From 1fd64aa8dc68d7efb3fcd3859d3508f62280c6d8 Mon Sep 17 00:00:00 2001
From: Spetrum <11692994+Septrum101@users.noreply.github.com>
Date: Wed, 10 Jun 2026 11:36:45 +0800
Subject: [PATCH] Prevent caching of responses resolved via fallback

---
 proxy/optimisticresolver.go | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/proxy/optimisticresolver.go b/proxy/optimisticresolver.go
index 011ade64d..c4a4138c2 100644
--- a/proxy/optimisticresolver.go
+++ b/proxy/optimisticresolver.go
@@ -62,7 +62,11 @@ func (s *optimisticResolver) resolveOnce(dctx *DNSContext, key []byte, l *slog.L
 		l.Debug("resolving request for optimistic cache", slogutil.KeyError, err)
 	}
 
-	if ok {
+	if ok && !resolvedByFallback(dctx) {
 		s.cr.cacheResp(dctx)
 	}
 }
+
+func resolvedByFallback(dctx *DNSContext) (ok bool) {
+	return dctx.queryStatistics != nil && len(dctx.queryStatistics.Fallback()) > 0
+}