Append Created Timestamps (#12733)

* Append created timestamps. Signed-off-by: Arthur Silva Sens <arthur.sens@coralogix.com> * Log when created timestamps are ignored Signed-off-by: Arthur Silva Sens <arthur.sens@coralogix.com> * Proposed changes to Append CT PR. Changes: * Changed textparse Parser interface for consistency and robustness. * Changed CT interface to be more explicit and handle validation. * Simplified test, change scrapeManager to allow testability. * Added TODOs. Signed-off-by: bwplotka <bwplotka@gmail.com> * Updates. Signed-off-by: bwplotka <bwplotka@gmail.com> * Addressed comments. Signed-off-by: bwplotka <bwplotka@gmail.com> * Refactor head_appender test Signed-off-by: Arthur Silva Sens <arthur.sens@coralogix.com> * Fix linter issues Signed-off-by: Arthur Silva Sens <arthur.sens@coralogix.com> * Use model.Sample in head appender test Signed-off-by: Arthur Silva Sens <arthur.sens@coralogix.com> --------- Signed-off-by: Arthur Silva Sens <arthur.sens@coralogix.com> Signed-off-by: bwplotka <bwplotka@gmail.com> Co-authored-by: bwplotka <bwplotka@gmail.com>
2 years ago · 5082655392
parent db915b07cb
commit 5082655392
21 changed files with 578 additions and 74 deletions
--- a/cmd/prometheus/main.go
+++ b/cmd/prometheus/main.go
@ -206,9 +206,15 @@ func (c *flagConfig) setFeatureListOptions(logger log.Logger) error {
 			case "native-histograms":
 				c.tsdb.EnableNativeHistograms = true
 				// Change relevant global variables. Hacky, but it's hard to pass a new option or default to unmarshallers.
-				config.DefaultConfig.GlobalConfig.ScrapeProtocols = config.DefaultNativeHistogramScrapeProtocols
-				config.DefaultGlobalConfig.ScrapeProtocols = config.DefaultNativeHistogramScrapeProtocols
+				config.DefaultConfig.GlobalConfig.ScrapeProtocols = config.DefaultProtoFirstScrapeProtocols
+				config.DefaultGlobalConfig.ScrapeProtocols = config.DefaultProtoFirstScrapeProtocols
 				level.Info(logger).Log("msg", "Experimental native histogram support enabled. Changed default scrape_protocols to prefer PrometheusProto format.", "global.scrape_protocols", fmt.Sprintf("%v", config.DefaultGlobalConfig.ScrapeProtocols))
+			case "created-timestamp-zero-ingestion":
+				c.scrape.EnableCreatedTimestampZeroIngestion = true
+				// Change relevant global variables. Hacky, but it's hard to pass a new option or default to unmarshallers.
+				config.DefaultConfig.GlobalConfig.ScrapeProtocols = config.DefaultProtoFirstScrapeProtocols
+				config.DefaultGlobalConfig.ScrapeProtocols = config.DefaultProtoFirstScrapeProtocols
+				level.Info(logger).Log("msg", "Experimental created timestamp zero ingestion enabled. Changed default scrape_protocols to prefer PrometheusProto format.", "global.scrape_protocols", fmt.Sprintf("%v", config.DefaultGlobalConfig.ScrapeProtocols))
 			case "":
 				continue
 			case "promql-at-modifier", "promql-negative-offset":
@ -1449,6 +1455,10 @@ func (n notReadyAppender) UpdateMetadata(ref storage.SeriesRef, l labels.Labels,
 	return 0, tsdb.ErrNotReady
 }

+func (n notReadyAppender) AppendCTZeroSample(ref storage.SeriesRef, l labels.Labels, t, ct int64) (storage.SeriesRef, error) {
+	return 0, tsdb.ErrNotReady
+}
+
 func (n notReadyAppender) Commit() error { return tsdb.ErrNotReady }

 func (n notReadyAppender) Rollback() error { return tsdb.ErrNotReady }
--- a/config/config.go
+++ b/config/config.go
@ -454,12 +454,19 @@ var (
 		OpenMetricsText1_0_0: "application/openmetrics-text;version=1.0.0",
 	}

+	// DefaultScrapeProtocols is the set of scrape protocols that will be proposed
+	// to scrape target, ordered by priority.
 	DefaultScrapeProtocols = []ScrapeProtocol{
 		OpenMetricsText1_0_0,
 		OpenMetricsText0_0_1,
 		PrometheusText0_0_4,
 	}
-	DefaultNativeHistogramScrapeProtocols = []ScrapeProtocol{
+
+	// DefaultProtoFirstScrapeProtocols is like DefaultScrapeProtocols, but it
+	// favors protobuf Prometheus exposition format.
+	// Used by default for certain feature-flags like
+	// "native-histograms" and "created-timestamp-zero-ingestion".
+	DefaultProtoFirstScrapeProtocols = []ScrapeProtocol{
 		PrometheusProto,
 		OpenMetricsText1_0_0,
 		OpenMetricsText0_0_1,
--- a/model/textparse/interface.go
+++ b/model/textparse/interface.go
@ -16,8 +16,6 @@ package textparse
 import (
 	"mime"

-	"github.com/gogo/protobuf/types"
-
 	"github.com/prometheus/prometheus/model/exemplar"
 	"github.com/prometheus/prometheus/model/histogram"
 	"github.com/prometheus/prometheus/model/labels"
@ -66,10 +64,10 @@ type Parser interface {
 	// retrieved (including the case where no exemplars exist at all).
 	Exemplar(l *exemplar.Exemplar) bool

-	// CreatedTimestamp writes the created timestamp of the current sample
-	// into the passed timestamp. It returns false if no created timestamp
-	// exists or if the metric type does not support created timestamps.
-	CreatedTimestamp(ct *types.Timestamp) bool
+	// CreatedTimestamp returns the created timestamp (in milliseconds) for the
+	// current sample. It returns nil if it is unknown e.g. if it wasn't set,
+	// if the scrape protocol or metric type does not support created timestamps.
+	CreatedTimestamp() *int64

 	// Next advances the parser to the next sample. It returns false if no
 	// more samples were read or an error occurred.
--- a/model/textparse/openmetricsparse.go
+++ b/model/textparse/openmetricsparse.go
@ -24,8 +24,6 @@ import (
 	"strings"
 	"unicode/utf8"

