app/vmselect: add /api/v1/status/tsdb page with useful stats for locating root cause for high cardinality issues

See https://prometheus.io/docs/prometheus/latest/querying/api/#tsdb-stats

Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/425
Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/268

README.md

@@ -497,6 +497,7 @@ VictoriaMetrics supports the following handlers from [Prometheus querying API](h
 * [/api/v1/series](https://prometheus.io/docs/prometheus/latest/querying/api/#finding-series-by-label-matchers)
 * [/api/v1/labels](https://prometheus.io/docs/prometheus/latest/querying/api/#getting-label-names)
 * [/api/v1/label/.../values](https://prometheus.io/docs/prometheus/latest/querying/api/#querying-label-values)
+* [/api/v1/status/tsdb](https://prometheus.io/docs/prometheus/latest/querying/api/#tsdb-stats)
 
 These handlers can be queried from Prometheus-compatible clients such as Grafana or curl.
 
@@ -926,6 +927,12 @@ The most interesting metrics are:
   If the gaps are related to irregular intervals between samples, then try adjusting `-search.minStalenessInterval` command-line flag
   to value close to the maximum interval between samples.
 
+* Metrics and labels leading to high cardinality or high churn rate can be determined at `/api/v1/status/tsdb` page.
+  See [these docs](https://prometheus.io/docs/prometheus/latest/querying/api/#tsdb-stats) for details.
+  VictoriaMetrics accepts optional `date=YYYY-MM-DD` and `topN=42` args on this page. By default `date` equals to the current date,
+  while `topN` equals to 10.
+
+
 ### Backfilling
 
 VictoriaMetrics accepts historical data in arbitrary order of time via [any supported ingestion method](#how-to-import-time-series-data).

app/vmselect/main.go

@@ -179,6 +179,14 @@ func RequestHandler(w http.ResponseWriter, r *http.Request) bool {
 			return true
 		}
 		return true
+	case "/api/v1/status/tsdb":
+		tsdbStatusRequests.Inc()
+		if err := prometheus.TSDBStatusHandler(startTime, w, r); err != nil {
+			tsdbStatusErrors.Inc()
+			sendPrometheusError(w, r, err)
+			return true
+		}
+		return true
 	case "/api/v1/export":
 		exportRequests.Inc()
 		if err := prometheus.ExportHandler(startTime, w, r); err != nil {
@@ -191,7 +199,7 @@ func RequestHandler(w http.ResponseWriter, r *http.Request) bool {
 		federateRequests.Inc()
 		if err := prometheus.FederateHandler(startTime, w, r); err != nil {
 			federateErrors.Inc()
-			httpserver.Errorf(w, "error int %q: %s", r.URL.Path, err)
+			httpserver.Errorf(w, "error in %q: %s", r.URL.Path, err)
 			return true
 		}
 		return true
@@ -266,6 +274,9 @@ var (
 	labelsCountRequests = metrics.NewCounter(`vm_http_requests_total{path="/api/v1/labels/count"}`)
 	labelsCountErrors   = metrics.NewCounter(`vm_http_request_errors_total{path="/api/v1/labels/count"}`)
 
+	tsdbStatusRequests = metrics.NewCounter(`vm_http_requests_total{path="/api/v1/status/tsdb"}`)
+	tsdbStatusErrors   = metrics.NewCounter(`vm_http_request_errors_total{path="/api/v1/status/tsdb"}`)
+
 	deleteRequests = metrics.NewCounter(`vm_http_requests_total{path="/api/v1/admin/tsdb/delete_series"}`)
 	deleteErrors   = metrics.NewCounter(`vm_http_request_errors_total{path="/api/v1/admin/tsdb/delete_series"}`)
 

app/vmselect/netstorage/netstorage.go

@@ -449,6 +449,15 @@ func GetLabelEntries(deadline Deadline) ([]storage.TagEntry, error) {
 	return labelEntries, nil
 }
 
