From 1785fcf02896b37e40cc0ff476d14916251e841b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Piotr=20Wo=CC=81jcik?=
 <3044353+pwojcikdev@users.noreply.github.com>
Date: Sat, 4 Jan 2025 13:48:55 +0100
Subject: [PATCH] Warn about large backlog of notifications

---
 nano/lib/stats_enums.hpp    |  1 +
 nano/node/rpc_callbacks.cpp | 10 ++++++++++
 2 files changed, 11 insertions(+)

diff --git a/nano/lib/stats_enums.hpp b/nano/lib/stats_enums.hpp
index 630e0d1ea0..752b49081a 100644
--- a/nano/lib/stats_enums.hpp
+++ b/nano/lib/stats_enums.hpp
@@ -638,6 +638,7 @@ enum class detail
 
 	// http_callbacks
 	block_confirmed,
+	large_backlog,
 
 	_last // Must be the last enum
 };
diff --git a/nano/node/rpc_callbacks.cpp b/nano/node/rpc_callbacks.cpp
index cb1a0be4f2..9fa05802c5 100644
--- a/nano/node/rpc_callbacks.cpp
+++ b/nano/node/rpc_callbacks.cpp
@@ -1,4 +1,5 @@
 #include <nano/lib/block_type.hpp>
+#include <nano/lib/interval.hpp>
 #include <nano/node/node.hpp>
 #include <nano/node/rpc_callbacks.hpp>
 #include <nano/secure/ledger.hpp>
@@ -51,6 +52,15 @@ void nano::http_callbacks::setup_callbacks ()
 		{
 			stats.inc (nano::stat::type::http_callbacks_notified, nano::stat::detail::block_confirmed);
 
+			constexpr size_t warning_threshold = 10000;
+			static nano::interval warning_interval;
+
+			if (workers.queued_tasks () > warning_threshold && warning_interval.elapsed (15s))
+			{
+				stats.inc (nano::stat::type::http_callbacks, nano::stat::detail::large_backlog);
+				logger.warn (nano::log::type::http_callbacks, "Backlog of {} http callback notifications to process", workers.queued_tasks ());
+			}
+
 			// Post callback processing to worker thread
 			// Safe to capture 'this' by reference as workers are stopped before this component destruction
 			workers.post ([this, block_a, account_a, amount_a, is_state_send_a, is_state_epoch_a] () {