feat: Append created timestamp as metadata

Signed-off-by: Arthur Silva Sens <arthursens2005@gmail.com>

model/metadata/metadata.go

@@ -17,7 +17,8 @@ import "github.com/prometheus/common/model"
 
 // Metadata stores a series' metadata information.
 type Metadata struct {
-	Type model.MetricType `json:"type"`
-	Unit string           `json:"unit"`
-	Help string           `json:"help"`
+	Type             model.MetricType `json:"type"`
+	Unit             string           `json:"unit"`
+	Help             string           `json:"help"`
+	CreatedTimestamp int64            `json:"created_timestamp"`
 }

scrape/scrape.go

@@ -1080,6 +1080,23 @@ func (c *scrapeCache) setUnit(metric, unit []byte) {
 	c.metaMtx.Unlock()
 }
 
+func (c *scrapeCache) setCreatedTimestamp(metric []byte, ct int64) {
+	c.metaMtx.Lock()
+
+	e, ok := c.metadata[string(metric)]
+	if !ok {
+		e = &metaEntry{Metadata: metadata.Metadata{Type: model.MetricTypeUnknown}}
+		c.metadata[string(metric)] = e
+	}
+	if e.CreatedTimestamp != ct {
+		e.CreatedTimestamp = ct
+		e.lastIterChange = c.iter
+	}
+	e.lastIter = c.iter
+
+	c.metaMtx.Unlock()
+}
+
 func (c *scrapeCache) GetMetadata(metric string) (MetricMetadata, bool) {
 	c.metaMtx.Lock()
 	defer c.metaMtx.Unlock()
@@ -1089,10 +1106,11 @@ func (c *scrapeCache) GetMetadata(metric string) (MetricMetadata, bool) {
 		return MetricMetadata{}, false
 	}
 	return MetricMetadata{
-		Metric: metric,
-		Type:   m.Type,
-		Help:   m.Help,
-		Unit:   m.Unit,
+		Metric:           metric,
+		Type:             m.Type,
+		Help:             m.Help,
+		Unit:             m.Unit,
+		CreatedTimestamp: m.CreatedTimestamp,
 	}, true
 }
 
@@ -1104,10 +1122,11 @@ func (c *scrapeCache) ListMetadata() []MetricMetadata {
 
 	for m, e := range c.metadata {
 		res = append(res, MetricMetadata{
-			Metric: m,
-			Type:   e.Type,
-			Help:   e.Help,
-			Unit:   e.Unit,
+			Metric:           m,
+			Type:             e.Type,
+			Help:             e.Help,
+			Unit:             e.Unit,
+			CreatedTimestamp: e.CreatedTimestamp,
 		})
 	}
 	return res
@@ -1528,6 +1547,7 @@ func (sl *scrapeLoop) append(app storage.Appender, b []byte, contentType string,
 			meta.Type = metaEntry.Type
 			meta.Unit = metaEntry.Unit
 			meta.Help = metaEntry.Help
+			meta.CreatedTimestamp = metaEntry.CreatedTimestamp
 			return true
 		}
 		return false
@@ -1610,9 +1630,6 @@ loop:
 			ref = ce.ref
 			lset = ce.lset
 			hash = ce.hash
-
-			// Update metadata only if it changed in the current iteration.
-			updateMetadata(lset, false)
 		} else {
 			p.Metric(&lset)
 			hash = lset.Hash()
@@ -1641,15 +1658,13 @@ loop:
 				sl.metrics.targetScrapePoolExceededLabelLimits.Inc()
 				break loop
 			}
-
-			// Append metadata for new series if they were present.
-			updateMetadata(lset, true)
 		}
 
 		if seriesAlreadyScraped {
 			err = storage.ErrDuplicateSampleForTimestamp
 		} else {
-			if ctMs := p.CreatedTimestamp(); sl.enableCTZeroIngestion && ctMs != nil {
+			ctMs := p.CreatedTimestamp()
+			if 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
@@ -1657,6 +1672,9 @@ loop:
 					level.Debug(sl.l).Log("msg", "Error when appending CT in scrape loop", "series", string(met), "ct", *ctMs, "t", t, "err", err)
 				}
 			}
+			if ctMs != nil {
+				sl.cache.setCreatedTimestamp(met, *ctMs)
+			}
 
 			if isHistogram && sl.enableNativeHistogramIngestion {
 				if h != nil {
@@ -1669,6 +1687,10 @@ loop:
 			}
 		}
 