-	"github.com/gogo/protobuf/types"
-
 	"github.com/prometheus/prometheus/model/exemplar"
 	"github.com/prometheus/prometheus/model/histogram"
 	"github.com/prometheus/prometheus/model/labels"
@ -213,9 +211,10 @@ func (p *OpenMetricsParser) Exemplar(e *exemplar.Exemplar) bool {
 	return true
 }

-// CreatedTimestamp returns false because OpenMetricsParser does not support created timestamps (yet).
-func (p *OpenMetricsParser) CreatedTimestamp(_ *types.Timestamp) bool {
-	return false
+// CreatedTimestamp returns nil as it's not implemented yet.
+// TODO(bwplotka): https://github.com/prometheus/prometheus/issues/12980
+func (p *OpenMetricsParser) CreatedTimestamp() *int64 {
+	return nil
 }

 // nextToken returns the next token from the openMetricsLexer.
--- a/model/textparse/promparse.go
+++ b/model/textparse/promparse.go
@ -26,8 +26,6 @@ import (
 	"unicode/utf8"
 	"unsafe"

-	"github.com/gogo/protobuf/types"
-
 	"github.com/prometheus/prometheus/model/exemplar"
 	"github.com/prometheus/prometheus/model/histogram"
 	"github.com/prometheus/prometheus/model/labels"
@ -247,9 +245,10 @@ func (p *PromParser) Exemplar(*exemplar.Exemplar) bool {
 	return false
 }

-// CreatedTimestamp returns false because PromParser does not support created timestamps.
-func (p *PromParser) CreatedTimestamp(_ *types.Timestamp) bool {
-	return false
+// CreatedTimestamp returns nil as it's not implemented yet.
+// TODO(bwplotka): https://github.com/prometheus/prometheus/issues/12980
+func (p *PromParser) CreatedTimestamp() *int64 {
+	return nil
 }

 // nextToken returns the next token from the promlexer. It skips over tabs
--- a/model/textparse/protobufparse.go
+++ b/model/textparse/protobufparse.go
@ -360,22 +360,26 @@ func (p *ProtobufParser) Exemplar(ex *exemplar.Exemplar) bool {
 	return true
 }

-func (p *ProtobufParser) CreatedTimestamp(ct *types.Timestamp) bool {
-	var foundCT *types.Timestamp
+// CreatedTimestamp returns CT or nil if CT is not present or
+// invalid (as timestamp e.g. negative value) on counters, summaries or histograms.
+func (p *ProtobufParser) CreatedTimestamp() *int64 {
+	var ct *types.Timestamp
 	switch p.mf.GetType() {
 	case dto.MetricType_COUNTER:
-		foundCT = p.mf.GetMetric()[p.metricPos].GetCounter().GetCreatedTimestamp()
+		ct = p.mf.GetMetric()[p.metricPos].GetCounter().GetCreatedTimestamp()
 	case dto.MetricType_SUMMARY:
-		foundCT = p.mf.GetMetric()[p.metricPos].GetSummary().GetCreatedTimestamp()
+		ct = p.mf.GetMetric()[p.metricPos].GetSummary().GetCreatedTimestamp()
 	case dto.MetricType_HISTOGRAM, dto.MetricType_GAUGE_HISTOGRAM:
-		foundCT = p.mf.GetMetric()[p.metricPos].GetHistogram().GetCreatedTimestamp()
+		ct = p.mf.GetMetric()[p.metricPos].GetHistogram().GetCreatedTimestamp()
 	default:
 	}
-	if foundCT == nil {
-		return false
+	ctAsTime, err := types.TimestampFromProto(ct)
+	if err != nil {
+		// Errors means ct == nil or invalid timestamp, which we silently ignore.
+		return nil
 	}
-	*ct = *foundCT
-	return true
+	ctMilis := ctAsTime.UnixMilli()
+	return &ctMilis
 }

 // Next advances the parser to the next "sample" (emulating the behavior of a
--- a/model/textparse/protobufparse_test.go
+++ b/model/textparse/protobufparse_test.go
@ -21,7 +21,6 @@ import (
 	"testing"

 	"github.com/gogo/protobuf/proto"
-	"github.com/gogo/protobuf/types"
 	"github.com/stretchr/testify/require"

 	"github.com/prometheus/prometheus/model/exemplar"
@ -630,7 +629,7 @@ func TestProtobufParse(t *testing.T) {
 		shs     *histogram.Histogram
 		fhs     *histogram.FloatHistogram
 		e       []exemplar.Exemplar
-		ct      *types.Timestamp
+		ct      int64
 	}

