Optimize labelValuesWithMatchers to fetch label values from selected series (#518)

* Optimize labelValues when matchers select small number of series. Signed-off-by: Peter Štibraný <pstibrany@gmail.com> * Address review feedback. Signed-off-by: Peter Štibraný <pstibrany@gmail.com> * Add missing p.Err() Signed-off-by: Peter Štibraný <pstibrany@gmail.com> * Reuse existing slice with all label values. Signed-off-by: Peter Štibraný <pstibrany@gmail.com> * Simplify check for expanded postings. Signed-off-by: Peter Štibraný <pstibrany@gmail.com> * Fix comment. Signed-off-by: Peter Štibraný <pstibrany@gmail.com> --------- Signed-off-by: Peter Štibraný <pstibrany@gmail.com>
2025-01-12 22:37:27 -08:00 · 2023-07-27 11:44:29 +02:00 · 2023-07-27 11:44:29 +02:00 · c8f5ad1492
parent 2a075ced62
commit c8f5ad1492
3 changed files with 226 additions and 1 deletions
--- a/tsdb/querier.go
+++ b/tsdb/querier.go
@ -346,6 +346,8 @@ func inversePostingsForMatcher(ix IndexPostingsReader, m *labels.Matcher) (index
 	return ix.Postings(m.Name, res...)
 }

+const maxExpandedPostingsFactor = 100 // Division factor for maximum number of matched series.
+
 func labelValuesWithMatchers(r IndexReader, name string, matchers ...*labels.Matcher) ([]string, error) {
 	p, err := PostingsForMatchers(r, matchers...)
 	if err != nil {
@ -376,6 +378,34 @@ func labelValuesWithMatchers(r IndexReader, name string, matchers ...*labels.Mat
 		allValues = filteredValues
 	}

+	// Let's see if expanded postings for matchers have smaller cardinality than label values.
+	// Since computing label values from series is expensive, we apply a limit on number of expanded
+	// postings (and series).
+	maxExpandedPostings := len(allValues) / maxExpandedPostingsFactor
+	if maxExpandedPostings > 0 {
+		// Add space for one extra posting when checking if we expanded all postings.
+		expanded := make([]storage.SeriesRef, 0, maxExpandedPostings+1)
+
+		// Call p.Next() even if len(expanded) == maxExpandedPostings. This tells us if there are more postings or not.
+		for len(expanded) <= maxExpandedPostings && p.Next() {
+			expanded = append(expanded, p.At())
+		}
+
+		if len(expanded) <= maxExpandedPostings {
+			// When we're here, p.Next() must have returned false, so we need to check for errors.
+			if err := p.Err(); err != nil {
+				return nil, errors.Wrap(err, "expanding postings for matchers")
+			}
+
+			// We have expanded all the postings -- all returned label values will be from these series only.
+			// (We supply allValues as a buffer for storing results. It should be big enough already, since it holds all possible label values.)
+			return labelValuesFromSeries(r, name, expanded, allValues)
+		}
+
+		// If we haven't reached end of postings, we prepend our expanded postings to "p", and continue.
+		p = newPrependPostings(expanded, p)
+	}
+
 	valuesPostings := make([]index.Postings, len(allValues))
 	for i, value := range allValues {
 		valuesPostings[i], err = r.Postings(name, value)
@ -396,6 +426,83 @@ func labelValuesWithMatchers(r IndexReader, name string, matchers ...*labels.Mat
 	return values, nil
 }

