fix: Improve execution speed for queries with label filters (#13922)

Co-authored-by: Travis Patterson <travis.patterson@grafana.com>

pkg/logql/syntax/ast.go

@@ -133,53 +133,54 @@ func (m MultiStageExpr) stages() ([]log.Stage, error) {
 // are as close to the front of the filter as possible.
 func (m MultiStageExpr) reorderStages() []StageExpr {
 	var (
-		result  = make([]StageExpr, 0, len(m))
-		filters = make([]*LineFilterExpr, 0, len(m))
-		rest    = make([]StageExpr, 0, len(m))
+		result         = make([]StageExpr, 0, len(m))
+		lineFilters    = make([]*LineFilterExpr, 0, len(m))
+		notLineFilters = make([]StageExpr, 0, len(m))
 	)
 
+	combineFilters := func() {
+		if len(lineFilters) > 0 {
+			result = append(result, combineFilters(lineFilters))
+		}
+
+		result = append(result, notLineFilters...)
+
+		lineFilters = lineFilters[:0]
+		notLineFilters = notLineFilters[:0]
+	}
+
 	for _, s := range m {
 		switch f := s.(type) {
+		case *LabelFilterExpr:
+			combineFilters()
+			result = append(result, f)
 		case *LineFilterExpr:
-			filters = append(filters, f)
+			lineFilters = append(lineFilters, f)
 		case *LineFmtExpr:
 			// line_format modifies the contents of the line so any line filter
 			// originally after a line_format must still be after the same
 			// line_format.
 
-			rest = append(rest, f)
+			notLineFilters = append(notLineFilters, f)
 
-			if len(filters) > 0 {
-				result = append(result, combineFilters(filters))
-			}
-			result = append(result, rest...)
-
-			filters = filters[:0]
-			rest = rest[:0]
+			combineFilters()
 		case *LabelParserExpr:
-			rest = append(rest, f)
+			notLineFilters = append(notLineFilters, f)
 
 			// unpack modifies the contents of the line so any line filter
 			// originally after an unpack must still be after the same
 			// unpack.
 			if f.Op == OpParserTypeUnpack {
-				if len(filters) > 0 {
-					result = append(result, combineFilters(filters))
-				}
-				result = append(result, rest...)
-
-				filters = filters[:0]
-				rest = rest[:0]
+				combineFilters()
 			}
 		default:
-			rest = append(rest, f)
+			notLineFilters = append(notLineFilters, f)
 		}
 	}
 
-	if len(filters) > 0 {
-		result = append(result, combineFilters(filters))
-	}
-	return append(result, rest...)
+	combineFilters()
+
+	return result
 }
 
 func combineFilters(in []*LineFilterExpr) StageExpr {

pkg/logql/syntax/ast_test.go

@@ -988,7 +988,7 @@ func Test_MergeBinOpVectors_Filter(t *testing.T) {
 	require.Equal(t, &promql.Sample{F: 2}, res)
 }
 
-func TestFilterReodering(t *testing.T) {
+func TestFilterReordering(t *testing.T) {
 	t.Run("it makes sure line filters are as early in the pipeline stages as possible", func(t *testing.T) {
 		logExpr := `{container_name="app"} |= "foo" |= "next" | logfmt |="bar" |="baz" | line_format "{{.foo}}" |="1" |="2" | logfmt |="3"`
 		l, err := ParseExpr(logExpr)
@@ -1008,6 +1008,36 @@ func TestFilterReodering(t *testing.T) {
 		require.Len(t, stages, 5)
 		require.Equal(t, `|= "06497595" | unpack != "message" | json | line_format "new log: {{.foo}}"`, MultiStageExpr(stages).String())
 	})
+
+	t.Run("it makes sure label filter order is kept", func(t *testing.T) {
+		logExpr := `{container_name="app"} | bar="next" |= "foo" | logfmt |="bar" |="baz" | line_format "{{.foo}}" |="1" |="2" | logfmt |="3"`
+		l, err := ParseExpr(logExpr)
+		require.NoError(t, err)
+
+		stages := l.(*PipelineExpr).MultiStages.reorderStages()
+		require.Len(t, stages, 6)
+		require.Equal(t, `| bar="next" |= "foo" |= "bar" |= "baz" | logfmt | line_format "{{.foo}}" |= "1" |= "2" |= "3" | logfmt`, MultiStageExpr(stages).String())
+	})
+
+	t.Run("it makes sure line filters before labels filters keeps correct ordering", func(t *testing.T) {
+		logExpr := `{container_name="app"} |= "foo" |bar="next"`
+		l, err := ParseExpr(logExpr)
+		require.NoError(t, err)
+
+		stages := l.(*PipelineExpr).MultiStages.reorderStages()
+		require.Len(t, stages, 2)
+		require.Equal(t, `|= "foo" | bar="next"`, MultiStageExpr(stages).String())
+	})
+
+	t.Run("it makes sure json before label filter keeps correct ordering", func(t *testing.T) {
+		logExpr := `{container_name="app"} | json | bar="next"`
+		l, err := ParseExpr(logExpr)
+		require.NoError(t, err)
+
+		stages := l.(*PipelineExpr).MultiStages.reorderStages()
+		require.Len(t, stages, 2)
+		require.Equal(t, `| json | bar="next"`, MultiStageExpr(stages).String())
+	})
 }
 
 var result bool