 	inputBuf := createTestProtoBuf(t)
@ -1069,7 +1068,7 @@ func TestProtobufParse(t *testing.T) {
 				{
 					m:  "test_counter_with_createdtimestamp",
 					v:  42,
-					ct: &types.Timestamp{Seconds: 1, Nanos: 1},
+					ct: 1000,
 					lset: labels.FromStrings(
 						"__name__", "test_counter_with_createdtimestamp",
 					),
@ -1085,7 +1084,7 @@ func TestProtobufParse(t *testing.T) {
 				{
 					m:  "test_summary_with_createdtimestamp_count",
 					v:  42,
-					ct: &types.Timestamp{Seconds: 1, Nanos: 1},
+					ct: 1000,
 					lset: labels.FromStrings(
 						"__name__", "test_summary_with_createdtimestamp_count",
 					),
@ -1093,7 +1092,7 @@ func TestProtobufParse(t *testing.T) {
 				{
 					m:  "test_summary_with_createdtimestamp_sum",
 					v:  1.234,
-					ct: &types.Timestamp{Seconds: 1, Nanos: 1},
+					ct: 1000,
 					lset: labels.FromStrings(
 						"__name__", "test_summary_with_createdtimestamp_sum",
 					),
@ -1108,7 +1107,7 @@ func TestProtobufParse(t *testing.T) {
 				},
 				{
 					m:  "test_histogram_with_createdtimestamp",
-					ct: &types.Timestamp{Seconds: 1, Nanos: 1},
+					ct: 1000,
 					shs: &histogram.Histogram{
 						CounterResetHint: histogram.UnknownCounterReset,
 						PositiveSpans:    []histogram.Span{},
@ -1128,7 +1127,7 @@ func TestProtobufParse(t *testing.T) {
 				},
 				{
 					m:  "test_gaugehistogram_with_createdtimestamp",
-					ct: &types.Timestamp{Seconds: 1, Nanos: 1},
+					ct: 1000,
 					shs: &histogram.Histogram{
 						CounterResetHint: histogram.GaugeType,
 						PositiveSpans:    []histogram.Span{},
@ -1887,7 +1886,7 @@ func TestProtobufParse(t *testing.T) {
 				{ // 83
 					m:  "test_counter_with_createdtimestamp",
 					v:  42,
-					ct: &types.Timestamp{Seconds: 1, Nanos: 1},
+					ct: 1000,
 					lset: labels.FromStrings(
 						"__name__", "test_counter_with_createdtimestamp",
 					),
@ -1903,7 +1902,7 @@ func TestProtobufParse(t *testing.T) {
 				{ // 86
 					m:  "test_summary_with_createdtimestamp_count",
 					v:  42,
-					ct: &types.Timestamp{Seconds: 1, Nanos: 1},
+					ct: 1000,
 					lset: labels.FromStrings(
 						"__name__", "test_summary_with_createdtimestamp_count",
 					),
@ -1911,7 +1910,7 @@ func TestProtobufParse(t *testing.T) {
 				{ // 87
 					m:  "test_summary_with_createdtimestamp_sum",
 					v:  1.234,
-					ct: &types.Timestamp{Seconds: 1, Nanos: 1},
+					ct: 1000,
 					lset: labels.FromStrings(
 						"__name__", "test_summary_with_createdtimestamp_sum",
 					),
@ -1926,7 +1925,7 @@ func TestProtobufParse(t *testing.T) {
 				},
 				{ // 90
 					m:  "test_histogram_with_createdtimestamp",
-					ct: &types.Timestamp{Seconds: 1, Nanos: 1},
+					ct: 1000,
 					shs: &histogram.Histogram{
 						CounterResetHint: histogram.UnknownCounterReset,
 						PositiveSpans:    []histogram.Span{},
@ -1946,7 +1945,7 @@ func TestProtobufParse(t *testing.T) {
 				},
 				{ // 93
 					m:  "test_gaugehistogram_with_createdtimestamp",
-					ct: &types.Timestamp{Seconds: 1, Nanos: 1},
+					ct: 1000,
 					shs: &histogram.Histogram{
 						CounterResetHint: histogram.GaugeType,
 						PositiveSpans:    []histogram.Span{},
@ -1981,10 +1980,9 @@ func TestProtobufParse(t *testing.T) {
 					m, ts, v := p.Series()

 					var e exemplar.Exemplar
-					var ct types.Timestamp
 					p.Metric(&res)
 					eFound := p.Exemplar(&e)
-					ctFound := p.CreatedTimestamp(&ct)
+					ct := p.CreatedTimestamp()
 					require.Equal(t, exp[i].m, string(m), "i: %d", i)
 					if ts != nil {
 						require.Equal(t, exp[i].t, *ts, "i: %d", i)
@ -2000,11 +1998,11 @@ func TestProtobufParse(t *testing.T) {
 						require.Equal(t, exp[i].e[0], e, "i: %d", i)
 						require.False(t, p.Exemplar(&e), "too many exemplars returned, i: %d", i)
 					}
-					if exp[i].ct != nil {
-						require.True(t, ctFound, "i: %d", i)
-						require.Equal(t, exp[i].ct.String(), ct.String(), "i: %d", i)
+					if exp[i].ct != 0 {
+						require.NotNilf(t, ct, "i: %d", i)
+						require.Equal(t, exp[i].ct, *ct, "i: %d", i)
 					} else {
-						require.False(t, ctFound, "i: %d", i)
+						require.Nilf(t, ct, "i: %d", i)
 					}

 				case EntryHistogram:
--- a/scrape/helpers_test.go
+++ b/scrape/helpers_test.go
@ -14,10 +14,18 @@
 package scrape

 import (
+	"bytes"
 	"context"
+	"encoding/binary"
 	"fmt"
 	"math/rand"
 	"strings"
+	"sync"
+	"testing"
+
+	"github.com/gogo/protobuf/proto"
+	dto "github.com/prometheus/client_model/go"
+	"github.com/stretchr/testify/require"

 	"github.com/prometheus/prometheus/model/exemplar"
 	"github.com/prometheus/prometheus/model/histogram"
@ -50,6 +58,10 @@ func (a nopAppender) UpdateMetadata(storage.SeriesRef, labels.Labels, metadata.M
 	return 0, nil
 }

+func (a nopAppender) AppendCTZeroSample(storage.SeriesRef, labels.Labels, int64, int64) (storage.SeriesRef, error) {
+	return 0, nil
+}
+
 func (a nopAppender) Commit() error   { return nil }
 func (a nopAppender) Rollback() error { return nil }

@ -65,9 +77,19 @@ type histogramSample struct {
 	fh *histogram.FloatHistogram
 }

+type collectResultAppendable struct {
+	*collectResultAppender
+}
+
+func (a *collectResultAppendable) Appender(_ context.Context) storage.Appender {
+	return a
+}
+
 // collectResultAppender records all samples that were added through the appender.
 // It can be used as its zero value or be backed by another appender it writes samples through.
 type collectResultAppender struct {
+	mtx sync.Mutex
+
 	next                 storage.Appender
 	resultFloats         []floatSample
 	pendingFloats        []floatSample
@ -82,6 +104,8 @@ type collectResultAppender struct {
 }

 func (a *collectResultAppender) Append(ref storage.SeriesRef, lset labels.Labels, t int64, v float64) (storage.SeriesRef, error) {
+	a.mtx.Lock()
+	defer a.mtx.Unlock()
 	a.pendingFloats = append(a.pendingFloats, floatSample{
 		metric: lset,
 		t:      t,
@ -103,6 +127,8 @@ func (a *collectResultAppender) Append(ref storage.SeriesRef, lset labels.Labels
 }

 func (a *collectResultAppender) AppendExemplar(ref storage.SeriesRef, l labels.Labels, e exemplar.Exemplar) (storage.SeriesRef, error) {
+	a.mtx.Lock()
+	defer a.mtx.Unlock()
 	a.pendingExemplars = append(a.pendingExemplars, e)
 	if a.next == nil {
 		return 0, nil
@ -112,6 +138,8 @@ func (a *collectResultAppender) AppendExemplar(ref storage.SeriesRef, l labels.L
 }