+		// If they were present, append metadata for new series
+		// or for existing series if the metadata has changed.
+		updateMetadata(lset, !ok)
+
 		if err == nil {
 			if (parsedTimestamp == nil || sl.trackTimestampsStaleness) && ce != nil {
 				sl.cache.trackStaleness(ce.hash, ce.lset)

scrape/scrape_test.go

@@ -962,7 +962,7 @@ func TestScrapeLoopMetadata(t *testing.T) {
 		0,
 		false,
 		false,
-		false,
+		true, // EnableCTZeroIngestion
 		false,
 		false,
 		nil,
@@ -977,30 +977,36 @@ func TestScrapeLoopMetadata(t *testing.T) {
 # HELP test_metric some help text
 # UNIT test_metric metric
 test_metric 1
+test_metric_created 1000
 # TYPE test_metric_no_help gauge
 # HELP test_metric_no_type other help text
 # EOF`), "application/openmetrics-text", time.Now())
 	require.NoError(t, err)
 	require.NoError(t, slApp.Commit())
-	require.Equal(t, 1, total)
+	// It returns 2 below because _created lines are still being ingested as a metric when using OpenMetrics.
+	// TODO: _created lines should be ingested as metadata only, and not as a metric.
+	require.Equal(t, 2, total)
 
 	md, ok := cache.GetMetadata("test_metric")
 	require.True(t, ok, "expected metadata to be present")
 	require.Equal(t, model.MetricTypeCounter, md.Type, "unexpected metric type")
 	require.Equal(t, "some help text", md.Help)
 	require.Equal(t, "metric", md.Unit)
+	require.Equal(t, int64(1000), md.CreatedTimestamp)
 
 	md, ok = cache.GetMetadata("test_metric_no_help")
 	require.True(t, ok, "expected metadata to be present")
 	require.Equal(t, model.MetricTypeGauge, md.Type, "unexpected metric type")
 	require.Equal(t, "", md.Help)
 	require.Equal(t, "", md.Unit)
+	require.Equal(t, int64(0), md.CreatedTimestamp)
 
 	md, ok = cache.GetMetadata("test_metric_no_type")
 	require.True(t, ok, "expected metadata to be present")
 	require.Equal(t, model.MetricTypeUnknown, md.Type, "unexpected metric type")
 	require.Equal(t, "other help text", md.Help)
 	require.Equal(t, "", md.Unit)
+	require.Equal(t, int64(0), md.CreatedTimestamp)
 }
 
 func simpleTestScrapeLoop(t testing.TB) (context.Context, *scrapeLoop) {

scrape/target.go

@@ -85,10 +85,11 @@ type MetricMetadataStore interface {
 
 // MetricMetadata is a piece of metadata for a metric.
 type MetricMetadata struct {
-	Metric string
-	Type   model.MetricType
-	Help   string
-	Unit   string
+	Metric           string
+	Type             model.MetricType
+	Help             string
+	Unit             string
+	CreatedTimestamp int64
 }
 
 func (t *Target) ListMetadata() []MetricMetadata {

tsdb/db_test.go

@@ -4268,9 +4268,9 @@ func TestMetadataInWAL(t *testing.T) {
 
 	// Add a first round of metadata to the first three series.
 	// Re-take the Appender, as the previous Commit will have it closed.
-	m1 := metadata.Metadata{Type: "gauge", Unit: "unit_1", Help: "help_1"}
-	m2 := metadata.Metadata{Type: "gauge", Unit: "unit_2", Help: "help_2"}
-	m3 := metadata.Metadata{Type: "gauge", Unit: "unit_3", Help: "help_3"}
+	m1 := metadata.Metadata{Type: "gauge", Unit: "unit_1", Help: "help_1", CreatedTimestamp: 1234}
+	m2 := metadata.Metadata{Type: "gauge", Unit: "unit_2", Help: "help_2", CreatedTimestamp: 1000}
+	m3 := metadata.Metadata{Type: "gauge", Unit: "unit_3", Help: "help_3"} // Last one without Created Timestamp.
 	app = db.Appender(ctx)
 	updateMetadata(t, app, s1, m1)
 	updateMetadata(t, app, s2, m2)
@@ -4280,8 +4280,8 @@ func TestMetadataInWAL(t *testing.T) {
 	// Add a replicated metadata entry to the first series,
 	// a completely new metadata entry for the fourth series,
 	// and a changed metadata entry to the second series.
-	m4 := metadata.Metadata{Type: "counter", Unit: "unit_4", Help: "help_4"}
-	m5 := metadata.Metadata{Type: "counter", Unit: "unit_5", Help: "help_5"}
+	m4 := metadata.Metadata{Type: "counter", Unit: "unit_4", Help: "help_4", CreatedTimestamp: 2000}
+	m5 := metadata.Metadata{Type: "counter", Unit: "unit_5", Help: "help_5", CreatedTimestamp: 3000}
 	app = db.Appender(ctx)
 	updateMetadata(t, app, s1, m1)
 	updateMetadata(t, app, s4, m4)
@@ -4298,11 +4298,11 @@ func TestMetadataInWAL(t *testing.T) {
 	}
 
