monitoring: add dbsize collector

monitoring/db_collector.go

@@ -0,0 +1,81 @@
+package monitoring
+
+import (
+	"context"
+	"errors"
+	"sync"
+
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+const (
+	dbSizeMetric = "total_db_size"
+)
+
+// dbCollector is a Prometheus collector that exports metrics related to the
+// daemon's database.
+type dbCollector struct {
+	collectMx sync.Mutex
+
+	cfg      *PrometheusConfig
+	registry *prometheus.Registry
+
+	dbSize prometheus.Gauge
+}
+
+func newDbCollector(cfg *PrometheusConfig,
+	registry *prometheus.Registry) (*dbCollector, error) {
+
+	if cfg == nil {
+		return nil, errors.New("db collector prometheus cfg is nil")
+	}
+
+	if cfg.AssetStore == nil {
+		return nil, errors.New("db collector asset store is nil")
+	}
+
+	return &dbCollector{
+		cfg:      cfg,
+		registry: registry,
+		dbSize: prometheus.NewGauge(
+			prometheus.GaugeOpts{
+				Name: dbSizeMetric,
+				Help: "Total size of db",
+			},
+		),
+	}, nil
+}
+
+// Describe sends the super-set of all possible descriptors of metrics
+// collected by this Collector to the provided channel and returns once the
+// last descriptor has been sent.
+//
+// NOTE: Part of the prometheus.Collector interface.
+func (a *dbCollector) Describe(ch chan<- *prometheus.Desc) {
+	a.collectMx.Lock()
+	defer a.collectMx.Unlock()
+
+	a.dbSize.Describe(ch)
+}
+
+// Collect is called by the Prometheus registry when collecting metrics.
+//
+// NOTE: Part of the prometheus.Collector interface.
+func (a *dbCollector) Collect(ch chan<- prometheus.Metric) {
+	a.collectMx.Lock()
+	defer a.collectMx.Unlock()
+
+	ctxdb, cancel := context.WithTimeout(context.Background(), dbTimeout)
+	defer cancel()
+
+	// Fetch the db size.
+	dbSize, err := a.cfg.AssetStore.AssetsDBSize(ctxdb)
+	if err != nil {
+		log.Errorf("unable to fetch db size: %v", err)
+		return
+	}
+
+	a.dbSize.Set(float64(dbSize))
+
+	a.dbSize.Collect(ch)
+}

monitoring/prometheus.go

@@ -74,6 +74,12 @@ func (p *PrometheusExporter) Start() error {
 	}
 	p.registry.MustRegister(gardenCollector)
 
+	dbCollector, err := newDbCollector(p.config, p.registry)
+	if err != nil {
+		return err
+	}
+	p.registry.MustRegister(dbCollector)
+
 	assetProofCollector, err := newAssetProofCollector(p.config, p.registry)
 	if err != nil {
 		return err