Base SQL metrics in MetricsWorker (#2002)

* feat: Add metrics worker

* refactor: Add todos for useful for metrics methods

* feat: Run MetricsWorker is Prometheus is Enabled

* refactor: Unused low-level variable was removed in metrics

* feat: No worker for metrics, add more

* refactor: Unnecessary todo removed

* refactor: Remove dead unused constant

* Reduce metrics public interface

Co-authored-by: Deluan <deluan@navidrome.org>

cmd/root.go

@@ -10,6 +10,7 @@ import (
 
 	"github.com/navidrome/navidrome/conf"
 	"github.com/navidrome/navidrome/consts"
+	"github.com/navidrome/navidrome/core"
 	"github.com/navidrome/navidrome/db"
 	"github.com/navidrome/navidrome/log"
 	"github.com/navidrome/navidrome/resources"
@@ -91,6 +92,8 @@ func startServer(ctx context.Context) func() error {
 			a.MountRouter("ListenBrainz Auth", consts.URLPathNativeAPI+"/listenbrainz", CreateListenBrainzRouter())
 		}
 		if conf.Server.Prometheus.Enabled {
+			// blocking call because takes <1ms but useful if fails
+			core.WriteInitialMetrics()
 			a.MountRouter("Prometheus metrics", conf.Server.Prometheus.MetricsPath, promhttp.Handler())
 		}
 		if strings.HasPrefix(conf.Server.UILoginBackgroundURL, "/") {

core/metrics.go

@@ -0,0 +1,123 @@
+package core
+
+import (
+	"context"
+	"fmt"
+	"strconv"
+	"sync"
+
+	"github.com/navidrome/navidrome/consts"
+	"github.com/navidrome/navidrome/log"
+	"github.com/navidrome/navidrome/model"
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+func WriteInitialMetrics() {
+	getPrometheusMetrics().versionInfo.With(prometheus.Labels{"version": consts.Version}).Set(1)
+}
+
+func WriteAfterScanMetrics(ctx context.Context, dataStore model.DataStore, success bool) {
+	processSqlAggregateMetrics(ctx, dataStore, getPrometheusMetrics().dbTotal)
+
+	scanLabels := prometheus.Labels{"success": strconv.FormatBool(success)}
+	getPrometheusMetrics().lastMediaScan.With(scanLabels).SetToCurrentTime()
+	getPrometheusMetrics().mediaScansCounter.With(scanLabels).Inc()
+}
+
+// Prometheus' metrics requires initialization. But not more than once
+var (
+	prometheusMetricsInstance *prometheusMetrics
+	prometheusOnce            sync.Once
+)
+
+type prometheusMetrics struct {
+	dbTotal           *prometheus.GaugeVec
+	versionInfo       *prometheus.GaugeVec
+	lastMediaScan     *prometheus.GaugeVec
+	mediaScansCounter *prometheus.CounterVec
+}
+
+func getPrometheusMetrics() *prometheusMetrics {
+	prometheusOnce.Do(func() {
+		var err error
+		prometheusMetricsInstance, err = newPrometheusMetrics()
+		if err != nil {
+			log.Fatal("Unable to create Prometheus metrics instance.", err)
+		}
+	})
+	return prometheusMetricsInstance
+}
+
+func newPrometheusMetrics() (*prometheusMetrics, error) {
+	res := &prometheusMetrics{
+		dbTotal: prometheus.NewGaugeVec(
+			prometheus.GaugeOpts{
+				Name: "db_model_totals",
+				Help: "Total number of DB items per model",
+			},
+			[]string{"model"},
+		),
+		versionInfo: prometheus.NewGaugeVec(
+			prometheus.GaugeOpts{
+				Name: "navidrome_info",
+				Help: "Information about Navidrome version",
+			},
+			[]string{"version"},
+		),
+		lastMediaScan: prometheus.NewGaugeVec(
+			prometheus.GaugeOpts{
+				Name: "media_scan_last",
+				Help: "Last media scan timestamp by success",
+			},
+			[]string{"success"},
+		),
+		mediaScansCounter: prometheus.NewCounterVec(
+			prometheus.CounterOpts{
+				Name: "media_scans",
+				Help: "Total success media scans by success",
+			},
+			[]string{"success"},
+		),
+	}
+
+	err := prometheus.DefaultRegisterer.Register(res.dbTotal)
+	if err != nil {
+		return nil, fmt.Errorf("unable to register db_model_totals metrics: %w", err)
+	}
+	err = prometheus.DefaultRegisterer.Register(res.versionInfo)
+	if err != nil {
+		return nil, fmt.Errorf("unable to register navidrome_info metrics: %w", err)
+	}
+	err = prometheus.DefaultRegisterer.Register(res.lastMediaScan)
+	if err != nil {
+		return nil, fmt.Errorf("unable to register media_scan_last metrics: %w", err)
+	}
+	err = prometheus.DefaultRegisterer.Register(res.mediaScansCounter)
+	if err != nil {
+		return nil, fmt.Errorf("unable to register media_scans metrics: %w", err)
+	}
+	return res, nil
+}
+
+func processSqlAggregateMetrics(ctx context.Context, dataStore model.DataStore, targetGauge *prometheus.GaugeVec) {
+	albumsCount, err := dataStore.Album(ctx).CountAll()
+	if err != nil {
+		log.Warn("album CountAll error", err)
+		return
+	}
+	targetGauge.With(prometheus.Labels{"model": "album"}).Set(float64(albumsCount))
+
+	songsCount, err := dataStore.MediaFile(ctx).CountAll()
+	if err != nil {
+		log.Warn("media CountAll error", err)
+		return
+	}
+	targetGauge.With(prometheus.Labels{"model": "media"}).Set(float64(songsCount))
+
+	usersCount, err := dataStore.User(ctx).CountAll()
+	if err != nil {
+		log.Warn("user CountAll error", err)
+		return
+	}
+	targetGauge.With(prometheus.Labels{"model": "user"}).Set(float64(usersCount))
+}

model/player.go

@@ -24,4 +24,5 @@ type PlayerRepository interface {
 	Get(id string) (*Player, error)
 	FindMatch(userName, client, typ string) (*Player, error)
 	Put(p *Player) error
+	// TODO: Add CountAll method. Useful at least for metrics.
 }

scanner/scanner.go

@@ -151,8 +151,10 @@ func (s *scanner) RescanAll(ctx context.Context, fullRescan bool) error {
 	}
 	if hasError {
 		log.Error("Errors while scanning media. Please check the logs")
+		core.WriteAfterScanMetrics(ctx, s.ds, false)
 		return ErrScanError
 	}
+	core.WriteAfterScanMetrics(ctx, s.ds, true)
 	return nil
 }