+// GetTSDBStatusForDate returns tsdb status according to https://prometheus.io/docs/prometheus/latest/querying/api/#tsdb-stats
+func GetTSDBStatusForDate(deadline Deadline, date uint64, topN int) (*storage.TSDBStatus, error) {
+	status, err := vmstorage.GetTSDBStatusForDate(date, topN)
+	if err != nil {
+		return nil, fmt.Errorf("error during tsdb status request: %s", err)
+	}
+	return status, nil
+}
+
 // GetSeriesCount returns the number of unique series.
 func GetSeriesCount(deadline Deadline) (uint64, error) {
 	n, err := vmstorage.GetSeriesCount()

app/vmselect/prometheus/prometheus.go

@@ -377,7 +377,6 @@ func LabelsCountHandler(startTime time.Time, w http.ResponseWriter, r *http.Requ
 	if err != nil {
 		return fmt.Errorf(`cannot obtain label entries: %s`, err)
 	}
-
 	w.Header().Set("Content-Type", "application/json")
 	WriteLabelsCountResponse(w, labelEntries)
 	labelsCountDuration.UpdateDuration(startTime)
@@ -386,6 +385,52 @@ func LabelsCountHandler(startTime time.Time, w http.ResponseWriter, r *http.Requ
 
 var labelsCountDuration = metrics.NewSummary(`vm_request_duration_seconds{path="/api/v1/labels/count"}`)
 
+const secsPerDay = 3600 * 24
+
+// TSDBStatusHandler processes /api/v1/status/tsdb request.
+//
+// See https://prometheus.io/docs/prometheus/latest/querying/api/#tsdb-stats
+func TSDBStatusHandler(startTime time.Time, w http.ResponseWriter, r *http.Request) error {
+	deadline := getDeadlineForQuery(r)
+	if err := r.ParseForm(); err != nil {
+		return fmt.Errorf("cannot parse form values: %s", err)
+	}
+	date := time.Now().Unix() / secsPerDay
+	dateStr := r.FormValue("date")
+	if len(dateStr) > 0 {
+		t, err := time.Parse("2006-01-02", dateStr)
+		if err != nil {
+			return fmt.Errorf("cannot parse `date` arg %q: %s", dateStr, err)
+		}
+		date = t.Unix() / secsPerDay
+	}
+	topN := 10
+	topNStr := r.FormValue("topN")
+	if len(topNStr) > 0 {
+		n, err := strconv.Atoi(topNStr)
+		if err != nil {
+			return fmt.Errorf("cannot parse `topN` arg %q: %s", topNStr, err)
+		}
+		if n <= 0 {
+			n = 1
+		}
+		if n > 1000 {
+			n = 1000
+		}
+		topN = n
+	}
+	status, err := netstorage.GetTSDBStatusForDate(deadline, uint64(date), topN)
+	if err != nil {
+		return fmt.Errorf(`cannot obtain tsdb status for date=%d, topN=%d: %s`, date, topN, err)
+	}
+	w.Header().Set("Content-Type", "application/json")
+	WriteTSDBStatusResponse(w, status)
+	tsdbStatusDuration.UpdateDuration(startTime)
+	return nil
+}
+
+var tsdbStatusDuration = metrics.NewSummary(`vm_request_duration_seconds{path="/api/v1/status/tsdb"}`)
+
 // LabelsHandler processes /api/v1/labels request.
 //
 // See https://prometheus.io/docs/prometheus/latest/querying/api/#getting-label-names

app/vmselect/prometheus/tsdb_status_response.qtpl

@@ -0,0 +1,28 @@
+{% import "github.com/VictoriaMetrics/VictoriaMetrics/lib/storage" %}
+
+{% stripspace %}
+TSDBStatusResponse generates response for /api/v1/status/tsdb .
+{% func TSDBStatusResponse(status *storage.TSDBStatus) %}
+{
+	"status":"success",
+	"data":{
+		"seriesCountByMetricName":{%= tsdbStatusEntries(status.SeriesCountByMetricName) %},
+		"labelValueCountByLabelName":{%= tsdbStatusEntries(status.LabelValueCountByLabelName) %},
+		"seriesCountByLabelValuePair":{%= tsdbStatusEntries(status.SeriesCountByLabelValuePair) %}
+	}
+}
+{% endfunc %}
+
+{% func tsdbStatusEntries(a []storage.TopHeapEntry) %}
+[
+	{% for i, e := range a %}
+		{
+			"name":{%q= e.Name %},
+			"value":{%d= int(e.Count) %}
+		}
+		{% if i+1 < len(a) %},{% endif %}
+	{% endfor %}
+]
+{% endfunc %}
+
+{% endstripspace %}