 func (a *collectResultAppender) AppendHistogram(ref storage.SeriesRef, l labels.Labels, t int64, h *histogram.Histogram, fh *histogram.FloatHistogram) (storage.SeriesRef, error) {
+	a.mtx.Lock()
+	defer a.mtx.Unlock()
 	a.pendingHistograms = append(a.pendingHistograms, histogramSample{h: h, fh: fh, t: t})
 	if a.next == nil {
 		return 0, nil
@ -121,6 +149,8 @@ func (a *collectResultAppender) AppendHistogram(ref storage.SeriesRef, l labels.
 }

 func (a *collectResultAppender) UpdateMetadata(ref storage.SeriesRef, l labels.Labels, m metadata.Metadata) (storage.SeriesRef, error) {
+	a.mtx.Lock()
+	defer a.mtx.Unlock()
 	a.pendingMetadata = append(a.pendingMetadata, m)
 	if ref == 0 {
 		ref = storage.SeriesRef(rand.Uint64())
@ -132,7 +162,13 @@ func (a *collectResultAppender) UpdateMetadata(ref storage.SeriesRef, l labels.L
 	return a.next.UpdateMetadata(ref, l, m)
 }

+func (a *collectResultAppender) AppendCTZeroSample(ref storage.SeriesRef, l labels.Labels, t, ct int64) (storage.SeriesRef, error) {
+	return a.Append(ref, l, ct, 0.0)
+}
+
 func (a *collectResultAppender) Commit() error {
+	a.mtx.Lock()
+	defer a.mtx.Unlock()
 	a.resultFloats = append(a.resultFloats, a.pendingFloats...)
 	a.resultExemplars = append(a.resultExemplars, a.pendingExemplars...)
 	a.resultHistograms = append(a.resultHistograms, a.pendingHistograms...)
@ -148,6 +184,8 @@ func (a *collectResultAppender) Commit() error {
 }

 func (a *collectResultAppender) Rollback() error {
+	a.mtx.Lock()
+	defer a.mtx.Unlock()
 	a.rolledbackFloats = a.pendingFloats
 	a.rolledbackHistograms = a.pendingHistograms
 	a.pendingFloats = nil
@ -171,3 +209,22 @@ func (a *collectResultAppender) String() string {
 	}
 	return sb.String()
 }
+
+// protoMarshalDelimited marshals a MetricFamily into a delimited
+// Prometheus proto exposition format bytes (known as 'encoding=delimited`)
+//
+// See also https://eli.thegreenplace.net/2011/08/02/length-prefix-framing-for-protocol-buffers
+func protoMarshalDelimited(t *testing.T, mf *dto.MetricFamily) []byte {
+	t.Helper()
+
+	protoBuf, err := proto.Marshal(mf)
+	require.NoError(t, err)
+
+	varintBuf := make([]byte, binary.MaxVarintLen32)
+	varintLength := binary.PutUvarint(varintBuf, uint64(len(protoBuf)))
+
+	buf := &bytes.Buffer{}
+	buf.Write(varintBuf[:varintLength])
+	buf.Write(protoBuf)
+	return buf.Bytes()
+}
--- a/scrape/manager.go
+++ b/scrape/manager.go
@ -78,9 +78,15 @@ type Options struct {
 	EnableMetadataStorage bool
 	// Option to increase the interval used by scrape manager to throttle target groups updates.
 	DiscoveryReloadInterval model.Duration
+	// Option to enable the ingestion of the created timestamp as a synthetic zero sample.
+	// See: https://github.com/prometheus/proposals/blob/main/proposals/2023-06-13_created-timestamp.md
+	EnableCreatedTimestampZeroIngestion bool

 	// Optional HTTP client options to use when scraping.
 	HTTPClientOptions []config_util.HTTPClientOption
+
+	// private option for testability.
+	skipOffsetting bool
 }

 // Manager maintains a set of scrape pools and manages start/stop cycles
--- a/scrape/manager_test.go
+++ b/scrape/manager_test.go
@ -15,14 +15,23 @@ package scrape

 import (
 	"context"
+	"fmt"
 	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"os"
 	"strconv"
+	"sync"
 	"testing"
 	"time"

+	"github.com/go-kit/log"
+	"github.com/gogo/protobuf/proto"
 	"github.com/prometheus/client_golang/prometheus"
+	dto "github.com/prometheus/client_model/go"
 	"github.com/prometheus/common/model"
 	"github.com/stretchr/testify/require"
+	"google.golang.org/protobuf/types/known/timestamppb"
 	"gopkg.in/yaml.v2"

 	"github.com/prometheus/prometheus/config"
@ -30,6 +39,7 @@ import (
 	"github.com/prometheus/prometheus/discovery/targetgroup"
 	"github.com/prometheus/prometheus/model/labels"
 	"github.com/prometheus/prometheus/model/relabel"
+	"github.com/prometheus/prometheus/util/runutil"
 )

