From 2550e46269b05aa89127b06c1e18d51ebadd9da3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?P=C3=A9ter=20Szil=C3=A1gyi?= <peterke@gmail.com>
Date: Fri, 26 Mar 2021 16:14:12 +0200
Subject: [PATCH] eth/protocols, metrics: use resetting histograms for rare
 packets

---
 eth/protocols/eth/handler.go  |  6 +++++-
 eth/protocols/snap/handler.go |  6 +++++-
 metrics/resetting_sample.go   | 24 ++++++++++++++++++++++++
 3 files changed, 34 insertions(+), 2 deletions(-)
 create mode 100644 metrics/resetting_sample.go

diff --git a/eth/protocols/eth/handler.go b/eth/protocols/eth/handler.go
index de5a38dcce98..0dc3de98982a 100644
--- a/eth/protocols/eth/handler.go
+++ b/eth/protocols/eth/handler.go
@@ -246,7 +246,11 @@ func handleMessage(backend Backend, peer *Peer) error {
 	if metrics.Enabled {
 		h := fmt.Sprintf("%s/%s/%d/%#02x", p2p.HandleHistName, ProtocolName, peer.Version(), msg.Code)
 		defer func(start time.Time) {
-			sampler := func() metrics.Sample { return metrics.NewExpDecaySample(1028, 0.015) }
+			sampler := func() metrics.Sample {
+				return metrics.ResettingSample(
+					metrics.NewExpDecaySample(1028, 0.015),
+				)
+			}
 			metrics.GetOrRegisterHistogramLazy(h, nil, sampler).Update(time.Since(start).Microseconds())
 		}(time.Now())
 	}
diff --git a/eth/protocols/snap/handler.go b/eth/protocols/snap/handler.go
index 6622cd871803..4169306c255f 100644
--- a/eth/protocols/snap/handler.go
+++ b/eth/protocols/snap/handler.go
@@ -134,7 +134,11 @@ func handleMessage(backend Backend, peer *Peer) error {
 	if metrics.Enabled {
 		h := fmt.Sprintf("%s/%s/%d/%#02x", p2p.HandleHistName, ProtocolName, peer.Version(), msg.Code)
 		defer func(start time.Time) {
-			sampler := func() metrics.Sample { return metrics.NewExpDecaySample(1028, 0.015) }
+			sampler := func() metrics.Sample {
+				return metrics.ResettingSample(
+					metrics.NewExpDecaySample(1028, 0.015),
+				)
+			}
 			metrics.GetOrRegisterHistogramLazy(h, nil, sampler).Update(time.Since(start).Microseconds())
 		}(time.Now())
 	}
diff --git a/metrics/resetting_sample.go b/metrics/resetting_sample.go
new file mode 100644
index 000000000000..43c1129cd0bc
--- /dev/null
+++ b/metrics/resetting_sample.go
@@ -0,0 +1,24 @@
+package metrics
+
+// ResettingSample converts an ordinary sample into one that resets whenever its
+// snapshot is retrieved. This will break for multi-monitor systems, but when only
+// a single metric is being pushed out, this ensure that low-frequency events don't
+// skew th charts indefinitely.
+func ResettingSample(sample Sample) Sample {
+	return &resettingSample{
+		Sample: sample,
+	}
+}
+
+// resettingSample is a simple wrapper around a sample that resets it upon the
+// snapshot retrieval.
+type resettingSample struct {
+	Sample
+}
+
+// Snapshot returns a read-only copy of the sample with the original reset.
+func (rs *resettingSample) Snapshot() Sample {
+	s := rs.Sample.Snapshot()
+	rs.Sample.Clear()
+	return s
+}