 	expectedMetadata := []record.RefMetadata{
-		{Ref: 1, Type: record.GetMetricType(m1.Type), Unit: m1.Unit, Help: m1.Help},
-		{Ref: 2, Type: record.GetMetricType(m2.Type), Unit: m2.Unit, Help: m2.Help},
-		{Ref: 3, Type: record.GetMetricType(m3.Type), Unit: m3.Unit, Help: m3.Help},
-		{Ref: 4, Type: record.GetMetricType(m4.Type), Unit: m4.Unit, Help: m4.Help},
-		{Ref: 2, Type: record.GetMetricType(m5.Type), Unit: m5.Unit, Help: m5.Help},
+		{Ref: 1, Type: record.GetMetricType(m1.Type), Unit: m1.Unit, Help: m1.Help, CreatedTimestamp: m1.CreatedTimestamp},
+		{Ref: 2, Type: record.GetMetricType(m2.Type), Unit: m2.Unit, Help: m2.Help, CreatedTimestamp: m2.CreatedTimestamp},
+		{Ref: 3, Type: record.GetMetricType(m3.Type), Unit: m3.Unit, Help: m3.Help, CreatedTimestamp: 0},
+		{Ref: 4, Type: record.GetMetricType(m4.Type), Unit: m4.Unit, Help: m4.Help, CreatedTimestamp: m4.CreatedTimestamp},
+		{Ref: 2, Type: record.GetMetricType(m5.Type), Unit: m5.Unit, Help: m5.Help, CreatedTimestamp: m5.CreatedTimestamp},
 	}
 	require.Len(t, gotMetadataBlocks, 2)
 	require.Equal(t, expectedMetadata[:3], gotMetadataBlocks[0])

tsdb/head_append.go

@@ -693,10 +693,11 @@ func (a *headAppender) UpdateMetadata(ref storage.SeriesRef, lset labels.Labels,
 
 	if hasNewMetadata {
 		a.metadata = append(a.metadata, record.RefMetadata{
-			Ref:  s.ref,
-			Type: record.GetMetricType(meta.Type),
-			Unit: meta.Unit,
-			Help: meta.Help,
+			Ref:              s.ref,
+			Type:             record.GetMetricType(meta.Type),
+			Unit:             meta.Unit,
+			Help:             meta.Help,
+			CreatedTimestamp: meta.CreatedTimestamp,
 		})
 		a.metadataSeries = append(a.metadataSeries, s)
 	}
@@ -1056,7 +1057,7 @@ func (a *headAppender) Commit() (err error) {
 	for i, m := range a.metadata {
 		series = a.metadataSeries[i]
 		series.Lock()
-		series.meta = &metadata.Metadata{Type: record.ToMetricType(m.Type), Unit: m.Unit, Help: m.Help}
+		series.meta = &metadata.Metadata{Type: record.ToMetricType(m.Type), Unit: m.Unit, Help: m.Help, CreatedTimestamp: m.CreatedTimestamp}
 		series.Unlock()
 	}
 

tsdb/record/record.go

@@ -134,8 +134,9 @@ func ToMetricType(m uint8) model.MetricType {
 }
 
 const (
-	unitMetaName = "UNIT"
-	helpMetaName = "HELP"
+	unitMetaName         = "UNIT"
+	helpMetaName         = "HELP"
+	createdTimestampName = "CREATED_TIMESTAMP"
 )
 
 // ErrNotFound is returned if a looked up resource was not found. Duplicate ErrNotFound from head.go.
@@ -157,10 +158,11 @@ type RefSample struct {
 
 // RefMetadata is the metadata associated with a series ID.
 type RefMetadata struct {
-	Ref  chunks.HeadSeriesRef
-	Type uint8
-	Unit string
-	Help string
+	Ref              chunks.HeadSeriesRef
+	Type             uint8
+	Unit             string
+	Help             string
+	CreatedTimestamp int64
 }
 
 // RefExemplar is an exemplar with the labels, timestamp, value the exemplar was collected/observed with, and a reference to a series.
@@ -253,23 +255,31 @@ func (d *Decoder) Metadata(rec []byte, metadata []RefMetadata) ([]RefMetadata, e
 		// We're currently aware of two more metadata fields other than TYPE; that is UNIT and HELP.
 		// We can skip the rest of the fields (if we encounter any), but we must decode them anyway
 		// so we can correctly align with the start with the next metadata record.
-		var unit, help string
+		var unit, help, fieldValueStr string
+		var ct, fieldValueInt int64
 		for i := 0; i < numFields; i++ {
 			fieldName := dec.UvarintStr()
-			fieldValue := dec.UvarintStr()
 			switch fieldName {
 			case unitMetaName:
-				unit = fieldValue
+				fieldValueStr = dec.UvarintStr()
+				unit = fieldValueStr
 			case helpMetaName:
-				help = fieldValue
+				fieldValueStr = dec.UvarintStr()
+				help = fieldValueStr
+			case createdTimestampName:
+				fieldValueInt = dec.Varint64()
+				ct = fieldValueInt
+			default:
+				_ = dec.UvarintStr() // To be skipped
 			}
 		}
 
 		metadata = append(metadata, RefMetadata{
-			Ref:  chunks.HeadSeriesRef(ref),
-			Type: typ,
-			Unit: unit,
-			Help: help,
+			Ref:              chunks.HeadSeriesRef(ref),
+			Type:             typ,
+			Unit:             unit,
+			Help:             help,
+			CreatedTimestamp: ct,
 		})
 	}
 	if dec.Err() != nil {
@@ -615,11 +625,13 @@ func (e *Encoder) Metadata(metadata []RefMetadata, b []byte) []byte {
 
 		buf.PutByte(m.Type)
 
