Reranking
Quick Take
- In brief: A reranker reorders candidates after an initial search.
- Useful for: Putting the most relevant passages near the top.
- Main limit: It cannot rank a document that the first stage did not retrieve.
Overview
A search for “Why did OCR return nothing after upload?” may find pages about uploading, image processing, and OCR. A reranker can move the page that describes the exact flow to the top.
Core Definition
Reranking applies a more detailed relevance judgment to an initial set of retrieved candidates and changes their order.
Background and Evolution
Retrieval systems often use a fast first stage to find candidates, then a more detailed model to score a smaller set. This two-stage approach balances coverage and compute cost.
How It Works
The first retriever returns candidates. A reranker evaluates the query and each candidate together, assigns relevance scores, and sorts the list.
Applications in Software Development and Testing
Rerank code snippets or documentation pages before sending them to a coding assistant. Measure whether the top passages support generated answers.
Strengths and Limitations
Reranking can improve the order of useful candidates. It adds computation and can only work with items returned by the first stage.
Comparison with Similar Terms
A retriever finds candidates. A reranker reorders them. A grader evaluates a generated answer against a rubric.
Best Practices
Choose a candidate count that balances recall, latency, and cost. Track retrieval misses separately from ranking errors.
Common Pitfalls
Do not treat a high reranker score as proof of truth. If a needed document is absent from the candidate list, reranking cannot restore it.
FAQ
Does reranking replace the initial search?
No. It needs a first-stage retriever to supply candidates.