand
• Reporter: Adrien Grand
• Created: 11/Jun/15 21:10
• Updated: 15/Sep/24 22:23
• Resolved: 25/Jun/15 17:22

Description

Today, all scorers and postings formats need to be able to handle deleted documents.

I suspect that the reason is that we want to be able to make sure to not perform costly operations on documents that are deleted. For instance if you run a phrase query, reading positions on a document which is deleted is useless. I suspect this is also a source of inefficiencies since in some cases we apply deleted documents several times: for instance conjunctions apply deleted docs to every sub scorer.

However, with the new two-phase iteration API, we have a way to make sure that we never run expensive operations on deleted documents: we could first iterate over the approximation, then check that the document is not deleted, and finally confirm the match. Since approximations are cheap, applying deleted docs after them would not be an issue.

I would like to explore removing the "Bits acceptDocs" parameter from TermsEnum.postings, Weight.scorer, SpanWeight.getSpans and Weight.BulkScorer, and add it to BulkScorer.score. This way, bulk scorers would be the only API which would need to know how to apply deleted docs, which I think would be more manageable since we only have 3 or 4 impls. And DefaultBulkScorer would be implemented the way described above: first advance the approximation, then check deleted docs, then confirm the match, then collect. Of course that's only in the case the scorer supports approximations, if it does not, it means it is cheap so we can directly iterate the scorer and check deleted docs on top.