Add 'VStreamerCount' metric to vttablet

go/vt/vttablet/tabletserver/vstreamer/engine.go

@@ -88,6 +88,7 @@ type Engine struct {
 	rowStreamerNumRows        *stats.Counter
 	rowStreamerNumPackets     *stats.Counter
 	errorCounts               *stats.CountersWithSingleLabel
+	vstreamersActive          *stats.GaugeFunc
 	vstreamersCreated         *stats.Counter
 	vstreamersEndedWithErrors *stats.Counter
 
@@ -126,6 +127,8 @@ func NewEngine(env tabletenv.Env, ts srvtopo.Server, se *schema.Engine, lagThrot
 		vstreamersEndedWithErrors: env.Exporter().NewCounter("VStreamersEndedWithErrors", "Count of vstreamers that ended with errors"),
 		errorCounts:               env.Exporter().NewCountersWithSingleLabel("VStreamerErrors", "Tracks errors in vstreamer", "type", "Catchup", "Copy", "Send", "TablePlan"),
 	}
+	vse.vstreamersActive = env.Exporter().NewGaugeFunc("VStreamersActive", "Count of vstreamers active", vse.getStreamersActive)
+
 	env.Exporter().HandleFunc("/debug/tablet_vschema", vse.ServeHTTP)
 	return vse
 }
@@ -375,6 +378,10 @@ func (vse *Engine) setWatch() {
 	})
 }
 
+func (vse *Engine) getStreamersActive() int64 {
+	return int64(len(vse.streamers))
+}
+
 func getPacketSize() int64 {
 	return int64(*defaultPacketSize)
 }