From 6fadd0e2ee92cfa876c6406280ee34b40a2c062d Mon Sep 17 00:00:00 2001
From: Pratik Mankawde <3397372+pratikmankawde@users.noreply.github.com>
Date: Wed, 23 Sep 2026 13:49:54 +0100
Subject: [PATCH] fix(telemetry): emit consensus.mode_change only on a real
 transition

MonitoredMode::set calls onModeChange on every round start, so the span was
created whether or not the mode moved. A node with a steady mode therefore
emitted one mode_change per round carrying mode_old == mode_new, which a live
sweep confirmed on every round of both instrumented builds. The round span's
own consensus_mode attribute is still written on every call, since that is
where the round learns the mode it is running in.
---
 include/xrpl/consensus/ConsensusSpanNames.h |  2 +-
 src/xrpld/app/consensus/RCLConsensus.cpp    | 13 ++++++++++---
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/include/xrpl/consensus/ConsensusSpanNames.h b/include/xrpl/consensus/ConsensusSpanNames.h
index 46935294e8..db649443a4 100644
--- a/include/xrpl/consensus/ConsensusSpanNames.h
+++ b/include/xrpl/consensus/ConsensusSpanNames.h
@@ -73,7 +73,7 @@
  *    |     Attrs:   ledger_seq, proposing
  *    |
  *    +-- consensus.mode_change                   [main thread]
- *          Created: Adaptor::onModeChange()
+ *          Created: Adaptor::onModeChange(), only when the mode moves
  *          Attrs:   mode_old, mode_new
  *
  *  Standalone spans (no parent, created per-message in overlay):
diff --git a/src/xrpld/app/consensus/RCLConsensus.cpp b/src/xrpld/app/consensus/RCLConsensus.cpp
index c08839c6a0..c1d2834653 100644
--- a/src/xrpld/app/consensus/RCLConsensus.cpp
+++ b/src/xrpld/app/consensus/RCLConsensus.cpp
@@ -1135,9 +1135,16 @@ RCLConsensus::Adaptor::onModeChange(ConsensusMode before, ConsensusMode after)
     // thread-free SpanGuard, so parent explicitly via its context). A mode
     // change outside a round leaves roundSpanContext_ invalid, yielding a null
     // guard (no-op).
-    auto span = telemetry::SpanGuard::childSpan(cs::modeChange, roundSpanContext_);
-    span.setAttribute(cs::attr::modeOld, toDisplayString(before).c_str());
-    span.setAttribute(cs::attr::modeNew, toDisplayString(after).c_str());
+    //
+    // Only a real transition gets a span. MonitoredMode::set also calls this
+    // on every round start; the round's mode attribute below still needs that
+    // call, the span does not.
+    if (before != after)
+    {
+        auto span = telemetry::SpanGuard::childSpan(cs::modeChange, roundSpanContext_);
+        span.setAttribute(cs::attr::modeOld, toDisplayString(before).c_str());
+        span.setAttribute(cs::attr::modeNew, toDisplayString(after).c_str());
+    }
 
     JLOG(j_.info()) << "Consensus mode change before=" << to_string(before)
                     << ", after=" << to_string(after);