[jamesgao-jpg]

Summary

Add a server-controlled multiplier for the optional full-dimensional MRL rerank.

• Configure it with KnowhereConfig::SetMRLRefineRatio, not request JSON or serialized index metadata.
• With MRL refinement enabled, retrieve int(topk * ratio) prefix-index results, rerank those IDs using full-dimensional raw vectors, and return the original topk.
• Use DVR's truncating conversion, guard integer overflow, default to 1.0, and reject non-finite values or values below 1.
• Ignore the ratio when MRL refinement is disabled.
• Keep SCANN's inner reorder count at least as large as the expanded requested result count. Ordinary request validation is unchanged.

Related issue and dependencies

issue: #1850

PR #1849 introduced the MRL wrapper. PR #1884 added nullable-ID mapping and search-scoped raw-data views; both have merged.

Milvus PR milvus-io/milvus#53822 initializes this setting from server configuration at QueryNode startup.

This draft is based on merged MRL revision 549a4367a8b0b61e7ad7c2978b93fdfe7af9cbf0. The later nullable API migration in PR #1890 remains separate from the accompanying Milvus dependency pin.

Validation

On the configured arm64 development machine:

• CPU unit-test build completed.
• [mrl]: 126 assertions passed across 9 test cases, including the SCANN regression.
• FLAT/HNSW coverage includes truncation, full-dimensional neighbor recovery, filtering, reload, disabled refinement, and overflow rejection.
• Nullable-ID mapping and per-search raw-data scope tests passed.
• Request-level ratio values cannot change the server setting.
• Pre-commit formatting and whitespace checks passed.

This remains a draft for additional MRL/DVR refactors as they are agreed.

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