app/vmselect/prometheus/tsdb_status_response.qtpl.go

@@ -0,0 +1,123 @@
+// Code generated by qtc from "tsdb_status_response.qtpl". DO NOT EDIT.
+// See https://github.com/valyala/quicktemplate for details.
+
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:1
+package prometheus
+
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:1
+import "github.com/VictoriaMetrics/VictoriaMetrics/lib/storage"
+
+// TSDBStatusResponse generates response for /api/v1/status/tsdb .
+
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:5
+import (
+	qtio422016 "io"
+
+	qt422016 "github.com/valyala/quicktemplate"
+)
+
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:5
+var (
+	_ = qtio422016.Copy
+	_ = qt422016.AcquireByteBuffer
+)
+
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:5
+func StreamTSDBStatusResponse(qw422016 *qt422016.Writer, status *storage.TSDBStatus) {
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:5
+	qw422016.N().S(`{"status":"success","data":{"seriesCountByMetricName":`)
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:9
+	streamtsdbStatusEntries(qw422016, status.SeriesCountByMetricName)
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:9
+	qw422016.N().S(`,"labelValueCountByLabelName":`)
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:10
+	streamtsdbStatusEntries(qw422016, status.LabelValueCountByLabelName)
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:10
+	qw422016.N().S(`,"seriesCountByLabelValuePair":`)
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:11
+	streamtsdbStatusEntries(qw422016, status.SeriesCountByLabelValuePair)
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:11
+	qw422016.N().S(`}}`)
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:14
+}
+
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:14
+func WriteTSDBStatusResponse(qq422016 qtio422016.Writer, status *storage.TSDBStatus) {
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:14
+	qw422016 := qt422016.AcquireWriter(qq422016)
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:14
+	StreamTSDBStatusResponse(qw422016, status)
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:14
+	qt422016.ReleaseWriter(qw422016)
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:14
+}
+
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:14
+func TSDBStatusResponse(status *storage.TSDBStatus) string {
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:14
+	qb422016 := qt422016.AcquireByteBuffer()
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:14
+	WriteTSDBStatusResponse(qb422016, status)
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:14
+	qs422016 := string(qb422016.B)
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:14
+	qt422016.ReleaseByteBuffer(qb422016)
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:14
+	return qs422016
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:14
+}
+
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:16
+func streamtsdbStatusEntries(qw422016 *qt422016.Writer, a []storage.TopHeapEntry) {
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:16
+	qw422016.N().S(`[`)
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:18
+	for i, e := range a {
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:18
+		qw422016.N().S(`{"name":`)
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:20
+		qw422016.N().Q(e.Name)
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:20
+		qw422016.N().S(`,"value":`)
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:21
+		qw422016.N().D(int(e.Count))
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:21
+		qw422016.N().S(`}`)
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:23
+		if i+1 < len(a) {
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:23
+			qw422016.N().S(`,`)
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:23
+		}
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:24
+	}
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:24
+	qw422016.N().S(`]`)
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:26
+}
+
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:26
+func writetsdbStatusEntries(qq422016 qtio422016.Writer, a []storage.TopHeapEntry) {
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:26
+	qw422016 := qt422016.AcquireWriter(qq422016)
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:26
+	streamtsdbStatusEntries(qw422016, a)
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:26
+	qt422016.ReleaseWriter(qw422016)
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:26
+}
+
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:26
+func tsdbStatusEntries(a []storage.TopHeapEntry) string {
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:26
+	qb422016 := qt422016.AcquireByteBuffer()
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:26
+	writetsdbStatusEntries(qb422016, a)
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:26
+	qs422016 := string(qb422016.B)
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:26
+	qt422016.ReleaseByteBuffer(qb422016)
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:26
+	return qs422016
+//line app/vmselect/prometheus/tsdb_status_response.qtpl:26
+}

app/vmstorage/main.go

@@ -120,6 +120,14 @@ func SearchTagEntries(maxTagKeys, maxTagValues int) ([]storage.TagEntry, error)
 	return tagEntries, err
 }
 
