From 8c5d4b4add2c528701cced254d1272824b9ec3ba Mon Sep 17 00:00:00 2001
From: Alan Protasio <alanprot@gmail.com>
Date: Sun, 21 May 2023 01:41:30 -0700
Subject: [PATCH] Opmize MatchNotEqual (#12377)

Signed-off-by: Alan Protasio <alanprot@gmail.com>
---
 tsdb/querier.go            | 24 ++++++++++++++++--------
 tsdb/querier_bench_test.go |  1 +
 2 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/tsdb/querier.go b/tsdb/querier.go
index 8bcd451f3..9baf3f242 100644
--- a/tsdb/querier.go
+++ b/tsdb/querier.go
@@ -361,6 +361,22 @@ func postingsForMatcher(ix IndexReader, m *labels.Matcher) (index.Postings, erro
 
 // inversePostingsForMatcher returns the postings for the series with the label name set but not matching the matcher.
 func inversePostingsForMatcher(ix IndexReader, m *labels.Matcher) (index.Postings, error) {
+	// Fast-path for MatchNotRegexp matching.
+	// Inverse of a MatchNotRegexp is MatchRegexp (double negation).
+	// Fast-path for set matching.
+	if m.Type == labels.MatchNotRegexp {
+		setMatches := findSetMatches(m.GetRegexString())
+		if len(setMatches) > 0 {
+			return ix.Postings(m.Name, setMatches...)
+		}
+	}
+
+	// Fast-path for MatchNotEqual matching.
+	// Inverse of a MatchNotEqual is MatchEqual (double negation).
+	if m.Type == labels.MatchNotEqual {
+		return ix.Postings(m.Name, m.Value)
+	}
+
 	vals, err := ix.LabelValues(m.Name)
 	if err != nil {
 		return nil, err
@@ -371,14 +387,6 @@ func inversePostingsForMatcher(ix IndexReader, m *labels.Matcher) (index.Posting
 	if m.Type == labels.MatchEqual && m.Value == "" {
 		res = vals
 	} else {
-		// Inverse of a MatchNotRegexp is MatchRegexp (double negation).
-		// Fast-path for set matching.
-		if m.Type == labels.MatchNotRegexp {
-			setMatches := findSetMatches(m.GetRegexString())
-			if len(setMatches) > 0 {
-				return ix.Postings(m.Name, setMatches...)
-			}
-		}
 		for _, val := range vals {
 			if !m.Matches(val) {
 				res = append(res, val)
diff --git a/tsdb/querier_bench_test.go b/tsdb/querier_bench_test.go
index 6e5243ef1..19619e35b 100644
--- a/tsdb/querier_bench_test.go
+++ b/tsdb/querier_bench_test.go
@@ -125,6 +125,7 @@ func benchmarkPostingsForMatchers(b *testing.B, ir IndexReader) {
 		{`n="X",j="foo"`, []*labels.Matcher{nX, jFoo}},
 		{`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="X",j!="foo"`, []*labels.Matcher{nX, jNotFoo}},
 		{`i=~"1[0-9]",j=~"foo|bar"`, []*labels.Matcher{iCharSet, jFooBar}},
 		{`j=~"foo|bar"`, []*labels.Matcher{jFooBar}},