 func TestPopulateLabels(t *testing.T) {
@ -714,3 +724,146 @@ scrape_configs:
 	reload(scrapeManager, cfg2)
 	require.ElementsMatch(t, []string{"job1", "job3"}, scrapeManager.ScrapePools())
 }
+
+// TestManagerCTZeroIngestion tests scrape manager for CT cases.
+func TestManagerCTZeroIngestion(t *testing.T) {
+	const mName = "expected_counter"
+
+	for _, tc := range []struct {
+		name                  string
+		counterSample         *dto.Counter
+		enableCTZeroIngestion bool
+
+		expectedValues []float64
+	}{
+		{
+			name: "disabled with CT on counter",
+			counterSample: &dto.Counter{
+				Value: proto.Float64(1.0),
+				// Timestamp does not matter as long as it exists in this test.
+				CreatedTimestamp: timestamppb.Now(),
+			},
+			expectedValues: []float64{1.0},
+		},
+		{
+			name: "enabled with CT on counter",
+			counterSample: &dto.Counter{
+				Value: proto.Float64(1.0),
+				// Timestamp does not matter as long as it exists in this test.
+				CreatedTimestamp: timestamppb.Now(),
+			},
+			enableCTZeroIngestion: true,
+			expectedValues:        []float64{0.0, 1.0},
+		},
+		{
+			name: "enabled without CT on counter",
+			counterSample: &dto.Counter{
+				Value: proto.Float64(1.0),
+			},
+			enableCTZeroIngestion: true,
+			expectedValues:        []float64{1.0},
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			app := &collectResultAppender{}
+			scrapeManager, err := NewManager(
+				&Options{
+					EnableCreatedTimestampZeroIngestion: tc.enableCTZeroIngestion,
+					skipOffsetting:                      true,
+				},
+				log.NewLogfmtLogger(os.Stderr),
+				&collectResultAppendable{app},
+				prometheus.NewRegistry(),
+			)
+			require.NoError(t, err)
+
+			require.NoError(t, scrapeManager.ApplyConfig(&config.Config{
+				GlobalConfig: config.GlobalConfig{
+					// Disable regular scrapes.
+					ScrapeInterval: model.Duration(9999 * time.Minute),
+					ScrapeTimeout:  model.Duration(5 * time.Second),
+					// Ensure the proto is chosen. We need proto as it's the only protocol
+					// with the CT parsing support.
+					ScrapeProtocols: []config.ScrapeProtocol{config.PrometheusProto},
+				},
+				ScrapeConfigs: []*config.ScrapeConfig{{JobName: "test"}},
+			}))
+
+			once := sync.Once{}
+			// Start fake HTTP target to that allow one scrape only.
+			server := httptest.NewServer(
+				http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+					fail := true
+					once.Do(func() {
+						fail = false
+						w.Header().Set("Content-Type", `application/vnd.google.protobuf; proto=io.prometheus.client.MetricFamily; encoding=delimited`)
+
+						ctrType := dto.MetricType_COUNTER
+						w.Write(protoMarshalDelimited(t, &dto.MetricFamily{
+							Name:   proto.String(mName),
+							Type:   &ctrType,
+							Metric: []*dto.Metric{{Counter: tc.counterSample}},
+						}))
+					})
+
+					if fail {
+						w.WriteHeader(http.StatusInternalServerError)
+					}
+				}),
+			)
+			defer server.Close()
+
+			serverURL, err := url.Parse(server.URL)
+			require.NoError(t, err)
+
+			// Add fake target directly into tsets + reload. Normally users would use
+			// Manager.Run and wait for minimum 5s refresh interval.
+			scrapeManager.updateTsets(map[string][]*targetgroup.Group{
+				"test": {{
+					Targets: []model.LabelSet{{
+						model.SchemeLabel:  model.LabelValue(serverURL.Scheme),
+						model.AddressLabel: model.LabelValue(serverURL.Host),
+					}},
+				}},
+			})
+			scrapeManager.reload()
+
+			// Wait for one scrape.
+			ctx, cancel := context.WithTimeout(context.Background(), 1*time.Minute)
+			defer cancel()
+			require.NoError(t, runutil.Retry(100*time.Millisecond, ctx.Done(), func() error {
+				if countFloatSamples(app, mName) != len(tc.expectedValues) {
+					return fmt.Errorf("expected %v samples", tc.expectedValues)
+				}
+				return nil
+			}), "after 1 minute")
+			scrapeManager.Stop()
+
+			require.Equal(t, tc.expectedValues, getResultFloats(app, mName))
+		})
+	}
+}
+
+func countFloatSamples(a *collectResultAppender, expectedMetricName string) (count int) {
+	a.mtx.Lock()
+	defer a.mtx.Unlock()
+
+	for _, f := range a.resultFloats {
+		if f.metric.Get(model.MetricNameLabel) == expectedMetricName {
+			count++
+		}
+	}
+	return count
+}
+
+func getResultFloats(app *collectResultAppender, expectedMetricName string) (result []float64) {
+	app.mtx.Lock()
+	defer app.mtx.Unlock()
+
+	for _, f := range app.resultFloats {
+		if f.metric.Get(model.MetricNameLabel) == expectedMetricName {
+			result = append(result, f.f)
+		}
+	}
+	return result
+}
--- a/scrape/scrape.go
+++ b/scrape/scrape.go
@ -106,9 +106,10 @@ type scrapeLoopOptions struct {
 	interval                 time.Duration
 	timeout                  time.Duration
 	scrapeClassicHistograms  bool
-	mrc                      []*relabel.Config
-	cache                    *scrapeCache
-	enableCompression        bool
+
+	mrc               []*relabel.Config
+	cache             *scrapeCache
+	enableCompression bool
 }

 const maxAheadTime = 10 * time.Minute
@ -168,11 +169,13 @@ func newScrapePool(cfg *config.ScrapeConfig, app storage.Appendable, offsetSeed
 			opts.interval,
 			opts.timeout,
 			opts.scrapeClassicHistograms,
+			options.EnableCreatedTimestampZeroIngestion,
 			options.ExtraMetrics,
 			options.EnableMetadataStorage,
 			opts.target,
 			options.PassMetadataInContext,
 			metrics,
+			options.skipOffsetting,
 		)
 	}
 	sp.metrics.targetScrapePoolTargetLimit.WithLabelValues(sp.config.JobName).Set(float64(sp.config.TargetLimit))
@ -787,6 +790,7 @@ type scrapeLoop struct {
 	interval                 time.Duration
 	timeout                  time.Duration
 	scrapeClassicHistograms  bool
+	enableCTZeroIngestion    bool

 	appender            func(ctx context.Context) storage.Appender
 	sampleMutator       labelsMutator
@ -804,6 +808,8 @@ type scrapeLoop struct {
 	appendMetadataToWAL bool

 	metrics *scrapeMetrics
+
+	skipOffsetting bool // For testability.
 }

 // scrapeCache tracks mappings of exposed metric strings to label sets and
@ -1076,11 +1082,13 @@ func newScrapeLoop(ctx context.Context,
 	interval time.Duration,
 	timeout time.Duration,
 	scrapeClassicHistograms bool,
+	enableCTZeroIngestion bool,
 	reportExtraMetrics bool,
 	appendMetadataToWAL bool,
 	target *Target,
 	passMetadataInContext bool,
 	metrics *scrapeMetrics,
+	skipOffsetting bool,
 ) *scrapeLoop {
 	if l == nil {
 		l = log.NewNopLogger()
@ -1124,9 +1132,11 @@ func newScrapeLoop(ctx context.Context,
 		interval:                 interval,
 		timeout:                  timeout,
 		scrapeClassicHistograms:  scrapeClassicHistograms,
+		enableCTZeroIngestion:    enableCTZeroIngestion,
 		reportExtraMetrics:       reportExtraMetrics,
 		appendMetadataToWAL:      appendMetadataToWAL,
 		metrics:                  metrics,
+		skipOffsetting:           skipOffsetting,
 	}
 	sl.ctx, sl.cancel = context.WithCancel(ctx)

