Add pool_name label to the gauges

This is kinda handy when you have more than 1 DB connection pool - for
example, when connecting to a cluster of N shards.

example/main.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"fmt"
 	"os"
 
 	"github.com/go-pg/pg/v9"
@@ -17,6 +18,9 @@ func main() {
 
 	db := pg.Connect(dbOpts)
 
+	// create unique pool name from DB address and database name
+	poolName := fmt.Printf("%s/%s", dbOpts.Addr, dbOpts.Database)
+
 	mon := monitor.NewMonitor(
 		// Observer package must match your go-pg version.
 		// E.g. for go-pg v10.x.x use package gopgv10.
@@ -31,6 +35,8 @@ func main() {
 			// my_app_go_pg_pool_hits{}
 			monitor.MetricsWithNamespace("my_app"),
 		),
+		// set pool name
+		monitor.MonitorWithPoolName(poolName),
 	)
 
 	mon.Open()

metrics.go

@@ -17,13 +17,13 @@ type Metrics struct {
 
 	constLabels prometheus.Labels
 
-	hits     prometheus.Gauge
-	misses   prometheus.Gauge
-	timeouts prometheus.Gauge
+	hits     *prometheus.GaugeVec
+	misses   *prometheus.GaugeVec
+	timeouts *prometheus.GaugeVec
 
-	totalConns prometheus.Gauge
-	idleConns  prometheus.Gauge
-	staleConns prometheus.Gauge
+	totalConns *prometheus.GaugeVec
+	idleConns  *prometheus.GaugeVec
+	staleConns *prometheus.GaugeVec
 
 	registerer prometheus.Registerer
 }
@@ -71,74 +71,80 @@ func NewMetrics(opts ...MetricsOption) *Metrics {
 		opt(m)
 	}
 
-	hits := prometheus.NewGauge(
+	hits := prometheus.NewGaugeVec(
 		prometheus.GaugeOpts{
 			Namespace:   m.namespace,
 			Subsystem:   m.subsystem,
 			ConstLabels: m.constLabels,
 			Name:        "pool_hits",
 			Help:        "Number of times free connection was found in the pool",
 		},
+		[]string{"pool_name"},
 	)
 	m.registerer.MustRegister(hits)
 	m.hits = hits
 
-	misses := prometheus.NewGauge(
+	misses := prometheus.NewGaugeVec(
 		prometheus.GaugeOpts{
 			Namespace:   m.namespace,
 			Subsystem:   m.subsystem,
 			ConstLabels: m.constLabels,
 			Name:        "pool_misses",
 			Help:        "Number of times free connection was NOT found in the pool",
 		},
+		[]string{"pool_name"},
 	)
 	m.registerer.MustRegister(misses)
 	m.misses = misses
 
-	timeouts := prometheus.NewGauge(
+	timeouts := prometheus.NewGaugeVec(
 		prometheus.GaugeOpts{
 			Namespace:   m.namespace,
 			Subsystem:   m.subsystem,
 			ConstLabels: m.constLabels,
 			Name:        "pool_timeouts",
 			Help:        "Number of times a wait timeout occurred",
 		},
+		[]string{"pool_name"},
 	)
 	m.registerer.MustRegister(timeouts)
 	m.timeouts = timeouts
 
-	totalConns := prometheus.NewGauge(
+	totalConns := prometheus.NewGaugeVec(
 		prometheus.GaugeOpts{
 			Namespace:   m.namespace,
 			Subsystem:   m.subsystem,
 			ConstLabels: m.constLabels,
 			Name:        "pool_total_connections",
 			Help:        "Number of total connections in the pool",
 		},
+		[]string{"pool_name"},
 	)
 	m.registerer.MustRegister(totalConns)
 	m.totalConns = totalConns
 
-	idleConns := prometheus.NewGauge(
+	idleConns := prometheus.NewGaugeVec(
 		prometheus.GaugeOpts{
 			Namespace:   m.namespace,
 			Subsystem:   m.subsystem,
 			ConstLabels: m.constLabels,
 			Name:        "pool_idle_connections",
 			Help:        "Number of idle connections in the pool",
 		},
+		[]string{"pool_name"},
 	)
 	m.registerer.MustRegister(idleConns)
 	m.idleConns = idleConns
 
-	staleConns := prometheus.NewGauge(
+	staleConns := prometheus.NewGaugeVec(
 		prometheus.GaugeOpts{
 			Namespace:   m.namespace,
 			Subsystem:   m.subsystem,
 			ConstLabels: m.constLabels,
 			Name:        "pool_stale_connections",
 			Help:        "Number of stale connections removed from the pool",
 		},
+		[]string{"pool_name"},
 	)
 	m.registerer.MustRegister(staleConns)
 	m.staleConns = staleConns

monitor.go

@@ -21,11 +21,20 @@ type Monitor struct {
 	wg     sync.WaitGroup
 	ctx    context.Context
 	cancel context.CancelFunc
+
+	poolName string
 }
 
 // MonitorOption is an option for NewMonitor.
 type MonitorOption func(monitor *Monitor)
 
+// MonitorWithPoolName is an option that sets pool name for the monitor.
+func MonitorWithPoolName(poolName string) MonitorOption { //nolint:golint
+	return func(monitor *Monitor) {
+		monitor.poolName = poolName
+	}
+}
+
 // NewMonitor returns a new configured Monitor.
 func NewMonitor(observer Observer, metrics *Metrics, opts ...MonitorOption) *Monitor {
 	m := &Monitor{
@@ -79,11 +88,11 @@ func (m *Monitor) worker() {
 func (m *Monitor) sync() {
 	stats := m.observer.Observe()
 
-	m.metrics.hits.Set(float64(stats.Hits))
-	m.metrics.misses.Set(float64(stats.Misses))
-	m.metrics.timeouts.Set(float64(stats.Timeouts))
+	m.metrics.hits.WithLabelValues(m.poolName).Set(float64(stats.Hits))
+	m.metrics.misses.WithLabelValues(m.poolName).Set(float64(stats.Misses))
+	m.metrics.timeouts.WithLabelValues(m.poolName).Set(float64(stats.Timeouts))
 
-	m.metrics.totalConns.Set(float64(stats.TotalConns))
-	m.metrics.idleConns.Set(float64(stats.IdleConns))
-	m.metrics.staleConns.Set(float64(stats.StaleConns))
+	m.metrics.totalConns.WithLabelValues(m.poolName).Set(float64(stats.TotalConns))
+	m.metrics.idleConns.WithLabelValues(m.poolName).Set(float64(stats.IdleConns))
+	m.metrics.staleConns.WithLabelValues(m.poolName).Set(float64(stats.StaleConns))
 }