-		buf.PutUvarint(2) // num_fields: We currently have two more metadata fields, UNIT and HELP.
+		buf.PutUvarint(3) // num_fields: We currently have three more metadata fields, UNIT, HELP, and CREATED_TIMESTAMP.
 		buf.PutUvarintStr(unitMetaName)
 		buf.PutUvarintStr(m.Unit)
 		buf.PutUvarintStr(helpMetaName)
 		buf.PutUvarintStr(m.Help)
+		buf.PutUvarintStr(createdTimestampName)
+		buf.PutVarint64(m.CreatedTimestamp)
 	}
 
 	return buf.Get()

tsdb/record/record_test.go

@@ -49,22 +49,25 @@ func TestRecord_EncodeDecode(t *testing.T) {
 
 	metadata := []RefMetadata{
 		{
-			Ref:  100,
-			Type: uint8(Counter),
-			Unit: "",
-			Help: "some magic counter",
+			Ref:              100,
+			Type:             uint8(Counter),
+			Unit:             "",
+			Help:             "some magic counter",
+			CreatedTimestamp: 1234,
 		},
 		{
-			Ref:  1,
-			Type: uint8(Counter),
-			Unit: "seconds",
-			Help: "CPU time counter",
+			Ref:              1,
+			Type:             uint8(Counter),
+			Unit:             "seconds",
+			Help:             "CPU time counter",
+			CreatedTimestamp: 1000,
 		},
 		{
-			Ref:  147741,
-			Type: uint8(Gauge),
-			Unit: "percentage",
-			Help: "current memory usage",
+			Ref:              147741,
+			Type:             uint8(Gauge),
+			Unit:             "percentage",
+			Help:             "current memory usage",
+			CreatedTimestamp: 1020,
 		},
 	}
 	decMetadata, err := dec.Metadata(enc.Metadata(metadata, nil), nil)
@@ -329,21 +332,25 @@ func TestRecord_MetadataDecodeUnknownExtraFields(t *testing.T) {
 	// Write first metadata entry, all known fields.
 	enc.PutUvarint64(101)
 	enc.PutByte(byte(Counter))
-	enc.PutUvarint(2)
+	enc.PutUvarint(3)
 	enc.PutUvarintStr(unitMetaName)
 	enc.PutUvarintStr("")
 	enc.PutUvarintStr(helpMetaName)
 	enc.PutUvarintStr("some magic counter")
+	enc.PutUvarintStr(createdTimestampName)
+	enc.PutVarint64(1234)
 
 	// Write second metadata entry, known fields + unknown fields.
 	enc.PutUvarint64(99)
 	enc.PutByte(byte(Counter))
-	enc.PutUvarint(3)
+	enc.PutUvarint(4)
 	// Known fields.
 	enc.PutUvarintStr(unitMetaName)
 	enc.PutUvarintStr("seconds")
 	enc.PutUvarintStr(helpMetaName)
 	enc.PutUvarintStr("CPU time counter")
+	enc.PutUvarintStr(createdTimestampName)
+	enc.PutVarint64(1000)
 	// Unknown fields.
 	enc.PutUvarintStr("an extra field name to be skipped")
 	enc.PutUvarintStr("with its value")
@@ -351,7 +358,7 @@ func TestRecord_MetadataDecodeUnknownExtraFields(t *testing.T) {
 	// Write third metadata entry, with unknown fields and different order.
 	enc.PutUvarint64(47250)
 	enc.PutByte(byte(Gauge))
-	enc.PutUvarint(4)
+	enc.PutUvarint(5)
 	enc.PutUvarintStr("extra name one")
 	enc.PutUvarintStr("extra value one")
 	enc.PutUvarintStr(helpMetaName)
@@ -360,6 +367,8 @@ func TestRecord_MetadataDecodeUnknownExtraFields(t *testing.T) {
 	enc.PutUvarintStr("extra value two")
 	enc.PutUvarintStr(unitMetaName)
 	enc.PutUvarintStr("percentage")
+	enc.PutUvarintStr(createdTimestampName)
+	enc.PutVarint64(1020)
 
 	// Should yield known fields for all entries and skip over unknown fields.
 	expectedMetadata := []RefMetadata{
@@ -368,16 +377,19 @@ func TestRecord_MetadataDecodeUnknownExtraFields(t *testing.T) {
 			Type: uint8(Counter),
 			Unit: "",
 			Help: "some magic counter",
+			CreatedTimestamp: 1234,
 		}, {
 			Ref:  99,
 			Type: uint8(Counter),
 			Unit: "seconds",
 			Help: "CPU time counter",
+			CreatedTimestamp: 1000,
 		}, {
 			Ref:  47250,
 			Type: uint8(Gauge),
 			Unit: "percentage",
 			Help: "current memory usage",
+			CreatedTimestamp: 1020,
 		},
 	}
 

web/api/v1/api.go

@@ -1288,7 +1288,7 @@ func (api *API) metricMetadata(r *http.Request) apiFuncResult {
 		for _, t := range tt {
 			if metric == "" {
 				for _, mm := range t.ListMetadata() {
-					m := metadata.Metadata{Type: mm.Type, Help: mm.Help, Unit: mm.Unit}
+					m := metadata.Metadata{Type: mm.Type, Help: mm.Help, Unit: mm.Unit, CreatedTimestamp: mm.CreatedTimestamp}
 					ms, ok := metrics[mm.Metric]
 
