[hw-7] add metrics, tracing

loms/internal/infra/grpc/metrics/db.go

@@ -0,0 +1,31 @@
+package metrics
+
+import (
+	"time"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+)
+
+var (
+	dbQueryCounter = promauto.NewCounterVec(prometheus.CounterOpts{
+		Namespace: "app",
+		Name:      "db_queries_total",
+		Help:      "Total DB queries",
+	}, []string{"category", "error"})
+
+	dbQueryDurationHistogram = promauto.NewHistogramVec(prometheus.HistogramOpts{
+		Namespace: "app",
+		Name:      "db_query_duration_seconds",
+		Help:      "Latency of DB queries, seconds",
+		Buckets:   prometheus.DefBuckets,
+	}, []string{"category", "error"})
+)
+
+func IncDBQueryCount(cat, errLabel string) {
+	dbQueryCounter.WithLabelValues(cat, errLabel).Inc()
+}
+
+func StoreDBQueryDuration(cat, errLabel string, d time.Duration) {
+	dbQueryDurationHistogram.WithLabelValues(cat, errLabel).Observe(d.Seconds())
+}