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fix(opensearch): stop zeroing vector scores by mapping similarity to knn boost - #18662

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JinHai-CN merged 2 commits into
infiniflow:mainfrom
barandras:fix/vector-similarity-zero
Aug 24, 2026
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fix(opensearch): stop zeroing vector scores by mapping similarity to knn boost#18662
JinHai-CN merged 2 commits into
infiniflow:mainfrom
barandras:fix/vector-similarity-zero

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Summary

Fix OpenSearch retrieval returning vector_similarity = 0.000 for every chunk when hybrid search is enabled.

On the OpenSearch backend, retrieval uses a second KNN-only search (Dealer._knn_scores()) to recover per-chunk cosine scores for reranking. That pass intentionally sends MatchDenseExpr(..., {"similarity": 0.0}) to mean “no minimum similarity cutoff.”

However, OSConnection.search() was incorrectly mapping similarity to the KNN clause boost field:

knn_query[vector_column_name]["boost"] = similarity

With similarity=0.0, this produced boost=0.0, which zeroed out KNN _score values. get_scores() then returned 0.0 for every hit, so vector_similarity was always zero and hybrid ranking ignored the vector component — with no exception raised.

This is separate from the get_scores() AttributeError crash addressed in #14970 / #15390; here retrieval succeeds but vector scores are silently lost.

Root cause

  • similarity (threshold-like retrieval parameter) was conflated with boost (score multiplier).
  • The Elasticsearch connector does not set KNN boost this way; only OpenSearch did.
  • Existing OpenSearch unit tests validated hybrid query shape but not KNN score semantics.

Changes

  • rag/utils/opensearch_conn.py: Stop deriving KNN boost from similarity. Omit boost unless explicitly provided via MatchDenseExpr.extra_options["boost"].
  • test/unit_test/rag/utils/test_opensearch_hybrid_search.py: Add regression coverage:
    • KNN query omits boost when only similarity is set.
    • Explicit boost is still honored when provided.
    • Non-zero KNN _score values propagate unchanged through get_scores().

@dosubot dosubot Bot added size:XS This PR changes 0-9 lines, ignoring generated files. 🌈 python Pull requests that update Python code 🐞 bug Something isn't working, pull request that fix bug. 🧪 test Pull requests that update test cases. labels Aug 23, 2026
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Review Change Stack

No actionable comments were generated in the recent review. 🎉

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📒 Files selected for processing (2)
  • rag/utils/opensearch_conn.py
  • test/unit_test/rag/utils/test_opensearch_hybrid_search.py
🚧 Files skipped from review as they are similar to previous changes (2)
  • rag/utils/opensearch_conn.py
  • test/unit_test/rag/utils/test_opensearch_hybrid_search.py

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📝 Walkthrough

Walkthrough

OpenSearch KNN queries now include boost only when MatchDenseExpr.extra_options specifies it. Tests cover explicit and omitted boosts, plus unchanged nonzero score extraction.

Changes

KNN boost handling

Layer / File(s) Summary
Apply explicit KNN boosts
rag/utils/opensearch_conn.py
The search logic reads an optional explicit KNN boost and omits boost when none is provided.
Validate boost and score behavior
test/unit_test/rag/utils/test_opensearch_hybrid_search.py
Test helpers accept extra_options. Tests verify boost handling and unchanged nonzero score extraction.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to b5ddc

This change prevents OpenSearch vector scores from being zeroed during hybrid retrieval while preserving explicit boost settings and adding regression coverage; no actionable merge-blocking risk remains after normal checks and review.

Poem

I’m a rabbit with queries so neat,
No false boost hops under my feet.
Explicit boosts stay,
Scores keep their way,
And tests make the burrow complete.

🚥 Pre-merge checks | ✅ 5
✅ Passed checks (5 passed)
Check name Status Explanation
Title check ✅ Passed The title clearly and concisely describes the fix that prevents similarity from zeroing OpenSearch KNN vector scores.
Description check ✅ Passed The description includes the required Summary section and clearly explains the problem, root cause, changes, and regression tests.
Docstring Coverage ✅ Passed Docstring check was indeterminate for this PR — some files could not be analyzed in time. Not blocking.
Linked Issues check ✅ Passed Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check ✅ Passed Check skipped because no linked issues were found for this pull request.

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Actionable comments posted: 1

🧹 Nitpick comments (1)
rag/utils/opensearch_conn.py (1)

416-417: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick win

Add safe debug logging for the explicit-boost path.

The query log at Line 449 runs before the KNN or hybrid query is assembled, so it does not show the boost added here. Add structured debug metadata such as whether an explicit boost was supplied and its value. Do not log the final query body because it contains embedding data.

As per coding guidelines, **/*.py: Add logging for new flows.

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In `@rag/utils/opensearch_conn.py` around lines 416 - 417, Update the
explicit_boost handling near the KNN query construction to emit structured debug
metadata indicating whether an explicit boost was supplied and, when present,
its value. Place the log after the boost is applied so it reflects this path,
and log only boost metadata rather than the assembled query body or embedding
data.

Source: Coding guidelines

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only still-valid issues, skip the rest with a brief reason, keep changes
minimal, and validate.

Inline comments:
In `@rag/utils/opensearch_conn.py`:
- Around line 401-403: Remove the obsolete similarity access immediately before
the guarded boost handling in the dense-expression processing path, ensuring
extra_options=None reaches the boost logic without raising TypeError. Add a
regression test covering MatchDenseExpr with extra_options=None and verify the
search path completes successfully.

---

Nitpick comments:
In `@rag/utils/opensearch_conn.py`:
- Around line 416-417: Update the explicit_boost handling near the KNN query
construction to emit structured debug metadata indicating whether an explicit
boost was supplied and, when present, its value. Place the log after the boost
is applied so it reflects this path, and log only boost metadata rather than the
assembled query body or embedding data.
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Reviewing files that changed from the base of the PR and between 9ea83b7 and 7f29362.

📒 Files selected for processing (2)
  • rag/utils/opensearch_conn.py
  • test/unit_test/rag/utils/test_opensearch_hybrid_search.py

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Comment thread rag/utils/opensearch_conn.py
…options=None

The leftover `"similarity" in extra_options` check raised TypeError when
extra_options was None. The test helper treated None as a default dict, so
use a sentinel so the regression case can pass None through.
@barandras
barandras force-pushed the fix/vector-similarity-zero branch from 7f29362 to b5ddc08 Compare August 23, 2026 14:26
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GitHub couldn't provide a complete incremental comparison for this pull request, so CodeRabbit is performing a full review instead. This review may take a little longer.

@qinling0210 qinling0210 added the ci Continue Integration label Aug 24, 2026
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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.65%. Comparing base (2db8eb6) to head (b5ddc08).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files
@@            Coverage Diff             @@
##             main   #18662      +/-   ##
==========================================
- Coverage   94.56%   90.65%   -3.91%     
==========================================
  Files          10       10              
  Lines         717      717              
  Branches      118      118              
==========================================
- Hits          678      650      -28     
- Misses         25       39      +14     
- Partials       14       28      +14     

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LGTM

@JinHai-CN
JinHai-CN merged commit 7c455fb into infiniflow:main Aug 24, 2026
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