 					if limitPerMetric > 0 && len(ms) >= limitPerMetric {

web/api/v1/api_test.go

@@ -1137,7 +1137,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 	}
 
 	tests := []test{
-		{
+		{ // 0
 			endpoint: api.query,
 			query: url.Values{
 				"query": []string{"2"},
@@ -1151,7 +1151,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 				},
 			},
 		},
-		{
+		{ // 1
 			endpoint: api.query,
 			query: url.Values{
 				"query": []string{"0.333"},
@@ -1165,7 +1165,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 				},
 			},
 		},
-		{
+		{ // 2
 			endpoint: api.query,
 			query: url.Values{
 				"query": []string{"0.333"},
@@ -1179,7 +1179,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 				},
 			},
 		},
-		{
+		{ // 3
 			endpoint: api.query,
 			query: url.Values{
 				"query": []string{"0.333"},
@@ -1192,7 +1192,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 				},
 			},
 		},
-		{
+		{ // 4
 			endpoint: api.queryRange,
 			query: url.Values{
 				"query": []string{"time()"},
@@ -1215,7 +1215,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			},
 		},
 		// Test empty vector result
-		{
+		{ // 5
 			endpoint: api.query,
 			query: url.Values{
 				"query": []string{"bottomk(2, notExists)"},
@@ -1223,7 +1223,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			responseAsJSON: `{"resultType":"vector","result":[]}`,
 		},
 		// Test empty matrix result
-		{
+		{ // 6
 			endpoint: api.queryRange,
 			query: url.Values{
 				"query": []string{"bottomk(2, notExists)"},
@@ -1234,7 +1234,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			responseAsJSON: `{"resultType":"matrix","result":[]}`,
 		},
 		// Missing query params in range queries.
-		{
+		{ // 7
 			endpoint: api.queryRange,
 			query: url.Values{
 				"query": []string{"time()"},
@@ -1243,7 +1243,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			},
 			errType: errorBadData,
 		},
-		{
+		{ // 8
 			endpoint: api.queryRange,
 			query: url.Values{
 				"query": []string{"time()"},
@@ -1252,7 +1252,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			},
 			errType: errorBadData,
 		},
-		{
+		{ // 9
 			endpoint: api.queryRange,
 			query: url.Values{
 				"query": []string{"time()"},
@@ -1262,7 +1262,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			errType: errorBadData,
 		},
 		// Bad query expression.
-		{
+		{ // 10
 			endpoint: api.query,
 			query: url.Values{
 				"query": []string{"invalid][query"},
@@ -1270,7 +1270,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			},
 			errType: errorBadData,
 		},
-		{
+		{ // 11
 			endpoint: api.queryRange,
 			query: url.Values{
 				"query": []string{"invalid][query"},
@@ -1281,7 +1281,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			errType: errorBadData,
 		},
 		// Invalid step.
-		{
+		{ // 12
 			endpoint: api.queryRange,
 			query: url.Values{
 				"query": []string{"time()"},
@@ -1292,7 +1292,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			errType: errorBadData,
 		},
 		// Start after end.
-		{
+		{ // 13
 			endpoint: api.queryRange,
 			query: url.Values{
 				"query": []string{"time()"},
@@ -1303,7 +1303,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			errType: errorBadData,
 		},
 		// Start overflows int64 internally.
-		{
+		{ // 14
 			endpoint: api.queryRange,
 			query: url.Values{
 				"query": []string{"time()"},
@@ -1313,21 +1313,21 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			},
 			errType: errorBadData,
 		},
-		{
+		{ // 15
 			endpoint: api.formatQuery,
 			query: url.Values{
 				"query": []string{"foo+bar"},
 			},
 			response: "foo + bar",
 		},
-		{
+		{ // 16
 			endpoint: api.formatQuery,
 			query: url.Values{
 				"query": []string{"invalid_expression/"},
 			},
 			errType: errorBadData,
 		},
-		{
+		{ // 17
 			endpoint: api.series,
 			query: url.Values{
 				"match[]": []string{`test_metric2`},
@@ -1336,14 +1336,14 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 				labels.FromStrings("__name__", "test_metric2", "foo", "boo"),
 			},
 		},
-		{
+		{ // 18
 			endpoint: api.series,
 			query: url.Values{
 				"match[]": []string{`{foo=""}`},
 			},
 			errType: errorBadData,
 		},
-		{
+		{ // 19
 			endpoint: api.series,
 			query: url.Values{
 				"match[]": []string{`test_metric1{foo=~".+o"}`},
@@ -1352,7 +1352,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 				labels.FromStrings("__name__", "test_metric1", "foo", "boo"),
 			},
 		},
-		{
+		{ // 20
 			endpoint: api.series,
 			query: url.Values{
 				"match[]": []string{`test_metric1{foo=~".+o$"}`, `test_metric1{foo=~".+o"}`},
@@ -1362,7 +1362,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			},
 		},
 		// Try to overlap the selected series set as much as possible to test the result de-duplication works well.
-		{
+		{ // 21
 			endpoint: api.series,
 			query: url.Values{
 				"match[]": []string{`test_metric4{foo=~".+o$"}`, `test_metric4{dup=~"^1"}`},
@@ -1373,7 +1373,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 				labels.FromStrings("__name__", "test_metric4", "foo", "boo"),
 			},
 		},
-		{
+		{ // 22
 			endpoint: api.series,
 			query: url.Values{
 				"match[]": []string{`test_metric1{foo=~".+o"}`, `none`},
@@ -1383,7 +1383,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			},
 		},
 		// Start and end before series starts.
-		{
+		{ // 23
 			endpoint: api.series,
 			query: url.Values{
 				"match[]": []string{`test_metric2`},
@@ -1393,7 +1393,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			response: []labels.Labels{},
 		},
 		// Start and end after series ends.
-		{
+		{ // 24
 			endpoint: api.series,
 			query: url.Values{
 				"match[]": []string{`test_metric2`},
@@ -1403,7 +1403,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			response: []labels.Labels{},
 		},
 		// Start before series starts, end after series ends.
-		{
+		{ // 25
 			endpoint: api.series,
 			query: url.Values{
 				"match[]": []string{`test_metric2`},
@@ -1415,7 +1415,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			},
 		},
 		// Start and end within series.
-		{
+		{ // 26