+// labelValuesFromSeries returns all unique label values from for given label name from supplied series. Values are not sorted.
+// buf is space for holding result (if it isn't big enough, it will be ignored), may be nil.
+func labelValuesFromSeries(r IndexReader, labelName string, refs []storage.SeriesRef, buf []string) ([]string, error) {
+	values := map[string]struct{}{}
+
+	var builder labels.ScratchBuilder
+	for _, ref := range refs {
+		err := r.Series(ref, &builder, nil)
+		if err != nil {
+			return nil, errors.Wrapf(err, "label values for label %s", labelName)
+		}
+
+		v := builder.Labels().Get(labelName)
+		if v != "" {
+			values[v] = struct{}{}
+		}
+	}
+
+	if cap(buf) >= len(values) {
+		buf = buf[:0]
+	} else {
+		buf = make([]string, 0, len(values))
+	}
+	for v := range values {
+		buf = append(buf, v)
+	}
+	return buf, nil
+}
+
+func newPrependPostings(a []storage.SeriesRef, b index.Postings) index.Postings {
+	return &prependPostings{
+		ix:     -1,
+		prefix: a,
+		rest:   b,
+	}
+}
+
+// prependPostings returns series references from "prefix" before using "rest" postings.
+type prependPostings struct {
+	ix     int
+	prefix []storage.SeriesRef
+	rest   index.Postings
+}
+
+func (p *prependPostings) Next() bool {
+	p.ix++
+	if p.ix < len(p.prefix) {
+		return true
+	}
+	return p.rest.Next()
+}
+
+func (p *prependPostings) Seek(v storage.SeriesRef) bool {
+	for p.ix < len(p.prefix) {
+		if p.ix >= 0 && p.prefix[p.ix] >= v {
+			return true
+		}
+		p.ix++
+	}
+
+	return p.rest.Seek(v)
+}
+
+func (p *prependPostings) At() storage.SeriesRef {
+	if p.ix >= 0 && p.ix < len(p.prefix) {
+		return p.prefix[p.ix]
+	}
+	return p.rest.At()
+}
+
+func (p *prependPostings) Err() error {
+	if p.ix >= 0 && p.ix < len(p.prefix) {
+		return nil
+	}
+	return p.rest.Err()
+}
+
 func labelNamesWithMatchers(r IndexReader, matchers ...*labels.Matcher) ([]string, error) {
 	p, err := r.PostingsForMatchers(false, matchers...)
 	if err != nil {
--- a/tsdb/querier_bench_test.go
+++ b/tsdb/querier_bench_test.go
@ -50,7 +50,7 @@ func BenchmarkQuerier(b *testing.B) {

 	for n := 0; n < 10; n++ {
 		for i := 0; i < 100000; i++ {
-			addSeries(labels.FromStrings("i", strconv.Itoa(i)+postingsBenchSuffix, "n", strconv.Itoa(n)+postingsBenchSuffix, "j", "foo"))
+			addSeries(labels.FromStrings("i", strconv.Itoa(i)+postingsBenchSuffix, "n", strconv.Itoa(n)+postingsBenchSuffix, "j", "foo", "i_times_n", strconv.Itoa(i*n)))
 			// Have some series that won't be matched, to properly test inverted matches.
 			addSeries(labels.FromStrings("i", strconv.Itoa(i)+postingsBenchSuffix, "n", strconv.Itoa(n)+postingsBenchSuffix, "j", "bar"))
 			addSeries(labels.FromStrings("i", strconv.Itoa(i)+postingsBenchSuffix, "n", "0_"+strconv.Itoa(n)+postingsBenchSuffix, "j", "bar"))
@ -184,6 +184,9 @@ func benchmarkLabelValuesWithMatchers(b *testing.B, ir IndexReader) {
 	n1 := labels.MustNewMatcher(labels.MatchEqual, "n", "1"+postingsBenchSuffix)
 	nX := labels.MustNewMatcher(labels.MatchNotEqual, "n", "X"+postingsBenchSuffix)
 	nPlus := labels.MustNewMatcher(labels.MatchRegexp, "i", "^.+$")
+	primesTimes := labels.MustNewMatcher(labels.MatchEqual, "i_times_n", "533701") // = 76243*7, ie. multiplication of primes. It will match single i*n combination.
+	nonPrimesTimes := labels.MustNewMatcher(labels.MatchEqual, "i_times_n", "20")  // 1*20, 2*10, 4*5, 5*4
+	times12 := labels.MustNewMatcher(labels.MatchRegexp, "i_times_n", "12.*")

