Optimize label values with matchers by taking shortcuts (#13426)

Don't calculate postings beforehand: we may not need them. If all
matchers are for the requested label, we can just filter its values.

Also, if there are no values at all, no need to run any kind of
logic.

Also add more labelValuesWithMatchers benchmarks

Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>

tsdb/ooo_head_read_test.go

@@ -410,7 +410,7 @@ func TestOOOHeadChunkReader_LabelValues(t *testing.T) {
 			queryMinT:  math.MinInt64,
 			queryMaxT:  math.MaxInt64,
 			expValues1: []string{"bar1"},
-			expValues2: []string{},
+			expValues2: nil,
 			expValues3: []string{"bar1", "bar2"},
 			expValues4: []string{"bar1", "bar2"},
 		},
@@ -419,7 +419,7 @@ func TestOOOHeadChunkReader_LabelValues(t *testing.T) {
 			queryMinT:  90,
 			queryMaxT:  90,
 			expValues1: []string{"bar1"},
-			expValues2: []string{},
+			expValues2: nil,
 			expValues3: []string{"bar1", "bar2"},
 			expValues4: []string{"bar1", "bar2"},
 		},

tsdb/querier.go

@@ -440,11 +440,6 @@ func inversePostingsForMatcher(ctx context.Context, ix IndexReader, m *labels.Ma
 }
 
 func labelValuesWithMatchers(ctx context.Context, r IndexReader, name string, matchers ...*labels.Matcher) ([]string, error) {
-	p, err := PostingsForMatchers(ctx, r, matchers...)
-	if err != nil {
-		return nil, fmt.Errorf("fetching postings for matchers: %w", err)
-	}
-
 	allValues, err := r.LabelValues(ctx, name)
 	if err != nil {
 		return nil, fmt.Errorf("fetching values of label %s: %w", name, err)
@@ -453,8 +448,10 @@ func labelValuesWithMatchers(ctx context.Context, r IndexReader, name string, ma
 	// If we have a matcher for the label name, we can filter out values that don't match
 	// before we fetch postings. This is especially useful for labels with many values.
 	// e.g. __name__ with a selector like {__name__="xyz"}
+	hasMatchersForOtherLabels := false
 	for _, m := range matchers {
 		if m.Name != name {
+			hasMatchersForOtherLabels = true
 			continue
 		}
 
@@ -469,6 +466,20 @@ func labelValuesWithMatchers(ctx context.Context, r IndexReader, name string, ma
 		allValues = filteredValues
 	}
 
+	if len(allValues) == 0 {
+		return nil, nil
+	}
+
+	// If we don't have any matchers for other labels, then we're done.
+	if !hasMatchersForOtherLabels {
+		return allValues, nil
+	}
+
+	p, err := PostingsForMatchers(ctx, r, matchers...)
+	if err != nil {
+		return nil, fmt.Errorf("fetching postings for matchers: %w", err)
+	}
+
 	valuesPostings := make([]index.Postings, len(allValues))
 	for i, value := range allValues {
 		valuesPostings[i], err = r.Postings(ctx, name, value)

tsdb/querier_bench_test.go

@@ -182,13 +182,16 @@ func benchmarkPostingsForMatchers(b *testing.B, ir IndexReader) {
 
 func benchmarkLabelValuesWithMatchers(b *testing.B, ir IndexReader) {
 	i1 := labels.MustNewMatcher(labels.MatchEqual, "i", "1")
+	i1Plus := labels.MustNewMatcher(labels.MatchRegexp, "i", "1.+")
+	i1PostingsBenchSuffix := labels.MustNewMatcher(labels.MatchEqual, "i", "1"+postingsBenchSuffix)
+	iSuffix := labels.MustNewMatcher(labels.MatchRegexp, "i", ".+ddd")
 	iStar := labels.MustNewMatcher(labels.MatchRegexp, "i", "^.*$")
 	jNotFoo := labels.MustNewMatcher(labels.MatchNotEqual, "j", "foo")
 	jXXXYYY := labels.MustNewMatcher(labels.MatchRegexp, "j", "XXX|YYY")
 	jXplus := labels.MustNewMatcher(labels.MatchRegexp, "j", "X.+")
 	n1 := labels.MustNewMatcher(labels.MatchEqual, "n", "1"+postingsBenchSuffix)
 	nX := labels.MustNewMatcher(labels.MatchNotEqual, "n", "X"+postingsBenchSuffix)
-	nPlus := labels.MustNewMatcher(labels.MatchRegexp, "i", "^.+$")
+	nPlus := labels.MustNewMatcher(labels.MatchRegexp, "n", "^.+$")
 
 	ctx := context.Background()
 
@@ -197,6 +200,7 @@ func benchmarkLabelValuesWithMatchers(b *testing.B, ir IndexReader) {
 		labelName string
 		matchers  []*labels.Matcher
 	}{
+		// i is never "1", this isn't matching anything.
 		{`i with i="1"`, "i", []*labels.Matcher{i1}},
 		// i has 100k values.
 		{`i with n="1"`, "i", []*labels.Matcher{n1}},
@@ -206,9 +210,16 @@ func benchmarkLabelValuesWithMatchers(b *testing.B, ir IndexReader) {
 		{`i with n="1",j=~"XXX|YYY"`, "i", []*labels.Matcher{n1, jXXXYYY}},
 		{`i with n="X",j!="foo"`, "i", []*labels.Matcher{nX, jNotFoo}},
 		{`i with n="1",i=~"^.*$",j!="foo"`, "i", []*labels.Matcher{n1, iStar, jNotFoo}},
+		// matchers on i itself
+		{`i with i="1aaa...ddd"`, "i", []*labels.Matcher{i1PostingsBenchSuffix}},
+		{`i with i=~"1.+"`, "i", []*labels.Matcher{i1Plus}},
+		{`i with i=~"1.+",i=~".+ddd"`, "i", []*labels.Matcher{i1Plus, iSuffix}},
 		// n has 10 values.
 		{`n with j!="foo"`, "n", []*labels.Matcher{jNotFoo}},
 		{`n with i="1"`, "n", []*labels.Matcher{i1}},
+		{`n with i=~"1.+"`, "n", []*labels.Matcher{i1Plus}},
+		// there's no label "none"
+		{`none with i=~"1"`, "none", []*labels.Matcher{i1Plus}},
 	}
 
 	for _, c := range cases {