NumSeries in Meta() of Head

Signed-off-by: Ganesh Vernekar <cs15btech11018@iith.ac.in>

head.go

@@ -65,6 +65,7 @@ type Head struct {
 	logger     log.Logger
 	appendPool sync.Pool
 	bytesPool  sync.Pool
+	numSeries  uint64
 
 	minTime, maxTime int64 // Current min and max of the samples included in the head.
 	minValidTime     int64 // Mint allowed to be added to the head. It shouldn't be lower than the maxt of the last persisted block.
@@ -85,7 +86,7 @@ type Head struct {
 
 type headMetrics struct {
 	activeAppenders         prometheus.Gauge
-	series                  prometheus.Gauge
+	series                  prometheus.GaugeFunc
 	seriesCreated           prometheus.Counter
 	seriesRemoved           prometheus.Counter
 	seriesNotFound          prometheus.Counter
@@ -113,9 +114,11 @@ func newHeadMetrics(h *Head, r prometheus.Registerer) *headMetrics {
 		Name: "prometheus_tsdb_head_active_appenders",
 		Help: "Number of currently active appender transactions",
 	})
-	m.series = prometheus.NewGauge(prometheus.GaugeOpts{
+	m.series = prometheus.NewGaugeFunc(prometheus.GaugeOpts{
 		Name: "prometheus_tsdb_head_series",
 		Help: "Total number of series in the head block.",
+	}, func() float64 {
+		return float64(h.NumSeries())
 	})
 	m.seriesCreated = prometheus.NewCounter(prometheus.CounterOpts{
 		Name: "prometheus_tsdb_head_series_created_total",
@@ -699,11 +702,18 @@ func (h *rangeHead) MaxTime() int64 {
 	return h.maxt
 }
 
+func (h *rangeHead) NumSeries() uint64 {
+	return h.head.NumSeries()
+}
+
 func (h *rangeHead) Meta() BlockMeta {
 	return BlockMeta{
 		MinTime: h.MinTime(),
 		MaxTime: h.MaxTime(),
 		ULID:    h.head.Meta().ULID,
+		Stats: BlockStats{
+			NumSeries: h.NumSeries(),
+		},
 	}
 }
 
@@ -1031,9 +1041,10 @@ func (h *Head) gc() {
 	seriesRemoved := len(deleted)
 
 	h.metrics.seriesRemoved.Add(float64(seriesRemoved))
-	h.metrics.series.Sub(float64(seriesRemoved))
 	h.metrics.chunksRemoved.Add(float64(chunksRemoved))
 	h.metrics.chunks.Sub(float64(chunksRemoved))
+	// Ref: https://golang.org/pkg/sync/atomic/#AddUint64
+	atomic.AddUint64(&h.numSeries, ^uint64(seriesRemoved-1))
 
 	// Remove deleted series IDs from the postings lists.
 	h.postings.Delete(deleted)
@@ -1110,6 +1121,11 @@ func (h *Head) chunksRange(mint, maxt int64) *headChunkReader {
 	return &headChunkReader{head: h, mint: mint, maxt: maxt}
 }
 
+// NumSeries returns the number of active series in the head.
+func (h *Head) NumSeries() uint64 {
+	return atomic.LoadUint64(&h.numSeries)
+}
+
 // Meta returns meta information about the head.
 func (h *Head) Meta() BlockMeta {
 	var id [16]byte
@@ -1118,6 +1134,9 @@ func (h *Head) Meta() BlockMeta {
 		MinTime: h.MinTime(),
 		MaxTime: h.MaxTime(),
 		ULID:    ulid.ULID(id),
+		Stats: BlockStats{
+			NumSeries: h.NumSeries(),
+		},
 	}
 }
 
@@ -1367,8 +1386,8 @@ func (h *Head) getOrCreateWithID(id, hash uint64, lset labels.Labels) (*memSerie
 		return s, false
 	}
 
-	h.metrics.series.Inc()
 	h.metrics.seriesCreated.Inc()
+	atomic.AddUint64(&h.numSeries, 1)
 
 	h.postings.Add(id, lset)