Add events_read_total metric

Author: inelpandzic

metrics/metrics.go

@@ -11,6 +11,13 @@ const metricNamespace = "percona_clustersync_mongodb"
 
 // Counters.
 var (
+	//nolint:gochecknoglobals
+	eventsReadTotal = prometheus.NewCounter(prometheus.CounterOpts{
+		Name:      "events_read_total",
+		Help:      "Total number of events read from the source.",
+		Namespace: metricNamespace,
+	})
+
 	//nolint:gochecknoglobals
 	eventsAppliedTotal = prometheus.NewCounter(prometheus.CounterOpts{
 		Name:      "events_applied_total",
@@ -144,6 +151,11 @@ func SetCopyInsertBatchDurationSeconds(dur time.Duration) {
 	copyInsertBatchDurationSeconds.Set(float64(dur.Seconds()))
 }
 
+// IncEventsRead increments the total number of events read counter.
+func IncEventsRead() {
+	eventsReadTotal.Inc()
+}
+
 // AddEventsApplied increments the total number of events applied counter.
 func AddEventsApplied(v int) {
 	eventsAppliedTotal.Add(float64(v))

pcsm/repl.go

@@ -488,6 +488,7 @@ func (r *Repl) run(opts *options.ChangeStreamOptionsBuilder) {
 		}
 
 		r.eventsRead.Add(1)
+		metrics.IncEventsRead()
 
 		if change.Namespace.Database == config.PCSMDatabase {
 			if r.bulkWrite.Empty() {