TSDB: Fix up LabelValues to work for OOO-only head

Signed-off-by: Bryan Boreham <bjboreham@gmail.com>

tsdb/ooo_head_read.go

@@ -627,6 +627,20 @@ func (oh *HeadAndOOOIndexReader) Series(ref storage.SeriesRef, builder *labels.S
 	return nil
 }
 
+// LabelValues needs to be overridden from the headIndexReader implementation
+// so we can return labels within either in-order range or ooo range.
+func (oh *HeadAndOOOIndexReader) LabelValues(ctx context.Context, name string, matchers ...*labels.Matcher) ([]string, error) {
+	if oh.maxt < oh.head.MinTime() && oh.maxt < oh.head.MinOOOTime() || oh.mint > oh.head.MaxTime() && oh.mint > oh.head.MaxOOOTime() {
+		return []string{}, nil
+	}
+
+	if len(matchers) == 0 {
+		return oh.head.postings.LabelValues(ctx, name), nil
+	}
+
+	return labelValuesWithMatchers(ctx, oh, name, matchers...)
+}
+
 type HeadAndOOOChunkReader struct {
 	head        *Head
 	mint, maxt  int64

tsdb/ooo_head_read_test.go

@@ -421,17 +421,17 @@ func testOOOHeadChunkReader_LabelValues(t *testing.T, scenario sampleTypeScenari
 			name:       "LabelValues calls with ooo head query range not overlapping out-of-order data",
 			queryMinT:  100,
 			queryMaxT:  100,
-			expValues1: []string{},
-			expValues2: []string{},
-			expValues3: []string{},
-			expValues4: []string{},
+			expValues1: []string{"bar1"},
+			expValues2: nil,
+			expValues3: []string{"bar1", "bar2"},
+			expValues4: []string{"bar1", "bar2"},
 		},
 	}
 
 	for _, tc := range cases {
 		t.Run(tc.name, func(t *testing.T) {
 			// We first want to test using a head index reader that covers the biggest query interval
-			oh := NewOOOHeadIndexReader(head, tc.queryMinT, tc.queryMaxT, 0)
+			oh := NewHeadAndOOOIndexReader(head, tc.queryMinT, tc.queryMaxT, 0)
 			matchers := []*labels.Matcher{labels.MustNewMatcher(labels.MatchEqual, "foo", "bar1")}
 			values, err := oh.LabelValues(ctx, "foo", matchers...)
 			sort.Strings(values)