What is top-k retrieval? Result counts and evidence coverage
Understand returned counts, internal candidates, reranking cutoffs, filters, and approximate search through multi-passage questions.
Understand the concept
Top-k retrieval returns the highest-ranked k results, controlling count rather than accuracy. Internal candidate counts and reranking cutoffs can be separate settings. Small k can miss evidence; large k adds noise and context. Filters and approximate search affect actual returns, requiring interface- and task-specific checks.
Retrieval counts differ from generation sampling
Retrieval k counts documents or passages, while generation top-k filters token candidates. Returning five passages does not restrict generation to five tokens. Record each setting’s stage and field name.
Pinecone defines counts of returned similar records; Elastic distinguishes k from search-candidate settings. Check current versions and limits. This explains parameters without service calls or a universal k recommendation.
More results do not necessarily mean more independent evidence
Overlapping chunks can fill top positions with one passage, so larger k may still miss exceptions. Inspect distinct source evidence rather than count results. Questions needing a rule and exception expose this problem.
Short lists after filtering can result from candidate filtering rather than an empty permitted corpus. Approximate search breadth matters too. Inspect filter modes and candidates instead of only increasing final counts.
Balance evidence coverage against answer noise
Compare necessary passages for several k values on fixed queries and versions, then inspect distraction in generated answers. This is evaluation design without measured gains. Record token usage and latency to assess overhead.
No k can recover unindexed evidence. Poor ranking may require chunking or reranking changes. Choose from actual failures rather than assuming larger is safer. Source verification remains necessary regardless of result count.
Checked sources
These sources support the concepts and methods described here. Examples and test scope are labeled separately; check the version of the tools you use.