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Dify version

0.5.10

Cloud or Self Hosted

Self Hosted (Docker)

Steps to reproduce

enable the rerank model, and set threshold value and topk value, debug the recall behavior.

✔️ Expected Behavior

topk and threshold value should only affect rerank stage, like the doc describes.
(sorry, I didn't find this explaination in English doc...)

the last line words says, the topk and threshold value will only affect the rerank stage.
(there is another doubt, somehow, I assume that dify has a mechanism that recall a limited item set from vectordb and send them to rerank stage)
so the RAG with rerank steps will be like:
sim search and get a bunch of doc chunks ==> somehow? to get n (n>k) chunks ==> rerank stage ==> filtered by the treshold
==> get top-k from reordered and filtered chunk list ==> got final reference

❌ Actual Behavior

from the code, seems the recall logic use topk and threshold both in the first retrival and rerank stage.
so current RAG with rerank steps are:
sim search ==> filtered by threshold and get top-k chunks ==> rerank stage to get reodered chunk list ==> again, filtered by threshold and get top-k chunks ==> got final reference
I think reranking chunks within the top-k chunks got from the first retrival stage is kind of meaningless, if user always tend to use very small top-k value like 2, 3... there is no meaning for reranking with in this kind of small chunk set.
what do you think?