 			endpoint: api.series,
 			query: url.Values{
 				"match[]": []string{`test_metric2`},
@@ -1427,7 +1427,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			},
 		},
 		// Start within series, end after.
-		{
+		{ // 27
 			endpoint: api.series,
 			query: url.Values{
 				"match[]": []string{`test_metric2`},
@@ -1439,7 +1439,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			},
 		},
 		// Start before series, end within series.
-		{
+		{ // 28
 			endpoint: api.series,
 			query: url.Values{
 				"match[]": []string{`test_metric2`},
@@ -1451,7 +1451,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			},
 		},
 		// Series request with limit.
-		{
+		{ // 29
 			endpoint: api.series,
 			query: url.Values{
 				"match[]": []string{"test_metric1"},
@@ -1460,7 +1460,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			responseLen:   1, // API does not specify which particular value will come back.
 			warningsCount: 1,
 		},
-		{
+		{ // 30
 			endpoint: api.series,
 			query: url.Values{
 				"match[]": []string{"test_metric1"},
@@ -1469,7 +1469,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			responseLen:   2, // API does not specify which particular value will come back.
 			warningsCount: 0, // No warnings if limit isn't exceeded.
 		},
-		{
+		{ // 31
 			endpoint: api.series,
 			query: url.Values{
 				"match[]": []string{"test_metric1"},
@@ -1479,15 +1479,15 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			warningsCount: 0, // No warnings if limit isn't exceeded.
 		},
 		// Missing match[] query params in series requests.
-		{
+		{ // 32
 			endpoint: api.series,
 			errType:  errorBadData,
 		},
-		{
+		{ // 33
 			endpoint: api.dropSeries,
 			errType:  errorInternal,
 		},
-		{
+		{ // 34
 			endpoint: api.targets,
 			response: &TargetDiscovery{
 				ActiveTargets: []*Target{
@@ -1533,7 +1533,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 				DroppedTargetCounts: map[string]int{"blackbox": 1},
 			},
 		},
-		{
+		{ // 35
 			endpoint: api.targets,
 			query: url.Values{
 				"state": []string{"any"},
@@ -1582,7 +1582,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 				DroppedTargetCounts: map[string]int{"blackbox": 1},
 			},
 		},
-		{
+		{ // 36
 			endpoint: api.targets,
 			query: url.Values{
 				"state": []string{"active"},
@@ -1619,7 +1619,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 				DroppedTargets: []*DroppedTarget{},
 			},
 		},
-		{
+		{ // 37
 			endpoint: api.targets,
 			query: url.Values{
 				"state": []string{"Dropped"},
@@ -1642,7 +1642,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			},
 		},
 		// With a matching metric.
-		{
+		{ // 38
 			endpoint: api.targetMetadata,
 			query: url.Values{
 				"metric": []string{"go_threads"},
@@ -1672,7 +1672,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			},
 		},
 		// With a matching target.
-		{
+		{ // 39
 			endpoint: api.targetMetadata,
 			query: url.Values{
 				"match_target": []string{"{job=\"blackbox\"}"},
@@ -1703,7 +1703,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			},
 		},
 		// Without a target or metric.
-		{
+		{ // 40
 			endpoint: api.targetMetadata,
 			metadata: []targetMetadata{
 				{
@@ -1757,14 +1757,14 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			},
 		},
 		// Without a matching metric.
-		{
+		{ // 41
 			endpoint: api.targetMetadata,
 			query: url.Values{
 				"match_target": []string{"{job=\"non-existentblackbox\"}"},
 			},
 			response: []metricMetadata{},
 		},
-		{
+		{ // 42
 			endpoint: api.alertmanagers,
 			response: &AlertmanagerDiscovery{
 				ActiveAlertmanagers: []*AlertmanagerTarget{
@@ -1780,7 +1780,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			},
 		},
 		// With metadata available.
-		{
+		{ // 43
 			endpoint: api.metricMetadata,
 			metadata: []targetMetadata{
 				{
@@ -1797,20 +1797,21 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 							Type:   model.MetricTypeGauge,
 							Help:   "Information about the Go environment.",
 							Unit:   "",
+							CreatedTimestamp: 1000,
 						},
 					},
 				},
 			},
 			response: map[string][]metadata.Metadata{
 				"prometheus_engine_query_duration_seconds": {{Type: model.MetricTypeSummary, Help: "Query timings", Unit: ""}},
-				"go_info": {{Type: model.MetricTypeGauge, Help: "Information about the Go environment.", Unit: ""}},
+				"go_info": {{Type: model.MetricTypeGauge, Help: "Information about the Go environment.", Unit: "", CreatedTimestamp: 1000}},
 			},
 			responseAsJSON: `{"prometheus_engine_query_duration_seconds":[{"type":"summary","unit":"",
-"help":"Query timings"}], "go_info":[{"type":"gauge","unit":"",
-"help":"Information about the Go environment."}]}`,
+"help":"Query timings", "created_timestamp": 0}], "go_info":[{"type":"gauge","unit":"",
+"help":"Information about the Go environment.", "created_timestamp": 1000}]}`,
 		},
 		// With duplicate metadata for a metric that comes from different targets.
-		{
+		{ // 44
 			endpoint: api.metricMetadata,
 			metadata: []targetMetadata{
 				{
@@ -1840,10 +1841,10 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 				"go_threads": {{Type: model.MetricTypeGauge, Help: "Number of OS threads created"}},
 			},
 			responseAsJSON: `{"go_threads": [{"type":"gauge","unit":"",
-"help":"Number of OS threads created"}]}`,
+"help":"Number of OS threads created", "created_timestamp": 0}]}`,
 		},
 		// With non-duplicate metadata for the same metric from different targets.
-		{
+		{ // 45
 			endpoint: api.metricMetadata,
 			metadata: []targetMetadata{
 				{
@@ -1876,8 +1877,8 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 				},
 			},
 			responseAsJSON: `{"go_threads": [{"type":"gauge","unit":"",
-"help":"Number of OS threads created"},{"type":"gauge","unit":"",
-"help":"Number of OS threads that were created."}]}`,
+"help":"Number of OS threads created", "created_timestamp": 0},{"type":"gauge","unit":"",
+"help":"Number of OS threads that were created.", "created_timestamp": 0}]}`,
 			sorter: func(m interface{}) {
 				v := m.(map[string][]metadata.Metadata)["go_threads"]
 
