Improve xpub cache

common/metrics.go

@@ -32,6 +32,7 @@ type Metrics struct {
 	ExplorerPendingRequests  *prometheus.GaugeVec
 	WebsocketPendingRequests *prometheus.GaugeVec
 	SocketIOPendingRequests  *prometheus.GaugeVec
+	XPubCacheSize            prometheus.Gauge
 }
 
 // Labels represents a collection of label name -> value mappings.
@@ -230,6 +231,13 @@ func GetMetrics(coin string) (*Metrics, error) {
 		},
 		[]string{"method"},
 	)
+	metrics.XPubCacheSize = prometheus.NewGauge(
+		prometheus.GaugeOpts{
+			Name:        "blockbook_xpub_cache_size",
+			Help:        "Number of cached xpubs",
+			ConstLabels: Labels{"coin": coin},
+		},
+	)
 
 	v := reflect.ValueOf(metrics)
 	for i := 0; i < v.NumField(); i++ {