ingester: Add `ingester_memory_streams_labels_bytes` metric (#8212)

Signed-off-by: Kaviraj <kavirajkanagaraj@gmail.com>

This is to give visibility on `labels` size of in-memory streams on the
ingesters.

It caculate the size of labels via `len(labels.String())`. Meaning if
you have
```go
	lbs := labels.Labels{
		{Name: "foo", Value: "bar"},
		{Name: "instance", Value: "loki"},
	}
```
size would be number of bytes in `{foo="bar", instance="loki"}` which is
`28`. NOTE: `len(string)` gives [bytes length in
Go](https://pkg.go.dev/builtin#len)

CHANGELOG.md

@@ -26,6 +26,7 @@
 * [8047](https://github.com/grafana/loki/pull/8047) **bboreham**: Dashboards: add k8s resource requests to CPU and memory panels.
 * [8061](https://github.com/grafana/loki/pull/8061) **kavirajk**: Remove circle from Loki OSS
 * [8131](https://github.com/grafana/loki/pull/8131) **jeschkies**: Compile Promtail ARM and ARM64 with journald support.
+* [8212](https://github.com/grafana/loki/pull/8212) **kavirajk**: ingester: Add `ingester_memory_streams_labels_bytes metric` for more visibility of size of metadata of in-memory streams.
 
 ##### Fixes
 

pkg/ingester/instance.go

@@ -53,6 +53,11 @@ var (
 		Name:      "ingester_memory_streams",
 		Help:      "The total number of streams in memory per tenant.",
 	}, []string{"tenant"})
+	memoryStreamsLabelsBytes = promauto.NewGauge(prometheus.GaugeOpts{
+		Namespace: "loki",
+		Name:      "ingester_memory_streams_labels_bytes",
+		Help:      "Total bytes of labels of the streams in memory.",
+	})
 	streamsCreatedTotal = promauto.NewCounterVec(prometheus.CounterOpts{
 		Namespace: "loki",
 		Name:      "ingester_streams_created_total",
@@ -279,6 +284,7 @@ func (i *instance) createStream(pushReqStream logproto.Stream, record *WALRecord
 	}
 
 	memoryStreams.WithLabelValues(i.instanceID).Inc()
+	memoryStreamsLabelsBytes.Add(float64(len(s.labels.String())))
 	i.streamsCreatedTotal.Inc()
 	i.addTailersToNewStream(s)
 	streamsCountStats.Add(1)
@@ -300,6 +306,7 @@ func (i *instance) createStreamByFP(ls labels.Labels, fp model.Fingerprint) *str
 
 	i.streamsCreatedTotal.Inc()
 	memoryStreams.WithLabelValues(i.instanceID).Inc()
+	memoryStreamsLabelsBytes.Add(float64(len(s.labels.String())))
 	i.addTailersToNewStream(s)
 
 	return s
@@ -322,6 +329,7 @@ func (i *instance) removeStream(s *stream) {
 		i.index.Delete(s.labels, s.fp)
 		i.streamsRemovedTotal.Inc()
 		memoryStreams.WithLabelValues(i.instanceID).Dec()
+		memoryStreamsLabelsBytes.Sub(float64(len(s.labels.String())))
 		streamsCountStats.Add(-1)
 	}
 }