@@ -1887,7 +1888,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			},
 		},
 		// With a limit for the number of metrics returned.
-		{
+		{ // 46
 			endpoint: api.metricMetadata,
 			query: url.Values{
 				"limit": []string{"2"},
@@ -1925,7 +1926,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			responseLen: 2,
 		},
 		// With a limit for the number of metadata per metric.
-		{
+		{ // 47
 			endpoint: api.metricMetadata,
 			query:    url.Values{"limit_per_metric": []string{"1"}},
 			metadata: []targetMetadata{
@@ -1961,10 +1962,10 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 					{Type: model.MetricTypeSummary, Help: "A summary of the GC invocation durations."},
 				},
 			},
-			responseAsJSON: `{"go_gc_duration_seconds":[{"help":"A summary of the GC invocation durations.","type":"summary","unit":""}],"go_threads": [{"type":"gauge","unit":"","help":"Number of OS threads created"}]}`,
+			responseAsJSON: `{"go_gc_duration_seconds":[{"help":"A summary of the GC invocation durations.","type":"summary","unit":"", "created_timestamp": 0}],"go_threads": [{"type":"gauge","unit":"","help":"Number of OS threads created", "created_timestamp": 0}]}`,
 		},
 		// With a limit for the number of metadata per metric and per metric.
-		{
+		{ // 48
 			endpoint: api.metricMetadata,
 			query:    url.Values{"limit_per_metric": []string{"1"}, "limit": []string{"1"}},
 			metadata: []targetMetadata{
@@ -1997,7 +1998,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 		},
 
 		// With a limit for the number of metadata per metric and per metric, while having multiple targets.
-		{
+		{ // 49
 			endpoint: api.metricMetadata,
 			query:    url.Values{"limit_per_metric": []string{"1"}, "limit": []string{"1"}},
 			metadata: []targetMetadata{
@@ -2046,7 +2047,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			responseMetadataTotal: 1,
 		},
 		// When requesting a specific metric that is present.
-		{
+		{ // 50
 			endpoint: api.metricMetadata,
 			query:    url.Values{"metric": []string{"go_threads"}},
 			metadata: []targetMetadata{
@@ -2085,7 +2086,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 					{Type: model.MetricTypeGauge, Help: "Number of OS threads that were created."},
 				},
 			},
-			responseAsJSON: `{"go_threads": [{"type":"gauge","unit":"","help":"Number of OS threads created"},{"type":"gauge","unit":"","help":"Number of OS threads that were created."}]}`,
+			responseAsJSON: `{"go_threads": [{"type":"gauge","unit":"","help":"Number of OS threads created", "created_timestamp": 0},{"type":"gauge","unit":"","help":"Number of OS threads that were created.", "created_timestamp": 0}]}`,
 			sorter: func(m interface{}) {
 				v := m.(map[string][]metadata.Metadata)["go_threads"]
 
