From 807e57aa3456c30da740e124cd68f864bb733ca8 Mon Sep 17 00:00:00 2001
From: zhangruijie <2542201615@qq.com>
Date: Thu, 11 Jun 2026 18:46:15 +0800
Subject: [PATCH] =?UTF-8?q?feat:=20rerank=20=E4=B8=8D=E5=8F=AF=E7=94=A8?=
 =?UTF-8?q?=E6=97=B6=E9=99=8D=E7=BA=A7=E5=88=B0=20RRF=20=E7=AE=97=E6=B3=95?=
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远程 rerank 服务失败时，NewRerank 不再透传 error，
改为打 Warning 日志并降级调用 rrfFallback，保证检索链路可用。

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
---
 server/core/rerank/rerank.go | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/server/core/rerank/rerank.go b/server/core/rerank/rerank.go
index b1b8622..9a55682 100644
--- a/server/core/rerank/rerank.go
+++ b/server/core/rerank/rerank.go
@@ -46,9 +46,23 @@ var rerankCfg *Conf
 func NewRerank(ctx context.Context, query string, docs []*schema.Document, topK int) (output []*schema.Document, err error) {
 	output, err = rerank(ctx, query, docs, topK)
 	if err != nil {
-		return
+		g.Log().Warningf(ctx, "Rerank remote failed, fallback to RRF: %v", err)
+		return rrfFallback(docs, topK), nil
 	}
-	return
+	return output, nil
+}
+
+// rrfFallback 用 RRF 算法对单路结果（已按原始 score 排好序）重新打分并截断到 topK。
+// 单路 RRF 本质上保持原顺序，但把分数统一到可比较的 1/(k+rank) 量纲。
+func rrfFallback(docs []*schema.Document, topK int) []*schema.Document {
+	const k = 60
+	for rank, doc := range docs {
+		doc.WithScore(1.0 / float64(k+rank+1))
+	}
+	if topK > 0 && len(docs) > topK {
+		return docs[:topK]
+	}
+	return docs
 }
 
 func GetConf(ctx context.Context) *Conf {