+// GetTSDBStatusForDate returns TSDB status for the given date.
+func GetTSDBStatusForDate(date uint64, topN int) (*storage.TSDBStatus, error) {
+	WG.Add(1)
+	status, err := Storage.GetTSDBStatusForDate(date, topN)
+	WG.Done()
+	return status, err
+}
+
 // GetSeriesCount returns the number of time series in the storage.
 func GetSeriesCount() (uint64, error) {
 	WG.Add(1)

docs/Single-server-VictoriaMetrics.md

@@ -497,6 +497,7 @@ VictoriaMetrics supports the following handlers from [Prometheus querying API](h
 * [/api/v1/series](https://prometheus.io/docs/prometheus/latest/querying/api/#finding-series-by-label-matchers)
 * [/api/v1/labels](https://prometheus.io/docs/prometheus/latest/querying/api/#getting-label-names)
 * [/api/v1/label/.../values](https://prometheus.io/docs/prometheus/latest/querying/api/#querying-label-values)
+* [/api/v1/status/tsdb](https://prometheus.io/docs/prometheus/latest/querying/api/#tsdb-stats)
 
 These handlers can be queried from Prometheus-compatible clients such as Grafana or curl.
 
@@ -926,6 +927,12 @@ The most interesting metrics are:
   If the gaps are related to irregular intervals between samples, then try adjusting `-search.minStalenessInterval` command-line flag
   to value close to the maximum interval between samples.
 
+* Metrics and labels leading to high cardinality or high churn rate can be determined at `/api/v1/status/tsdb` page.
+  See [these docs](https://prometheus.io/docs/prometheus/latest/querying/api/#tsdb-stats) for details.
+  VictoriaMetrics accepts optional `date=YYYY-MM-DD` and `topN=42` args on this page. By default `date` equals to the current date,
+  while `topN` equals to 10.
+
+
 ### Backfilling
 
 VictoriaMetrics accepts historical data in arbitrary order of time via [any supported ingestion method](#how-to-import-time-series-data).

lib/storage/index_db.go

@@ -2,6 +2,7 @@ package storage
 
 import (
 	"bytes"
+	"container/heap"
 	"errors"
 	"fmt"
 	"io"
@@ -882,11 +883,232 @@ func (db *indexDB) GetSeriesCount() (uint64, error) {
 		extDB.putIndexSearch(is)
 	})
 	if ok && err != nil {
-		return 0, err
+		return 0, fmt.Errorf("error when searching in extDB: %s", err)
 	}
 	return n + nExt, nil
 }
 