@@ -2095,7 +2096,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			},
 		},
 		// With a specific metric that is not present.
-		{
+		{ // 51
 			endpoint: api.metricMetadata,
 			query:    url.Values{"metric": []string{"go_gc_duration_seconds"}},
 			metadata: []targetMetadata{
@@ -2114,21 +2115,21 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			response: map[string][]metadata.Metadata{},
 		},
 		// With no available metadata.
-		{
+		{ // 52
 			endpoint: api.metricMetadata,
 			response: map[string][]metadata.Metadata{},
 		},
-		{
+		{ // 53
 			endpoint: api.serveConfig,
 			response: &prometheusConfig{
 				YAML: samplePrometheusCfg.String(),
 			},
 		},
-		{
+		{ // 54
 			endpoint: api.serveFlags,
 			response: sampleFlagMap,
 		},
-		{
+		{ // 55
 			endpoint: api.alerts,
 			response: &AlertDiscovery{
 				Alerts: []*Alert{
@@ -2149,7 +2150,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 				}
 			},
 		},
-		{
+		{ // 56
 			endpoint: api.rules,
 			response: &RuleDiscovery{
 				RuleGroups: []*RuleGroup{
@@ -2241,7 +2242,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			},
 			zeroFunc: rulesZeroFunc,
 		},
-		{
+		{ // 57
 			endpoint: api.rules,
 			query: url.Values{
 				"exclude_alerts": []string{"true"},
@@ -2329,7 +2330,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			},
 			zeroFunc: rulesZeroFunc,
 		},
-		{
+		{ // 58
 			endpoint: api.rules,
 			query: url.Values{
 				"type": []string{"alert"},
@@ -2410,7 +2411,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			},
 			zeroFunc: rulesZeroFunc,
 		},
-		{
+		{ // 59
 			endpoint: api.rules,
 			query: url.Values{
 				"type": []string{"record"},
@@ -2443,7 +2444,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			},
 			zeroFunc: rulesZeroFunc,
 		},
-		{
+		{ // 60
 			endpoint: api.rules,
 			query:    url.Values{"rule_name[]": []string{"test_metric4"}},
 			response: &RuleDiscovery{
@@ -2471,12 +2472,12 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			},
 			zeroFunc: rulesZeroFunc,
 		},
-		{
+		{ // 61
 			endpoint: api.rules,
 			query:    url.Values{"rule_group[]": []string{"respond-with-nothing"}},
 			response: &RuleDiscovery{RuleGroups: []*RuleGroup{}},
 		},
-		{
+		{ // 62
 			endpoint: api.rules,
 			query:    url.Values{"file[]": []string{"/path/to/file"}, "rule_name[]": []string{"test_metric4"}},
 			response: &RuleDiscovery{
@@ -2504,7 +2505,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			},
 			zeroFunc: rulesZeroFunc,
 		},
-		{
+		{ // 63
 			endpoint: api.rules,
 			query: url.Values{
 				"match[]": []string{`{testlabel="rule"}`},
@@ -2541,7 +2542,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			},
 			zeroFunc: rulesZeroFunc,
 		},
-		{
+		{ // 64
 			endpoint: api.rules,
 			query: url.Values{
 				"type":    []string{"alert"},
@@ -2572,7 +2573,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			},
 			zeroFunc: rulesZeroFunc,
 		},
-		{
+		{ // 65
 			endpoint: api.rules,
 			query: url.Values{
 				"match[]": []string{`{testlabel="abc"}`},
@@ -2582,7 +2583,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			},
 		},
 		// This is testing OR condition, the api response should return rule if it matches one of the label selector
-		{
+		{ // 66
 			endpoint: api.rules,
 			query: url.Values{
 				"match[]": []string{`{testlabel="abc"}`, `{testlabel="rule"}`},
@@ -2619,7 +2620,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			},
 			zeroFunc: rulesZeroFunc,
 		},
-		{
+		{ // 67
 			endpoint: api.rules,
 			query: url.Values{
 				"type":    []string{"record"},
@@ -2646,7 +2647,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			},
 			zeroFunc: rulesZeroFunc,
 		},
-		{
+		{ // 68
 			endpoint: api.rules,
 			query: url.Values{
 				"type":    []string{"alert"},
@@ -2677,7 +2678,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 			},
 			zeroFunc: rulesZeroFunc,
 		},
-		{
+		{ // 69
 			endpoint: api.queryExemplars,
 			query: url.Values{
 				"query": []string{`test_metric3{foo="boo"} - test_metric4{foo="bar"}`},
@@ -2710,7 +2711,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 				},
 			},
 		},
-		{
+		{ // 70
 			endpoint: api.queryExemplars,
 			query: url.Values{
 				"query": []string{`{foo="boo"}`},
@@ -2730,7 +2731,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 				},
 			},
 		},
-		{
+		{ // 71
 			endpoint: api.queryExemplars,
 			query: url.Values{
 				"query": []string{`{foo="boo"}`},
@@ -2753,7 +2754,7 @@ func testEndpoints(t *testing.T, api *API, tr *testTargetRetriever, es storage.E
 				},
 			},
 		},
-		{
+		{ // 72
 			endpoint: api.queryExemplars,
 			query: url.Values{
 				"query": []string{`{__name__="test_metric5"}`},