Improving "Sparse postings" intersection (#13971)

Lets take the given example:

P1: [2, 5, 9, 18, 21]
P2: [3, 7, 14, 19, 21]
P3: [1, 21]

Currently, we would only advance through P1 and P2 until discovering
an intersection and then checking P3. In essence, the traversal order
was: 2, 3, 5, 7, 9, 14, 18, 19, 21 (intersection found).

With the proposed change, P3 is also examined even if P1 and P2
haven't found an intersection yet. This adjustment allows for the
possibility of skipping some iterations.

Post-change, the traversal order becomes: 2, 3, 21 (3 iterations instead of 9).

Signed-off-by: alanprot <alanprot@gmail.com>

tsdb/index/postings.go

@@ -620,18 +620,22 @@ func (it *intersectPostings) At() storage.SeriesRef {
 }
 
 func (it *intersectPostings) doNext() bool {
-Loop:
 	for {
+		allEqual := true
 		for _, p := range it.arr {
 			if !p.Seek(it.cur) {
 				return false
 			}
 			if p.At() > it.cur {
 				it.cur = p.At()
-				continue Loop
+				allEqual = false
 			}
 		}
-		return true
+
+		// if all p.At() are all equal, we found an intersection.
+		if allEqual {
+			return true
+		}
 	}
 }
 

tsdb/querier_bench_test.go

@@ -47,6 +47,7 @@ func BenchmarkQuerier(b *testing.B) {
 	}
 
 	for n := 0; n < 10; n++ {
+		addSeries(labels.FromStrings("a", strconv.Itoa(n)+postingsBenchSuffix))
 		for i := 0; i < 100000; i++ {
 			addSeries(labels.FromStrings("i", strconv.Itoa(i)+postingsBenchSuffix, "n", strconv.Itoa(n)+postingsBenchSuffix, "j", "foo"))
 			// Have some series that won't be matched, to properly test inverted matches.
@@ -101,7 +102,9 @@ func BenchmarkQuerier(b *testing.B) {
 func benchmarkPostingsForMatchers(b *testing.B, ir IndexReader) {
 	ctx := context.Background()
 
+	a1 := labels.MustNewMatcher(labels.MatchEqual, "a", "1"+postingsBenchSuffix)
 	n1 := labels.MustNewMatcher(labels.MatchEqual, "n", "1"+postingsBenchSuffix)
+	n0_1 := labels.MustNewMatcher(labels.MatchEqual, "n", "0_1"+postingsBenchSuffix)
 	nX := labels.MustNewMatcher(labels.MatchEqual, "n", "X"+postingsBenchSuffix)
 
 	jFoo := labels.MustNewMatcher(labels.MatchEqual, "j", "foo")
@@ -137,6 +140,7 @@ func benchmarkPostingsForMatchers(b *testing.B, ir IndexReader) {
 		{`j="foo",n="1"`, []*labels.Matcher{jFoo, n1}},
 		{`n="1",j!="foo"`, []*labels.Matcher{n1, jNotFoo}},
 		{`n="1",i!="2"`, []*labels.Matcher{n1, iNot2}},
+		{`n="0_1",j="foo,a="1"`, []*labels.Matcher{n0_1, jFoo, a1}},
 		{`n="X",j!="foo"`, []*labels.Matcher{nX, jNotFoo}},
 		{`i=~"1[0-9]",j=~"foo|bar"`, []*labels.Matcher{iCharSet, jFooBar}},
 		{`j=~"foo|bar"`, []*labels.Matcher{jFooBar}},
@@ -176,8 +180,12 @@ func benchmarkPostingsForMatchers(b *testing.B, ir IndexReader) {
 			b.ReportAllocs()
 			b.ResetTimer()
 			for i := 0; i < b.N; i++ {
-				_, err := PostingsForMatchers(ctx, ir, c.matchers...)
+				p, err := PostingsForMatchers(ctx, ir, c.matchers...)
 				require.NoError(b, err)
+				// Iterate over the postings
+				for p.Next() {
+					// Do nothing
+				}
 			}
 		})
 	}