store: label_values: fetch less postings

CHANGELOG.md

@@ -19,6 +19,7 @@ We use *breaking :warning:* to mark changes that are not backward compatible (re
 - [#7658](https://github.com/thanos-io/thanos/pull/7658) Store: Fix panic because too small buffer in pool.
 - [#7643](https://github.com/thanos-io/thanos/pull/7643) Receive: fix thanos_receive_write_{timeseries,samples} stats
 - [#7644](https://github.com/thanos-io/thanos/pull/7644) fix(ui): add null check to find overlapping blocks logic
+- [#7814](https://github.com/thanos-io/thanos/pull/7814) Store: label_values: fetch less postings.
 - [#7679](https://github.com/thanos-io/thanos/pull/7679) Query: respect store.limit.* flags when evaluating queries
 
 ### Added

pkg/store/acceptance_test.go

@@ -740,6 +740,46 @@ func testStoreAPIsAcceptance(t *testing.T, startStore startStoreFn) {
 				},
 			},
 		},
+		{
+			desc: "label_values(kube_pod_info{}, pod) don't fetch postings for pod!=''",
+			appendFn: func(app storage.Appender) {
+				_, err := app.Append(0, labels.FromStrings("__name__", "up", "pod", "pod-1"), timestamp.FromTime(now), 1)
+				testutil.Ok(t, err)
+				_, err = app.Append(0, labels.FromStrings("__name__", "up", "pod", "pod-2"), timestamp.FromTime(now), 1)
+				testutil.Ok(t, err)
+				_, err = app.Append(0, labels.FromStrings("__name__", "kube_pod_info", "pod", "pod-1"), timestamp.FromTime(now), 1)
+				testutil.Ok(t, err)
+				testutil.Ok(t, app.Commit())
+			},
+			labelNameCalls: []labelNameCallCase{
+				{
+					start:         timestamp.FromTime(minTime),
+					end:           timestamp.FromTime(maxTime),
+					expectedNames: []string{"__name__", "pod", "region"},
+					matchers:      []storepb.LabelMatcher{{Type: storepb.LabelMatcher_EQ, Name: "__name__", Value: "kube_pod_info"}},
+				},
+				{
+					start:         timestamp.FromTime(minTime),
+					end:           timestamp.FromTime(maxTime),
+					expectedNames: []string{"__name__", "pod", "region"},
+				},
+			},
+			labelValuesCalls: []labelValuesCallCase{
+				{
+					start:          timestamp.FromTime(minTime),
+					end:            timestamp.FromTime(maxTime),
+					label:          "pod",
+					expectedValues: []string{"pod-1"},
+					matchers:       []storepb.LabelMatcher{{Type: storepb.LabelMatcher_EQ, Name: "__name__", Value: "kube_pod_info"}},
+				},
+				{
+					start:          timestamp.FromTime(minTime),
+					end:            timestamp.FromTime(maxTime),
+					label:          "pod",
+					expectedValues: []string{"pod-1", "pod-2"},
+				},
+			},
+		},
 	} {
 		t.Run(tc.desc, func(t *testing.T) {
 			appendFn := tc.appendFn

pkg/store/bucket.go

@@ -1992,6 +1992,14 @@ func (s *BucketStore) LabelValues(ctx context.Context, req *storepb.LabelValuesR
 
 	resHints := &hintspb.LabelValuesResponseHints{}
 
+	var hasMetricNameEqMatcher = false
+	for _, m := range reqSeriesMatchers {
+		if m.Name == labels.MetricName && m.Type == labels.MatchEqual {
+			hasMetricNameEqMatcher = true
+			break
+		}
+	}
+
 	g, gctx := errgroup.WithContext(ctx)
 
 	var reqBlockMatchers []*labels.Matcher
@@ -2015,6 +2023,7 @@ func (s *BucketStore) LabelValues(ctx context.Context, req *storepb.LabelValuesR
 	var seriesLimiter = s.seriesLimiterFactory(s.metrics.queriesDropped.WithLabelValues("series", tenant))
 	var bytesLimiter = s.bytesLimiterFactory(s.metrics.queriesDropped.WithLabelValues("bytes", tenant))
 	var logger = s.requestLoggerFunc(ctx, s.logger)
+	var stats = &queryStats{}
 
 	for _, b := range s.blocks {
 		b := b
@@ -2033,7 +2042,8 @@ func (s *BucketStore) LabelValues(ctx context.Context, req *storepb.LabelValuesR
 
 		// If we have series matchers and the Label is not an external one, add <labelName> != "" matcher
 		// to only select series that have given label name.
-		if len(reqSeriesMatchersNoExtLabels) > 0 && !b.extLset.Has(req.Label) {
+		// We don't need such matcher if matchers already contain __name__=="something" matcher.
+		if !hasMetricNameEqMatcher && len(reqSeriesMatchersNoExtLabels) > 0 && !b.extLset.Has(req.Label) {
 			m, err := labels.NewMatcher(labels.MatchNotEqual, req.Label, "")
 			if err != nil {
 				return nil, status.Error(codes.InvalidArgument, err.Error())
@@ -2101,7 +2111,12 @@ func (s *BucketStore) LabelValues(ctx context.Context, req *storepb.LabelValuesR
 					s.metrics.lazyExpandedPostingSeriesOverfetchedSizeBytes,
 					tenant,
 				)
-				defer blockClient.Close()
+				defer func() {
+					mtx.Lock()
+					stats = blockClient.MergeStats(stats)
+					mtx.Unlock()
+					blockClient.Close()
+				}()
 
 				if err := blockClient.ExpandPostings(
 					sortedReqSeriesMatchersNoExtLabels,
@@ -2130,7 +2145,7 @@ func (s *BucketStore) LabelValues(ctx context.Context, req *storepb.LabelValuesR
 					}
 
 					val := labelpb.ZLabelsToPromLabels(ls.GetSeries().Labels).Get(req.Label)
-					if val != "" { // Should never be empty since we added labelName!="" matcher to the list of matchers.
+					if val != "" {
 						values[val] = struct{}{}
 					}
 				}
@@ -2154,6 +2169,15 @@ func (s *BucketStore) LabelValues(ctx context.Context, req *storepb.LabelValuesR
 
 	s.mtx.RUnlock()
 
+	defer func() {
+		if s.debugLogging {
+			level.Debug(logger).Log("msg", "stats query processed",
+				"request", req,
+				"tenant", tenant,
+				"stats", fmt.Sprintf("%+v", stats), "err", err)
+		}
+	}()
+
 	if err := g.Wait(); err != nil {
 		code := codes.Internal
 		if s, ok := status.FromError(errors.Cause(err)); ok {