 	cases := []struct {
 		name      string
@ -199,6 +202,9 @@ 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}},
+		{`i with i_times_n=533701`, "i", []*labels.Matcher{primesTimes}},
+		{`i with i_times_n=20`, "i", []*labels.Matcher{nonPrimesTimes}},
+		{`i with i_times_n=~"12.*""`, "i", []*labels.Matcher{times12}},
 		// n has 10 values.
 		{`n with j!="foo"`, "n", []*labels.Matcher{jNotFoo}},
 		{`n with i="1"`, "n", []*labels.Matcher{i1}},
--- a/tsdb/querier_test.go
+++ b/tsdb/querier_test.go
@ -2733,3 +2733,115 @@ func TestQueryWithDeletedHistograms(t *testing.T) {
 		})
 	}
 }
+
+func TestPrependPostings(t *testing.T) {
+	t.Run("empty", func(t *testing.T) {
+		p := newPrependPostings(nil, index.NewListPostings(nil))
+		require.False(t, p.Next())
+	})
+
+	t.Run("next+At", func(t *testing.T) {
+		p := newPrependPostings([]storage.SeriesRef{10, 20, 30}, index.NewListPostings([]storage.SeriesRef{200, 300, 500}))
+
+		for _, s := range []storage.SeriesRef{10, 20, 30, 200, 300, 500} {
+			require.True(t, p.Next())
+			require.Equal(t, s, p.At())
+			require.Equal(t, s, p.At()) // Multiple calls return same value.
+		}
+		require.False(t, p.Next())
+	})
+
+	t.Run("seek+At", func(t *testing.T) {
+		p := newPrependPostings([]storage.SeriesRef{10, 20, 30}, index.NewListPostings([]storage.SeriesRef{200, 300, 500}))
+
+		require.True(t, p.Seek(5))
+		require.Equal(t, storage.SeriesRef(10), p.At())
+		require.Equal(t, storage.SeriesRef(10), p.At())
+
+		require.True(t, p.Seek(15))
+		require.Equal(t, storage.SeriesRef(20), p.At())
+		require.Equal(t, storage.SeriesRef(20), p.At())
+
+		require.True(t, p.Seek(20)) // Seeking to "current" value doesn't move postings iterator.
+		require.Equal(t, storage.SeriesRef(20), p.At())
+		require.Equal(t, storage.SeriesRef(20), p.At())
+
+		require.True(t, p.Seek(50))
+		require.Equal(t, storage.SeriesRef(200), p.At())
+		require.Equal(t, storage.SeriesRef(200), p.At())
+
+		require.False(t, p.Seek(1000))
+		require.False(t, p.Next())
+	})
+
+	t.Run("err", func(t *testing.T) {
+		err := fmt.Errorf("error")
+		p := newPrependPostings([]storage.SeriesRef{10, 20, 30}, index.ErrPostings(err))
+
+		for _, s := range []storage.SeriesRef{10, 20, 30} {
+			require.True(t, p.Next())
+			require.Equal(t, s, p.At())
+			require.NoError(t, p.Err())
+		}
+		// Advancing after prepended values returns false, and gives us access to error.
+		require.False(t, p.Next())
+		require.Equal(t, err, p.Err())
+	})
+}
+
+func TestLabelsValuesWithMatchersOptimization(t *testing.T) {
+	dir := t.TempDir()
+	opts := DefaultHeadOptions()
+	opts.ChunkRange = 1000
+	opts.ChunkDirRoot = dir
+	h, err := NewHead(nil, nil, nil, nil, opts, nil)
+	require.NoError(t, err)
+	defer func() {
+		require.NoError(t, h.Close())
+	}()
+
+	app := h.Appender(context.Background())
+	addSeries := func(l labels.Labels) {
+		app.Append(0, l, 0, 0)
+	}
+
+	const maxI = 10 * maxExpandedPostingsFactor
+
+	allValuesOfI := make([]string, 0, maxI)
+	for i := 0; i < maxI; i++ {
+		allValuesOfI = append(allValuesOfI, strconv.Itoa(i))
+	}
+
+	for n := 0; n < 10; n++ {
+		for i := 0; i < maxI; i++ {
+			addSeries(labels.FromStrings("i", allValuesOfI[i], "n", strconv.Itoa(n), "j", "foo", "i_times_n", strconv.Itoa(i*n)))
+		}
+	}
+	require.NoError(t, app.Commit())
+
+	ir, err := h.Index()
+	require.NoError(t, err)
+
+	primesTimes := labels.MustNewMatcher(labels.MatchEqual, "i_times_n", "23") // It will match single i*n combination (n < 10)
+	nonPrimesTimes := labels.MustNewMatcher(labels.MatchEqual, "i_times_n", "20")
+	n3 := labels.MustNewMatcher(labels.MatchEqual, "n", "3")
+
+	cases := []struct {
+		name            string
+		labelName       string
+		matchers        []*labels.Matcher
+		expectedResults []string
+	}{
+		{name: `i with i_times_n=23`, labelName: "i", matchers: []*labels.Matcher{primesTimes}, expectedResults: []string{"23"}},
+		{name: `i with i_times_n=20`, labelName: "i", matchers: []*labels.Matcher{nonPrimesTimes}, expectedResults: []string{"4", "5", "10", "20"}},
+		{name: `n with n="3"`, labelName: "i", matchers: []*labels.Matcher{n3}, expectedResults: allValuesOfI},
+	}
+
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			values, err := labelValuesWithMatchers(ir, c.labelName, c.matchers...)
+			require.NoError(t, err)
+			require.ElementsMatch(t, c.expectedResults, values)
+		})
+	}
+}