Avoid line copy during LogQL line_format

pkg/logql/log/fmt.go

@@ -131,10 +131,7 @@ func (lf *LineFormatter) Process(line []byte, lbs *LabelsBuilder) ([]byte, bool)
 		lbs.SetErr(errTemplateFormat)
 		return line, true
 	}
-	// todo(cyriltovena): we might want to reuse the input line or a bytes buffer.
-	res := make([]byte, len(lf.buf.Bytes()))
-	copy(res, lf.buf.Bytes())
-	return res, true
+	return lf.buf.Bytes(), true
 }
 
 func (lf *LineFormatter) RequiredLabelNames() []string {

pkg/logql/log/pipeline.go

@@ -19,6 +19,8 @@ type Pipeline interface {
 // A StreamPipeline never mutate the received line.
 type StreamPipeline interface {
 	BaseLabels() LabelsResult
+	// Process processes a log line and returns the transformed line and the labels.
+	// The buffer returned for the log line can be reused on subsequent calls to Process and therefore must be copied.
 	Process(ts int64, line []byte) (resultLine []byte, resultLabels LabelsResult, matches bool)
 	ProcessString(ts int64, line string) (resultLine string, resultLabels LabelsResult, matches bool)
 }
@@ -149,11 +151,9 @@ func (p *streamPipeline) Process(_ int64, line []byte) ([]byte, LabelsResult, bo
 
 func (p *streamPipeline) ProcessString(ts int64, line string) (string, LabelsResult, bool) {
 	// Stages only read from the line.
-	lb := unsafeGetBytes(line)
-	lb, lr, ok := p.Process(ts, lb)
-	// either the line is unchanged and we can just send back the same string.
-	// or we created a new buffer for it in which case it is still safe to avoid the string(byte) copy.
-	return unsafeGetString(lb), lr, ok
+	lb, lr, ok := p.Process(ts, unsafeGetBytes(line))
+	// but the returned line needs to be copied.
+	return string(lb), lr, ok
 }
 
 func (p *streamPipeline) BaseLabels() LabelsResult { return p.builder.currentResult }

pkg/logql/syntax/parser_test.go

@@ -3050,6 +3050,65 @@ func Test_PipelineCombined(t *testing.T) {
 	require.Equal(t, string([]byte(`1.5s|POST|200`)), string(line))
 }
 
+func Benchmark_PipelineCombined(b *testing.B) {
+	query := `{job="cortex-ops/query-frontend"} |= "logging.go" | logfmt | line_format "{{.msg}}" | regexp "(?P<method>\\w+) (?P<path>[\\w|/]+) \\((?P<status>\\d+?)\\) (?P<duration>.*)" | (duration > 1s or status==200) and method="POST" | line_format "{{.duration}}|{{.method}}|{{.status}}"`
+
+	expr, err := ParseLogSelector(query, true)
+	require.Nil(b, err)
+
+	p, err := expr.Pipeline()
+	require.Nil(b, err)
+	sp := p.ForStream(labels.Labels{})
+	var (
+		line    []byte
+		lbs     log.LabelsResult
+		matches bool
+	)
+	in := []byte(`level=debug ts=2020-10-02T10:10:42.092268913Z caller=logging.go:66 traceID=a9d4d8a928d8db1 msg="POST /api/prom/api/v1/query_range (200) 1.5s"`)
+
+	b.ReportAllocs()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		line, lbs, matches = sp.Process(0, in)
+	}
+	require.True(b, matches)
+	require.Equal(
+		b,
+		labels.Labels{labels.Label{Name: "caller", Value: "logging.go:66"}, labels.Label{Name: "duration", Value: "1.5s"}, labels.Label{Name: "level", Value: "debug"}, labels.Label{Name: "method", Value: "POST"}, labels.Label{Name: "msg", Value: "POST /api/prom/api/v1/query_range (200) 1.5s"}, labels.Label{Name: "path", Value: "/api/prom/api/v1/query_range"}, labels.Label{Name: "status", Value: "200"}, labels.Label{Name: "traceID", Value: "a9d4d8a928d8db1"}, labels.Label{Name: "ts", Value: "2020-10-02T10:10:42.092268913Z"}},
+		lbs.Labels(),
+	)
+	require.Equal(b, string([]byte(`1.5s|POST|200`)), string(line))
+}
+
+func Benchmark_MetricPipelineCombined(b *testing.B) {
+	query := `count_over_time({job="cortex-ops/query-frontend"} |= "logging.go" | logfmt | line_format "{{.msg}}" | regexp "(?P<method>\\w+) (?P<path>[\\w|/]+) \\((?P<status>\\d+?)\\) (?P<duration>.*)" | (duration > 1s or status==200) and method="POST" | line_format "{{.duration}}|{{.method}}|{{.status}}"[1m])`
+
+	expr, err := ParseSampleExpr(query)
+	require.Nil(b, err)
+
+	p, err := expr.Extractor()
+	require.Nil(b, err)
+	sp := p.ForStream(labels.Labels{})
+	var (
+		v       float64
+		lbs     log.LabelsResult
+		matches bool
+	)
+	in := []byte(`level=debug ts=2020-10-02T10:10:42.092268913Z caller=logging.go:66 traceID=a9d4d8a928d8db1 msg="POST /api/prom/api/v1/query_range (200) 1.5s"`)
+	b.ReportAllocs()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		v, lbs, matches = sp.Process(0, in)
+	}
+	require.True(b, matches)
+	require.Equal(
+		b,
+		labels.Labels{labels.Label{Name: "caller", Value: "logging.go:66"}, labels.Label{Name: "duration", Value: "1.5s"}, labels.Label{Name: "level", Value: "debug"}, labels.Label{Name: "method", Value: "POST"}, labels.Label{Name: "msg", Value: "POST /api/prom/api/v1/query_range (200) 1.5s"}, labels.Label{Name: "path", Value: "/api/prom/api/v1/query_range"}, labels.Label{Name: "status", Value: "200"}, labels.Label{Name: "traceID", Value: "a9d4d8a928d8db1"}, labels.Label{Name: "ts", Value: "2020-10-02T10:10:42.092268913Z"}},
+		lbs.Labels(),
+	)
+	require.Equal(b, 1.0, v)
+}
+
 var c []*labels.Matcher
 
 func Benchmark_ParseMatchers(b *testing.B) {