+func (is *indexSearch) getSeriesCount() (uint64, error) {
+	ts := &is.ts
+	kb := &is.kb
+	mp := &is.mp
+	var metricIDsLen uint64
+	// Extract the number of series from ((__name__=value): metricIDs) rows
+	kb.B = marshalCommonPrefix(kb.B[:0], nsPrefixTagToMetricIDs)
+	kb.B = marshalTagValue(kb.B, nil)
+	ts.Seek(kb.B)
+	for ts.NextItem() {
+		item := ts.Item
+		if !bytes.HasPrefix(item, kb.B) {
+			break
+		}
+		tail := item[len(kb.B):]
+		n := bytes.IndexByte(tail, tagSeparatorChar)
+		if n < 0 {
+			return 0, fmt.Errorf("invalid tag->metricIDs line %q: cannot find tagSeparatorChar %d", item, tagSeparatorChar)
+		}
+		tail = tail[n+1:]
+		if err := mp.InitOnlyTail(item, tail); err != nil {
+			return 0, err
+		}
+		// Take into account deleted timeseries too.
+		// It is OK if series can be counted multiple times in rare cases -
+		// the returned number is an estimation.
+		metricIDsLen += uint64(mp.MetricIDsLen())
+	}
+	if err := ts.Error(); err != nil {
+		return 0, fmt.Errorf("error when counting unique timeseries: %s", err)
+	}
+	return metricIDsLen, nil
+}
+
+// GetTSDBStatusForDate returns topN entries for tsdb status for the given date.
+func (db *indexDB) GetTSDBStatusForDate(date uint64, topN int) (*TSDBStatus, error) {
+	is := db.getIndexSearch()
+	status, err := is.getTSDBStatusForDate(date, topN)
+	db.putIndexSearch(is)
+	if err != nil {
+		return nil, err
+	}
+	if status.hasEntries() {
+		// The entries were found in the db. There is no need in searching them in extDB.
+		return status, nil
+	}
+
+	// The entries weren't found in the db. Try searching them in extDB.
+	ok := db.doExtDB(func(extDB *indexDB) {
+		is := extDB.getIndexSearch()
+		status, err = is.getTSDBStatusForDate(date, topN)
+		extDB.putIndexSearch(is)
+	})
+	if ok && err != nil {
+		return nil, fmt.Errorf("error when obtaining TSDB status from extDB: %s", err)
+	}
+	return status, nil
+}
+
+func (is *indexSearch) getTSDBStatusForDate(date uint64, topN int) (*TSDBStatus, error) {
+	ts := &is.ts
+	kb := &is.kb
+	mp := &is.mp
+	thLabelValueCountByLabelName := newTopHeap(topN)
+	thSeriesCountByLabelValuePair := newTopHeap(topN)
+	thSeriesCountByMetricName := newTopHeap(topN)
+	var tmp, labelName, labelNameValue []byte
+	var labelValueCountByLabelName, seriesCountByLabelValuePair uint64
+	nameEqualBytes := []byte("__name__=")
+
+	kb.B = marshalCommonPrefix(kb.B[:0], nsPrefixDateTagToMetricIDs)
+	kb.B = encoding.MarshalUint64(kb.B, date)
+	prefix := kb.B
+	ts.Seek(prefix)
+	for ts.NextItem() {
+		item := ts.Item
+		if !bytes.HasPrefix(item, prefix) {
+			break
+		}
+		tail := item[len(prefix):]
+		var err error
+		tail, tmp, err = unmarshalTagValue(tmp[:0], tail)
+		if err != nil {
+			return nil, fmt.Errorf("cannot unmarshal tag key from line %q: %s", item, err)
+		}
+		if len(tmp) == 0 {
+			tmp = append(tmp, "__name__"...)
+		}
+		if !bytes.Equal(tmp, labelName) {
+			thLabelValueCountByLabelName.pushIfNonEmpty(labelName, labelValueCountByLabelName)
+			labelValueCountByLabelName = 0
+			labelName = append(labelName[:0], tmp...)
+		}
+		tmp = append(tmp, '=')
+		tail, tmp, err = unmarshalTagValue(tmp, tail)
+		if err != nil {
+			return nil, fmt.Errorf("cannot unmarshal tag value from line %q: %s", item, err)
+		}
+		if !bytes.Equal(tmp, labelNameValue) {
+			thSeriesCountByLabelValuePair.pushIfNonEmpty(labelNameValue, seriesCountByLabelValuePair)
+			if bytes.HasPrefix(labelNameValue, nameEqualBytes) {
+				thSeriesCountByMetricName.pushIfNonEmpty(labelNameValue[len(nameEqualBytes):], seriesCountByLabelValuePair)
+			}
+			seriesCountByLabelValuePair = 0
+			labelValueCountByLabelName++
+			labelNameValue = append(labelNameValue[:0], tmp...)
+		}
+		if err := mp.InitOnlyTail(item, tail); err != nil {
+			return nil, err
+		}
+		// Take into account deleted timeseries too.
+		// It is OK if series can be counted multiple times in rare cases -
+		// the returned number is an estimation.
+		seriesCountByLabelValuePair += uint64(mp.MetricIDsLen())
+	}
+	if err := ts.Error(); err != nil {
+		return nil, fmt.Errorf("error when counting time series by metric names: %s", err)
+	}
+	thLabelValueCountByLabelName.pushIfNonEmpty(labelName, labelValueCountByLabelName)
+	thSeriesCountByLabelValuePair.pushIfNonEmpty(labelNameValue, seriesCountByLabelValuePair)
+	if bytes.HasPrefix(labelNameValue, nameEqualBytes) {
+		thSeriesCountByMetricName.pushIfNonEmpty(labelNameValue[len(nameEqualBytes):], seriesCountByLabelValuePair)
+	}
+	status := &TSDBStatus{
+		SeriesCountByMetricName:     thSeriesCountByMetricName.getSortedResult(),
+		LabelValueCountByLabelName:  thLabelValueCountByLabelName.getSortedResult(),
+		SeriesCountByLabelValuePair: thSeriesCountByLabelValuePair.getSortedResult(),
+	}
+	return status, nil
+}
+
+// TSDBStatus contains TSDB status data for /api/v1/status/tsdb.
+//
+// See https://prometheus.io/docs/prometheus/latest/querying/api/#tsdb-stats
+type TSDBStatus struct {
+	SeriesCountByMetricName     []TopHeapEntry
+	LabelValueCountByLabelName  []TopHeapEntry
+	SeriesCountByLabelValuePair []TopHeapEntry
+}
+
+func (status *TSDBStatus) hasEntries() bool {
+	return len(status.SeriesCountByLabelValuePair) > 0
+}
+
+// topHeap maintains a heap of topHeapEntries with the maximum TopHeapEntry.n values.
+type topHeap struct {
+	topN int
+	a    []TopHeapEntry
+}
+
+// newTopHeap returns topHeap for topN items.
+func newTopHeap(topN int) *topHeap {
+	return &topHeap{
+		topN: topN,
+	}
+}
+
+// TopHeapEntry represents an entry from `top heap` used in stats.
+type TopHeapEntry struct {
+	Name  string
+	Count uint64
+}
+
+func (th *topHeap) pushIfNonEmpty(name []byte, count uint64) {
+	if count == 0 {
+		return
+	}
+	if len(th.a) < th.topN {
+		th.a = append(th.a, TopHeapEntry{
+			Name:  string(name),
+			Count: count,
+		})
+		heap.Fix(th, len(th.a)-1)
+		return
+	}
+	if count <= th.a[0].Count {
+		return
+	}
+	th.a[0] = TopHeapEntry{
+		Name:  string(name),
+		Count: count,
+	}
+	heap.Fix(th, 0)
+}
+
+func (th *topHeap) getSortedResult() []TopHeapEntry {
+	result := append([]TopHeapEntry{}, th.a...)
+	sort.Slice(result, func(i, j int) bool {
+		a, b := result[i], result[j]
+		if a.Count != b.Count {
+			return a.Count > b.Count
+		}
+		return a.Name < b.Name
+	})
+	return result
+}
+
+// heap.Interface implementation for topHeap.
+
+func (th *topHeap) Len() int {
+	return len(th.a)
+}
+
+func (th *topHeap) Less(i, j int) bool {
+	a := th.a
+	return a[i].Count < a[j].Count
+}
+
+func (th *topHeap) Swap(i, j int) {
+	a := th.a
+	a[j], a[i] = a[i], a[j]
+}
+
+func (th *topHeap) Push(x interface{}) {
+	panic(fmt.Errorf("BUG: Push shouldn't be called"))
+}
+
+func (th *topHeap) Pop() interface{} {
+	panic(fmt.Errorf("BUG: Pop shouldn't be called"))
+}
+
 // searchMetricName appends metric name for the given metricID to dst
 // and returns the result.
 func (db *indexDB) searchMetricName(dst []byte, metricID uint64) ([]byte, error) {
@@ -1314,40 +1536,6 @@ func (is *indexSearch) getTSIDByMetricID(dst *TSID, metricID uint64) error {
 	return nil
 }
 