@ -1134,12 +1144,14 @@ func newScrapeLoop(ctx context.Context,
 }

 func (sl *scrapeLoop) run(errc chan<- error) {
-	select {
-	case <-time.After(sl.scraper.offset(sl.interval, sl.offsetSeed)):
-		// Continue after a scraping offset.
-	case <-sl.ctx.Done():
-		close(sl.stopped)
-		return
+	if !sl.skipOffsetting {
+		select {
+		case <-time.After(sl.scraper.offset(sl.interval, sl.offsetSeed)):
+			// Continue after a scraping offset.
+		case <-sl.ctx.Done():
+			close(sl.stopped)
+			return
+		}
 	}

 	var last time.Time
@ -1557,6 +1569,15 @@ loop:
 			updateMetadata(lset, true)
 		}

+		if ctMs := p.CreatedTimestamp(); sl.enableCTZeroIngestion && ctMs != nil {
+			ref, err = app.AppendCTZeroSample(ref, lset, t, *ctMs)
+			if err != nil && !errors.Is(err, storage.ErrOutOfOrderCT) { // OOO is a common case, ignoring completely for now.
+				// CT is an experimental feature. For now, we don't need to fail the
+				// scrape on errors updating the created timestamp, log debug.
+				level.Debug(sl.l).Log("msg", "Error when appending CT in scrape loop", "series", string(met), "ct", *ctMs, "t", t, "err", err)
+			}
+		}
+
 		if isHistogram {
 			if h != nil {
 				ref, err = app.AppendHistogram(ref, lset, t, h, nil)
--- a/scrape/scrape_test.go
+++ b/scrape/scrape_test.go
@ -660,9 +660,11 @@ func newBasicScrapeLoop(t testing.TB, ctx context.Context, scraper scraper, app
 		false,
 		false,
 		false,
+		false,
 		nil,
 		false,
 		newTestScrapeMetrics(t),
+		false,
 	)
 }

@ -801,9 +803,11 @@ func TestScrapeLoopRun(t *testing.T) {
 		false,
 		false,
 		false,
+		false,
 		nil,
 		false,
 		scrapeMetrics,
+		false,
 	)

 	// The loop must terminate during the initial offset if the context
@ -945,9 +949,11 @@ func TestScrapeLoopMetadata(t *testing.T) {
 		false,
 		false,
 		false,
+		false,
 		nil,
 		false,
 		scrapeMetrics,
+		false,
 	)
 	defer cancel()

@ -2377,7 +2383,7 @@ func TestTargetScraperScrapeOK(t *testing.T) {

 	runTest(acceptHeader(config.DefaultScrapeProtocols))
 	protobufParsing = true
-	runTest(acceptHeader(config.DefaultNativeHistogramScrapeProtocols))
+	runTest(acceptHeader(config.DefaultProtoFirstScrapeProtocols))
 }

 func TestTargetScrapeScrapeCancel(t *testing.T) {
--- a/storage/fanout.go
+++ b/storage/fanout.go
@ -202,6 +202,20 @@ func (f *fanoutAppender) UpdateMetadata(ref SeriesRef, l labels.Labels, m metada
 	return ref, nil
 }

+func (f *fanoutAppender) AppendCTZeroSample(ref SeriesRef, l labels.Labels, t, ct int64) (SeriesRef, error) {
+	ref, err := f.primary.AppendCTZeroSample(ref, l, t, ct)
+	if err != nil {
+		return ref, err
+	}
+
+	for _, appender := range f.secondaries {
+		if _, err := appender.AppendCTZeroSample(ref, l, t, ct); err != nil {
+			return 0, err
+		}
+	}
+	return ref, nil
+}
+
 func (f *fanoutAppender) Commit() (err error) {
 	err = f.primary.Commit()

--- a/storage/interface.go
+++ b/storage/interface.go
@ -43,6 +43,13 @@ var (
 	ErrExemplarLabelLength         = fmt.Errorf("label length for exemplar exceeds maximum of %d UTF-8 characters", exemplar.ExemplarMaxLabelSetLength)
 	ErrExemplarsDisabled           = fmt.Errorf("exemplar storage is disabled or max exemplars is less than or equal to 0")
 	ErrNativeHistogramsDisabled    = fmt.Errorf("native histograms are disabled")
+
+	// ErrOutOfOrderCT indicates failed append of CT to the storage
+	// due to CT being older the then newer sample.
+	// NOTE(bwplotka): This can be both an instrumentation failure or commonly expected
+	// behaviour, and we currently don't have a way to determine this. As a result
+	// it's recommended to ignore this error for now.
+	ErrOutOfOrderCT = fmt.Errorf("created timestamp out of order, ignoring")
 )

 // SeriesRef is a generic series reference. In prometheus it is either a
@ -237,6 +244,7 @@ type Appender interface {
 	ExemplarAppender
 	HistogramAppender
 	MetadataUpdater
+	CreatedTimestampAppender
 }

 // GetRef is an extra interface on Appenders used by downstream projects
@ -294,6 +302,24 @@ type MetadataUpdater interface {
 	UpdateMetadata(ref SeriesRef, l labels.Labels, m metadata.Metadata) (SeriesRef, error)
 }

+// CreatedTimestampAppender provides an interface for appending CT to storage.
+type CreatedTimestampAppender interface {
+	// AppendCTZeroSample adds synthetic zero sample for the given ct timestamp,
+	// which will be associated with given series, labels and the incoming
+	// sample's t (timestamp). AppendCTZeroSample returns error if zero sample can't be
+	// appended, for example when ct is too old, or when it would collide with
+	// incoming sample (sample has priority).
+	//
+	// AppendCTZeroSample has to be called before the corresponding sample Append.
+	// A series reference number is returned which can be used to modify the
+	// CT for the given series in the same or later transactions.
+	// Returned reference numbers are ephemeral and may be rejected in calls
+	// to AppendCTZeroSample() at any point.
+	//
+	// If the reference is 0 it must not be used for caching.
+	AppendCTZeroSample(ref SeriesRef, l labels.Labels, t, ct int64) (SeriesRef, error)
+}
+
 // SeriesSet contains a set of series.
 type SeriesSet interface {
 	Next() bool
--- a/storage/remote/write.go
+++ b/storage/remote/write.go
@ -303,6 +303,11 @@ func (t *timestampTracker) UpdateMetadata(_ storage.SeriesRef, _ labels.Labels,
 	return 0, nil
 }

