From bed85a0642d8d99c6f1eae02b7659da4ea7f03ad Mon Sep 17 00:00:00 2001
From: Aaron Beitch <aaronb@arista.com>
Date: Mon, 30 Dec 2024 16:07:06 -0800
Subject: [PATCH] Add metric for number of active scanner renewers

This can be used to identify scanner leaks.
---
 prometheus.go | 8 ++++++++
 scanner.go    | 6 +++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/prometheus.go b/prometheus.go
index 76ef540e..62eb1ea3 100644
--- a/prometheus.go
+++ b/prometheus.go
@@ -53,4 +53,12 @@ var (
 			4.096, 8.192, 13.192, 18.192, 23.192, 28.192, 33.192,
 		},
 	})
+
+	scanRenewers = promauto.NewGauge(prometheus.GaugeOpts{
+		Namespace: "gohbase",
+		Subsystem: "scanner",
+		Name:      "renewer_count",
+		Help: "Number of active scanner renewers. " +
+			"A continually increasing value indicates an Scanner leak.",
+	})
 )
diff --git a/scanner.go b/scanner.go
index defcbbd4..d1c445bf 100644
--- a/scanner.go
+++ b/scanner.go
@@ -401,8 +401,12 @@ func (s *scanner) renew(ctx context.Context, startRow []byte) error {
 }
 
 func (s *scanner) renewLoop(ctx context.Context, startRow []byte) {
+	scanRenewers.Inc()
 	t := time.NewTicker(s.rpc.RenewInterval())
-	defer t.Stop()
+	defer func() {
+		t.Stop()
+		scanRenewers.Dec()
+	}()
 
 	for {
 		select {