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feat: Add reciprocal rank fusion to MultiRetriever#11220

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sjrl merged 5 commits intomainfrom
add-rrf-multi-retriever
Apr 30, 2026
Merged

feat: Add reciprocal rank fusion to MultiRetriever#11220
sjrl merged 5 commits intomainfrom
add-rrf-multi-retriever

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@sjrl sjrl commented Apr 29, 2026 •
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Related Issues

Proposed Changes:

Add join_mode param to MultiRetriever like in DocumentJoiner with the default set to rank and de-duplicate via reciprocal rank fusion. Makes the component's runs more consistent and reproducible and produces a decent ranking without needing to specify any additional rankers. RRF must be baked in and can't be done downstream b/c the returned list is flattened so the info needed for RRF is lost.

Created new util method to reuse in both components

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Added new unit tests

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  • I have added unit tests and updated the docstrings.
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@sjrl sjrl requested a review from a team as a code owner April 29, 2026 13:22
@sjrl sjrl requested review from bogdankostic and removed request for a team April 29, 2026 13:22
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vercel Bot commented Apr 29, 2026 •
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sjrl commented Apr 29, 2026

cc @julian-risch

@sjrl sjrl self-assigned this Apr 29, 2026
@github-actions github-actions Bot added topic:tests type:documentation Improvements on the docs labels Apr 29, 2026
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github-actions Bot commented Apr 29, 2026 •
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Coverage report

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FileStatementsMissingCoverageCoverage
(new stmts)		Lines missing
  haystack/components/joiners
  document_joiner.py
  haystack/components/retrievers
  multi_retriever.py 122
  haystack/utils
  misc.py
Project Total  

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claude Bot commented Apr 29, 2026

Code review

No issues found. Checked for bugs and CLAUDE.md compliance.

bogdankostic
bogdankostic reviewed Apr 30, 2026
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Looking good in general, let's just distinguish the same name _reciprocal_rank_fusion for the utility function and the method of DocumentJoiner.

Also, in DocumentJoiner we allow to set weights for the different retrieval results, should we support that for MultiRetriever as well?

Comment thread haystack/components/joiners/document_joiner.py Outdated
@@ -196,32 +197,8 @@ def _merge(self, document_lists: list[list[Document]]) -> list[Document]:
def _reciprocal_rank_fusion(self, document_lists: list[list[Document]]) -> list[Document]:
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The name of the method shadows the name of the imported utility function, maybe we can have different names for both for better readability?

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@sjrl sjrl Apr 30, 2026

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Done in 0800212

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sjrl commented Apr 30, 2026

Also, in DocumentJoiner we allow to set weights for the different retrieval results, should we support that for MultiRetriever as well?

I think it's fine to leave out for now and we can add it later if people ask for it. I expect that most users will be sending these docs downstream to a ranker component anyways.

@sjrl sjrl requested a review from bogdankostic April 30, 2026 11:09
bogdankostic
bogdankostic approved these changes Apr 30, 2026
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LGTM

@sjrl sjrl merged commit 744198c into main Apr 30, 2026
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@sjrl sjrl deleted the add-rrf-multi-retriever branch April 30, 2026 11:33
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