+func (t *timestampTracker) AppendCTZeroSample(_ storage.SeriesRef, _ labels.Labels, _, _ int64) (storage.SeriesRef, error) {
+	// AppendCTZeroSample is no-op for remote-write for now.
+	return 0, nil
+}
+
 // Commit implements storage.Appender.
 func (t *timestampTracker) Commit() error {
 	t.writeStorage.samplesIn.incr(t.samples + t.exemplars + t.histograms)
--- a/storage/remote/write_handler_test.go
+++ b/storage/remote/write_handler_test.go
@ -339,3 +339,8 @@ func (m *mockAppendable) UpdateMetadata(_ storage.SeriesRef, _ labels.Labels, _
 	// UpdateMetadata is no-op for remote write (where mockAppendable is being used to test) for now.
 	return 0, nil
 }
+
+func (m *mockAppendable) AppendCTZeroSample(_ storage.SeriesRef, _ labels.Labels, _, _ int64) (storage.SeriesRef, error) {
+	// AppendCTZeroSample is no-op for remote-write for now.
+	return 0, nil
+}
--- a/tsdb/agent/db.go
+++ b/tsdb/agent/db.go
@ -962,6 +962,11 @@ func (a *appender) UpdateMetadata(storage.SeriesRef, labels.Labels, metadata.Met
 	return 0, nil
 }

+func (a *appender) AppendCTZeroSample(storage.SeriesRef, labels.Labels, int64, int64) (storage.SeriesRef, error) {
+	// TODO(bwplotka): Wire metadata in the Agent's appender.
+	return 0, nil
+}
+
 // Commit submits the collected samples and purges the batch.
 func (a *appender) Commit() error {
 	if err := a.log(); err != nil {
--- a/tsdb/head.go
+++ b/tsdb/head.go
@ -149,6 +149,10 @@ type HeadOptions struct {
 	// EnableNativeHistograms enables the ingestion of native histograms.
 	EnableNativeHistograms atomic.Bool

+	// EnableCreatedTimestampZeroIngestion enables the ingestion of the created timestamp as a synthetic zero sample.
+	// See: https://github.com/prometheus/proposals/blob/main/proposals/2023-06-13_created-timestamp.md
+	EnableCreatedTimestampZeroIngestion bool
+
 	ChunkRange int64
 	// ChunkDirRoot is the parent directory of the chunks directory.
 	ChunkDirRoot         string
--- a/tsdb/head_append.go
+++ b/tsdb/head_append.go
@ -87,6 +87,17 @@ func (a *initAppender) UpdateMetadata(ref storage.SeriesRef, l labels.Labels, m
 	return a.app.UpdateMetadata(ref, l, m)
 }

+func (a *initAppender) AppendCTZeroSample(ref storage.SeriesRef, lset labels.Labels, t, ct int64) (storage.SeriesRef, error) {
+	if a.app != nil {
+		return a.app.AppendCTZeroSample(ref, lset, t, ct)
+	}
+
+	a.head.initTime(t)
+	a.app = a.head.appender()
+
+	return a.app.AppendCTZeroSample(ref, lset, t, ct)
+}
+
 // initTime initializes a head with the first timestamp. This only needs to be called
 // for a completely fresh head with an empty WAL.
 func (h *Head) initTime(t int64) {
@ -319,28 +330,11 @@ func (a *headAppender) Append(ref storage.SeriesRef, lset labels.Labels, t int64

 	s := a.head.series.getByID(chunks.HeadSeriesRef(ref))
 	if s == nil {
-		// Ensure no empty labels have gotten through.
-		lset = lset.WithoutEmpty()
-		if lset.IsEmpty() {
-			return 0, errors.Wrap(ErrInvalidSample, "empty labelset")
-		}
-
-		if l, dup := lset.HasDuplicateLabelNames(); dup {
-			return 0, errors.Wrap(ErrInvalidSample, fmt.Sprintf(`label name "%s" is not unique`, l))
-		}
-
-		var created bool
 		var err error
-		s, created, err = a.head.getOrCreate(lset.Hash(), lset)
+		s, err = a.getOrCreate(lset)
 		if err != nil {
 			return 0, err
 		}
-		if created {
-			a.series = append(a.series, record.RefSeries{
-				Ref:    s.ref,
-				Labels: lset,
-			})
-		}
 	}

 	if value.IsStaleNaN(v) {
@ -389,6 +383,71 @@ func (a *headAppender) Append(ref storage.SeriesRef, lset labels.Labels, t int64
 	return storage.SeriesRef(s.ref), nil
 }

