Data & RAG14 September 2026·5 min read

Reranking: when a second pass is worth the extra latency

A reranker reorders retrieved passages by relevance. It often helps accuracy, and it always adds time and cost. How to decide.

First-stage retrieval is fast but approximate. A reranker examines the shortlisted passages more carefully and reorders them, so the best evidence reaches the model.

Consider it when

The right passage is retrieved but ranked too low.
Documents are long, similar or ambiguous.
Answer accuracy matters more than response speed.

Be cautious when

Latency is tight and the first stage is already accurate.
The corpus is small and distinct.
You haven't measured retrieval quality yet.

Measure whether the correct source appears in the top results before and after. Add the reranker only if the measured gain covers its cost.

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