-func (is *indexSearch) getSeriesCount() (uint64, error) {
-	ts := &is.ts
-	kb := &is.kb
-	mp := &is.mp
-	var metricIDsLen uint64
-	// Extract the number of series from ((__name__=value): metricIDs) rows
-	kb.B = marshalCommonPrefix(kb.B[:0], nsPrefixTagToMetricIDs)
-	kb.B = marshalTagValue(kb.B, nil)
-	ts.Seek(kb.B)
-	for ts.NextItem() {
-		item := ts.Item
-		if !bytes.HasPrefix(item, kb.B) {
-			break
-		}
-		tail := item[len(kb.B):]
-		n := bytes.IndexByte(tail, tagSeparatorChar)
-		if n < 0 {
-			return 0, fmt.Errorf("invalid tag->metricIDs line %q: cannot find tagSeparatorChar %d", item, tagSeparatorChar)
-		}
-		tail = tail[n+1:]
-		if err := mp.InitOnlyTail(item, tail); err != nil {
-			return 0, err
-		}
-		// Take into account deleted timeseries too.
-		// It is OK if series can be counted multiple times in rare cases -
-		// the returned number is an estimation.
-		metricIDsLen += uint64(mp.MetricIDsLen())
-	}
-	if err := ts.Error(); err != nil {
-		return 0, fmt.Errorf("error when counting unique timeseries: %s", err)
-	}
-	return metricIDsLen, nil
-}
-
 // updateMetricIDsByMetricNameMatch matches metricName values for the given srcMetricIDs against tfs
 // and adds matching metrics to metricIDs.
 func (is *indexSearch) updateMetricIDsByMetricNameMatch(metricIDs, srcMetricIDs *uint64set.Set, tfs []*tagFilter) error {

