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docs(quantization): soften multi-bit RaBitQ cost framing, add cross-version note#284

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docs/rabitq-multibit-cost-framing
Jun 25, 2026
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docs(quantization): soften multi-bit RaBitQ cost framing, add cross-version note#284
prrao87 merged 1 commit into
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docs/rabitq-multibit-cost-framing

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@prrao87 prrao87 commented Jun 25, 2026

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What

Updates the RaBitQ section of the quantization docs in light of lance#7205, which added dedicated SIMD kernels for multi-bit (num_bits >= 2) RaBitQ ex-code reranking.

  • Soften the multi-bit cost framing. The docs previously steered users away from num_bits >= 2 on a "higher computational cost" basis. With the new SIMD rerank kernels, that's outdated — the real trade-off is storage. Reworded both the prose and the num_bits parameter description accordingly.
  • Add a cross-version compatibility warning. Multi-bit indexes use an updated on-disk layout that older LanceDB versions cannot read (loud missing-column error, not silent corruption). Existing indexes keep working and upgrade automatically on rewrite; num_bits=1 is unaffected in both directions.
  • Move the ## API Reference heading below the conceptual prose so it sits directly above the parameter list it introduces (it previously sat above the explanatory text, which read oddly).

Why

This is the durable, user-facing residue of the lance perf work — not a "we got faster" announcement (that belongs in release notes), but a correction to framing that would otherwise steer people away from multi-bit on outdated grounds, plus the one piece with real user impact: the version-compatibility break.

Notes

  • Assumes the new on-disk format ships with the upcoming LanceDB release (lance core is vendored into the latest LanceDB).
  • Used <Warning> rather than the page's usual <Note> deliberately — a breaking-compat item warrants the higher severity styling.

🤖 Generated with Claude Code

…ersion note

Multi-bit RaBitQ (num_bits >= 2) reranking now uses dedicated SIMD
kernels, so the prior framing that steered users away from num_bits >= 2
on a compute basis is outdated. The real trade-off is storage.

- Reframe the num_bits prose and param description around storage cost
  rather than "higher computational cost".
- Add a compatibility warning: multi-bit indexes use an updated on-disk
  layout that older LanceDB versions cannot read; existing indexes
  upgrade on rewrite, num_bits=1 is unaffected.
- Move the "API Reference" heading below the conceptual prose so it sits
  directly above the parameter list it introduces.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
@prrao87 prrao87 added the needs_new_release Only merge once we release a new version of LanceDB label Jun 25, 2026
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@prrao87 prrao87 merged commit add375f into main Jun 25, 2026
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@prrao87 prrao87 deleted the docs/rabitq-multibit-cost-framing branch June 25, 2026 13:25
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