From 85abf6e46d9af25de811c59ef15e8320f6d6123c Mon Sep 17 00:00:00 2001
From: Geeta Gharpure <geetagh@amazon.com>
Date: Wed, 6 Oct 2021 11:01:07 -0700
Subject: [PATCH] storage/backend: Add a gauge to indicate if defrag is active
 (backport from 3.6)

---
 mvcc/backend/backend.go | 2 ++
 mvcc/backend/metrics.go | 8 ++++++++
 2 files changed, 10 insertions(+)

diff --git a/mvcc/backend/backend.go b/mvcc/backend/backend.go
index 523d358d5ae..4f12b9a6b34 100644
--- a/mvcc/backend/backend.go
+++ b/mvcc/backend/backend.go
@@ -354,6 +354,8 @@ func (b *backend) Defrag() error {
 
 func (b *backend) defrag() error {
 	now := time.Now()
+	isDefragActive.Set(1)
+	defer isDefragActive.Set(0)
 
 	// TODO: make this non-blocking?
 	// lock batchTx to ensure nobody is using previous tx, and then
diff --git a/mvcc/backend/metrics.go b/mvcc/backend/metrics.go
index d9641af7ae2..9d58c00638b 100644
--- a/mvcc/backend/metrics.go
+++ b/mvcc/backend/metrics.go
@@ -83,6 +83,13 @@ var (
 		// highest bucket start of 0.01 sec * 2^16 == 655.36 sec
 		Buckets: prometheus.ExponentialBuckets(.01, 2, 17),
 	})
+
+	isDefragActive = prometheus.NewGauge(prometheus.GaugeOpts{
+		Namespace: "etcd",
+		Subsystem: "disk",
+		Name:      "defrag_inflight",
+		Help:      "Whether or not defrag is active on the member. 1 means active, 0 means not.",
+	})
 )
 
 func init() {
@@ -92,4 +99,5 @@ func init() {
 	prometheus.MustRegister(writeSec)
 	prometheus.MustRegister(defragSec)
 	prometheus.MustRegister(snapshotTransferSec)
+	prometheus.MustRegister(isDefragActive)
 }