lib/storage/index_db_test.go

@@ -1540,6 +1540,70 @@ func TestSearchTSIDWithTimeRange(t *testing.T) {
 	if len(matchedTSIDs) != metricsPerDay*days {
 		t.Fatal("Expected time series for all days, got", len(matchedTSIDs))
 	}
+
+	// Check GetTSDBStatusForDate
+	status, err := db.GetTSDBStatusForDate(baseDate, 5)
+	if err != nil {
+		t.Fatalf("error in GetTSDBStatusForDate: %s", err)
+	}
+	if !status.hasEntries() {
+		t.Fatalf("expecting non-empty TSDB status")
+	}
+	expectedSeriesCountByMetricName := []TopHeapEntry{
+		{
+			Name:  "testMetric",
+			Count: 1000,
+		},
+	}
+	if !reflect.DeepEqual(status.SeriesCountByMetricName, expectedSeriesCountByMetricName) {
+		t.Fatalf("unexpected SeriesCountByMetricName;\ngot\n%v\nwant\n%v", status.SeriesCountByMetricName, expectedSeriesCountByMetricName)
+	}
+	expectedLabelValueCountByLabelName := []TopHeapEntry{
+		{
+			Name:  "uniqueid",
+			Count: 1000,
+		},
+		{
+			Name:  "__name__",
+			Count: 1,
+		},
+		{
+			Name:  "constant",
+			Count: 1,
+		},
+		{
+			Name:  "day",
+			Count: 1,
+		},
+	}
+	if !reflect.DeepEqual(status.LabelValueCountByLabelName, expectedLabelValueCountByLabelName) {
+		t.Fatalf("unexpected LabelValueCountByLabelName;\ngot\n%v\nwant\n%v", status.LabelValueCountByLabelName, expectedLabelValueCountByLabelName)
+	}
+	expectedSeriesCountByLabelValuePair := []TopHeapEntry{
+		{
+			Name:  "__name__=testMetric",
+			Count: 1000,
+		},
+		{
+			Name:  "constant=const",
+			Count: 1000,
+		},
+		{
+			Name:  "day=0",
+			Count: 1000,
+		},
+		{
+			Name:  "uniqueid=0",
+			Count: 1,
+		},
+		{
+			Name:  "uniqueid=1",
+			Count: 1,
+		},
+	}
+	if !reflect.DeepEqual(status.SeriesCountByLabelValuePair, expectedSeriesCountByLabelValuePair) {
+		t.Fatalf("unexpected SeriesCountByLabelValuePair;\ngot\n%v\nwant\n%v", status.SeriesCountByLabelValuePair, expectedSeriesCountByLabelValuePair)
+	}
 }
 
 func toTFPointers(tfs []tagFilter) []*tagFilter {

lib/storage/storage.go

@@ -780,6 +780,13 @@ func (s *Storage) GetSeriesCount() (uint64, error) {
 	return s.idb().GetSeriesCount()
 }
 
+// GetTSDBStatusForDate returns TSDB status data for /api/v1/status/tsdb.
+//
+// See https://prometheus.io/docs/prometheus/latest/querying/api/#tsdb-stats
+func (s *Storage) GetTSDBStatusForDate(date uint64, topN int) (*TSDBStatus, error) {
+	return s.idb().GetTSDBStatusForDate(date, topN)
+}
+
 // MetricRow is a metric to insert into storage.
 type MetricRow struct {
 	// MetricNameRaw contains raw metric name, which must be decoded