+// AppendCTZeroSample appends synthetic zero sample for ct timestamp. It returns
+// error when sample can't be appended. See
+// storage.CreatedTimestampAppender.AppendCTZeroSample for further documentation.
+func (a *headAppender) AppendCTZeroSample(ref storage.SeriesRef, lset labels.Labels, t, ct int64) (storage.SeriesRef, error) {
+	if ct >= t {
+		return 0, fmt.Errorf("CT is newer or the same as sample's timestamp, ignoring")
+	}
+
+	s := a.head.series.getByID(chunks.HeadSeriesRef(ref))
+	if s == nil {
+		var err error
+		s, err = a.getOrCreate(lset)
+		if err != nil {
+			return 0, err
+		}
+	}
+
+	// Check if CT wouldn't be OOO vs samples we already might have for this series.
+	// NOTE(bwplotka): This will be often hit as it's expected for long living
+	// counters to share the same CT.
+	s.Lock()
+	isOOO, _, err := s.appendable(ct, 0, a.headMaxt, a.minValidTime, a.oooTimeWindow)
+	if err == nil {
+		s.pendingCommit = true
+	}
+	s.Unlock()
+	if err != nil {
+		return 0, err
+	}
+	if isOOO {
+		return storage.SeriesRef(s.ref), storage.ErrOutOfOrderCT
+	}
+
+	if ct > a.maxt {
+		a.maxt = ct
+	}
+	a.samples = append(a.samples, record.RefSample{Ref: s.ref, T: ct, V: 0.0})
+	a.sampleSeries = append(a.sampleSeries, s)
+	return storage.SeriesRef(s.ref), nil
+}
+
+func (a *headAppender) getOrCreate(lset labels.Labels) (*memSeries, error) {
+	// Ensure no empty labels have gotten through.
+	lset = lset.WithoutEmpty()
+	if lset.IsEmpty() {
+		return nil, errors.Wrap(ErrInvalidSample, "empty labelset")
+	}
+	if l, dup := lset.HasDuplicateLabelNames(); dup {
+		return nil, errors.Wrap(ErrInvalidSample, fmt.Sprintf(`label name "%s" is not unique`, l))
+	}
+	var created bool
+	var err error
+	s, created, err := a.head.getOrCreate(lset.Hash(), lset)
+	if err != nil {
+		return nil, err
+	}
+	if created {
+		a.series = append(a.series, record.RefSeries{
+			Ref:    s.ref,
+			Labels: lset,
+		})
+	}
+	return s, nil
+}
+
 // appendable checks whether the given sample is valid for appending to the series. (if we return false and no error)
 // The sample belongs to the out of order chunk if we return true and no error.
 // An error signifies the sample cannot be handled.
--- a/tsdb/head_test.go
+++ b/tsdb/head_test.go
@ -33,6 +33,7 @@ import (
 	"github.com/pkg/errors"
 	"github.com/prometheus/client_golang/prometheus"
 	prom_testutil "github.com/prometheus/client_golang/prometheus/testutil"
+	"github.com/prometheus/common/model"
 	"github.com/stretchr/testify/require"
 	"go.uber.org/atomic"
 	"golang.org/x/sync/errgroup"
@ -5641,3 +5642,93 @@ func TestPostingsCardinalityStats(t *testing.T) {
 	// Using cache.
 	require.Equal(t, statsForSomeLabel1, head.PostingsCardinalityStats("n", 1))
 }
+
+func TestHeadAppender_AppendCTZeroSample(t *testing.T) {
+	type appendableSamples struct {
+		ts  int64
+		val float64
+		ct  int64
+	}
+	for _, tc := range []struct {
+		name              string
+		appendableSamples []appendableSamples
+		expectedSamples   []model.Sample
+	}{
+		{
+			name: "In order ct+normal sample",
+			appendableSamples: []appendableSamples{
+				{ts: 100, val: 10, ct: 1},
+			},
+			expectedSamples: []model.Sample{
+				{Timestamp: 1, Value: 0},
+				{Timestamp: 100, Value: 10},
+			},
+		},
+		{
+			name: "Consecutive appends with same ct ignore ct",
+			appendableSamples: []appendableSamples{
+				{ts: 100, val: 10, ct: 1},
+				{ts: 101, val: 10, ct: 1},
+			},
+			expectedSamples: []model.Sample{
+				{Timestamp: 1, Value: 0},
+				{Timestamp: 100, Value: 10},
+				{Timestamp: 101, Value: 10},
+			},
+		},
+		{
+			name: "Consecutive appends with newer ct do not ignore ct",
+			appendableSamples: []appendableSamples{
+				{ts: 100, val: 10, ct: 1},
+				{ts: 102, val: 10, ct: 101},
+			},
+			expectedSamples: []model.Sample{
+				{Timestamp: 1, Value: 0},
+				{Timestamp: 100, Value: 10},
+				{Timestamp: 101, Value: 0},
+				{Timestamp: 102, Value: 10},
+			},
+		},
+		{
+			name: "CT equals to previous sample timestamp is ignored",
+			appendableSamples: []appendableSamples{
+				{ts: 100, val: 10, ct: 1},
+				{ts: 101, val: 10, ct: 100},
+			},
+			expectedSamples: []model.Sample{
+				{Timestamp: 1, Value: 0},
+				{Timestamp: 100, Value: 10},
+				{Timestamp: 101, Value: 10},
+			},
+		},
+	} {
+		h, _ := newTestHead(t, DefaultBlockDuration, wlog.CompressionNone, false)
+		defer func() {
+			require.NoError(t, h.Close())
+		}()
+		a := h.Appender(context.Background())
+		lbls := labels.FromStrings("foo", "bar")
+		for _, sample := range tc.appendableSamples {
+			_, err := a.AppendCTZeroSample(0, lbls, sample.ts, sample.ct)
+			require.NoError(t, err)
+			_, err = a.Append(0, lbls, sample.ts, sample.val)
+			require.NoError(t, err)
+		}
+		require.NoError(t, a.Commit())
+
+		q, err := NewBlockQuerier(h, math.MinInt64, math.MaxInt64)
+		require.NoError(t, err)
+		ss := q.Select(context.Background(), false, nil, labels.MustNewMatcher(labels.MatchEqual, "foo", "bar"))
+		require.True(t, ss.Next())
+		s := ss.At()
+		require.False(t, ss.Next())
+		it := s.Iterator(nil)
+		for _, sample := range tc.expectedSamples {
+			require.Equal(t, chunkenc.ValFloat, it.Next())
+			timestamp, value := it.At()
+			require.Equal(t, sample.Timestamp, model.Time(timestamp))
+			require.Equal(t, sample.Value, model.SampleValue(value))
+		}
+		require.Equal(t, chunkenc.ValNone, it.Next())
+	}
+}
--- a/util/runutil/runutil.go
+++ b/util/runutil/runutil.go
@ -0,0 +1,37 @@
+// Copyright 2013 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Copied from https://github.com/efficientgo/core/blob/a21078e2c723b69e05f95c65dbc5058712b4edd8/runutil/runutil.go#L39
+// and adjusted.
+
+package runutil
+
+import "time"
+
+// Retry executes f every interval seconds until timeout or no error is returned from f.
+func Retry(interval time.Duration, stopc <-chan struct{}, f func() error) error {
+	tick := time.NewTicker(interval)
+	defer tick.Stop()
+
+	var err error
+	for {
+		if err = f(); err == nil {
+			return nil
+		}
+		select {
+		case <-stopc:
+			return err
+		case <-tick.C:
+		}
+	}
+}