redisbp: Change stale connections metrics to counter

It's actually implemented as a counter under the hood (with atomic adds
on uint32 values), not a gauge.

redis/db/redisbp/prometheus.go

@@ -40,6 +40,12 @@ var (
 		promLabels,
 		nil,
 	)
+	staleConnectionsCounterDesc = prometheus.NewDesc(
+		prometheus.BuildFQName(promNamespace, subsystemPool, "stale_connections_total"),
+		"Number of stale connections removed from this redisbp pool",
+		promLabels,
+		nil,
+	)
 
 	// Gauges.
 	totalConnectionsDesc = prometheus.NewDesc(
@@ -54,12 +60,6 @@ var (
 		promLabels,
 		nil,
 	)
-	staleConnectionsDesc = prometheus.NewDesc(
-		prometheus.BuildFQName(promNamespace, subsystemPool, "stale_connections"),
-		"Number of stale connections in this redisbp pool",
-		promLabels,
-		nil,
-	)
 )
 
 var (
@@ -111,6 +111,12 @@ func (e exporter) Collect(ch chan<- prometheus.Metric) {
 		float64(stats.Timeouts),
 		e.name,
 	)
+	ch <- prometheus.MustNewConstMetric(
+		staleConnectionsCounterDesc,
+		prometheus.CounterValue,
+		float64(stats.StaleConns),
+		e.name,
+	)
 
 	// Gauges.
 	ch <- prometheus.MustNewConstMetric(
@@ -125,10 +131,4 @@ func (e exporter) Collect(ch chan<- prometheus.Metric) {
 		float64(stats.IdleConns),
 		e.name,
 	)
-	ch <- prometheus.MustNewConstMetric(
-		staleConnectionsDesc,
-		prometheus.GaugeValue,
-		float64(stats.StaleConns),
-		e.name,
-	)
 }