app/vmselect/prometheus: improve performance for /api/v1/labels and /api/v1/label/<labelName>/values on time ranges exceeding one day when match[] query arg is set

app/vmselect/prometheus/prometheus.go

@@ -662,12 +662,28 @@ func labelValuesWithMatches(at *auth.Token, denyPartialResponse bool, labelName
 		MaxTimestamp: end,
 		TagFilterss:  tagFilterss,
 	}
-	rss, isPartial, err := netstorage.ProcessSearchQuery(at, denyPartialResponse, sq, false, deadline)
+	m := make(map[string]struct{})
+	isPartial := false
+	if end-start > 24*3600*1000 {
+		// It is cheaper to call SearchMetricNames on time ranges exceeding a day.
+		mns, isPartialResponse, err := netstorage.SearchMetricNames(at, denyPartialResponse, sq, deadline)
+		if err != nil {
+			return nil, false, fmt.Errorf("cannot fetch time series for %q: %w", sq, err)
+		}
+		isPartial = isPartialResponse
+		for _, mn := range mns {
+			labelValue := mn.GetTagValue(labelName)
+			if len(labelValue) == 0 {
+				continue
+			}
+			m[string(labelValue)] = struct{}{}
+		}
+	} else {
+		rss, isPartialResponse, err := netstorage.ProcessSearchQuery(at, denyPartialResponse, sq, false, deadline)
 		if err != nil {
 			return nil, false, fmt.Errorf("cannot fetch data for %q: %w", sq, err)
 		}
-
+		isPartial = isPartialResponse
-	m := make(map[string]struct{})
 		var mLock sync.Mutex
 		err = rss.RunParallel(func(rs *netstorage.Result, workerID uint) error {
 			labelValue := rs.MetricName.GetTagValue(labelName)
@@ -682,7 +698,7 @@ func labelValuesWithMatches(at *auth.Token, denyPartialResponse bool, labelName
 		if err != nil {
 			return nil, false, fmt.Errorf("error when data fetching: %w", err)
 		}
-
+	}
 	labelValues := make([]string, 0, len(m))
 	for labelValue := range m {
 		labelValues = append(labelValues, labelValue)
@@ -856,19 +872,31 @@ func labelsWithMatches(at *auth.Token, denyPartialResponse bool, matches []strin
 		MaxTimestamp: end,
 		TagFilterss:  tagFilterss,
 	}
-	rss, isPartial, err := netstorage.ProcessSearchQuery(at, denyPartialResponse, sq, false, deadline)
+	m := make(map[string]struct{})
+	isPartial := false
+	if end-start > 24*3600*1000 {
+		// It is cheaper to call SearchMetricNames on time ranges exceeding a day.
+		mns, isPartialResponse, err := netstorage.SearchMetricNames(at, denyPartialResponse, sq, deadline)
+		if err != nil {
+			return nil, false, fmt.Errorf("cannot fetch time series for %q: %w", sq, err)
+		}
+		isPartial = isPartialResponse
+		for _, mn := range mns {
+			for _, tag := range mn.Tags {
+				m[string(tag.Key)] = struct{}{}
+			}
+		}
+	} else {
+		rss, isPartialResponse, err := netstorage.ProcessSearchQuery(at, denyPartialResponse, sq, false, deadline)
 		if err != nil {
 			return nil, false, fmt.Errorf("cannot fetch data for %q: %w", sq, err)
 		}
-
+		isPartial = isPartialResponse
-	m := make(map[string]struct{})
 		var mLock sync.Mutex
 		err = rss.RunParallel(func(rs *netstorage.Result, workerID uint) error {
 			mLock.Lock()
-		tags := rs.MetricName.Tags
+			for _, tag := range rs.MetricName.Tags {
-		for i := range tags {
+				m[string(tag.Key)] = struct{}{}
-			t := &tags[i]
-			m[string(t.Key)] = struct{}{}
 			}
 			m["__name__"] = struct{}{}
 			mLock.Unlock()
@@ -877,6 +905,7 @@ func labelsWithMatches(at *auth.Token, denyPartialResponse bool, matches []strin
 		if err != nil {
 			return nil, false, fmt.Errorf("error when data fetching: %w", err)
 		}
+	}
 
 	labels := make([]string, 0, len(m))
 	for label := range m {

docs/CHANGELOG.md

@@ -7,7 +7,7 @@
 * FEATURE: vmselect: add `"isPartial":{true|false}` field in JSON output for `/api/v1/*` functions
   from [Prometheus querying API](https://prometheus.io/docs/prometheus/latest/querying/api/). `"isPartial":true` is set if the response contains partial data
   because of a part of `vmstorage` nodes were unavailable during query processing.
-* FEATURE: improve performance for `/api/v1/series` on time ranges exceeding one day.
+* FEATURE: improve performance for `/api/v1/series`, `/api/v1/labels` and `/api/v1/label/<labelName>/values` on time ranges exceeding one day.
 * FEATURE: vmagent: reduce memory usage when service discovery detects big number of scrape targets and the set of discovered targets changes over time.
   See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/825
 * FEATURE: vmagent: add `-promscrape.dropOriginalLabels` command-line option, which can be used for reducing memory usage when scraping big number of targets.