Phase out native histogram feature flag

The detailed plan for this is laid out in
https://github.com/prometheus/prometheus/issues/16572 .

This commit adds a global and local scrape config option
`scrape_native_histograms`, which has to be set to true to ingest
native histograms.

To ease the transition, the feature flag is changed to simply set the
default of `scrape_native_histograms` to true.

Further implications:

- The default scrape protocols now depend on the
  `scrape_native_histograms` setting.
- Everywhere else, histograms are now "on by default".

Documentation beyond the one for the feature flag and the scrape
config are deliberately left out. See
https://github.com/prometheus/prometheus/pull/17232 for that.

Signed-off-by: beorn7 <beorn@grafana.com>

model/textparse/benchmark_test.go

@@ -149,7 +149,7 @@ func benchParse(b *testing.B, data []byte, parser string) {
 		}
 	case "promproto":
 		newParserFn = func(b []byte, st *labels.SymbolTable) Parser {
-			return NewProtobufParser(b, true, false, false, st)
+			return NewProtobufParser(b, false, true, false, false, st)
 		}
 	case "omtext":
 		newParserFn = func(b []byte, st *labels.SymbolTable) Parser {
@@ -276,7 +276,7 @@ func BenchmarkCreatedTimestampPromProto(b *testing.B) {
 	data := createTestProtoBuf(b).Bytes()
 
 	st := labels.NewSymbolTable()
-	p := NewProtobufParser(data, true, false, false, st)
+	p := NewProtobufParser(data, false, true, false, false, st)
 
 	found := false
 Inner:

model/textparse/interface.go

@@ -127,6 +127,17 @@ type ParserOptions struct {
 	// in the parsed metrics.
 	EnableTypeAndUnitLabels bool
 
+	// IgnoreNativeHistograms causes the parser to completely ignore all
+	// parts of native histograms, but to keep the ability to convert
+	// classic histograms to NHCB. This has the implication that even a
+	// histogram that has some native parts but not a single classic bucket
+	// will be parsed as a classic histogram (with only the +Inf bucket and
+	// count and sum). Setting this also allows converting a classic
+	// histogram that already has a native representation to an NHCB. This
+	// option has no effect on parsers for formats that do not support
+	// native histograms.
+	IgnoreNativeHistograms bool
+
 	// ConvertClassicHistogramsToNHCB enables conversion of classic histograms
 	// to native histogram custom buckets (NHCB) format.
 	ConvertClassicHistogramsToNHCB bool
@@ -168,7 +179,14 @@ func New(b []byte, contentType string, st *labels.SymbolTable, opts ParserOption
 			o.enableTypeAndUnitLabels = opts.EnableTypeAndUnitLabels
 		})
 	case "application/vnd.google.protobuf":
-		return NewProtobufParser(b, opts.KeepClassicOnClassicAndNativeHistograms, opts.ConvertClassicHistogramsToNHCB, opts.EnableTypeAndUnitLabels, st), err
+		return NewProtobufParser(
+			b,
+			opts.IgnoreNativeHistograms,
+			opts.KeepClassicOnClassicAndNativeHistograms,
+			opts.ConvertClassicHistogramsToNHCB,
+			opts.EnableTypeAndUnitLabels,
+			st,
+		), err
 	case "text/plain":
 		baseParser = NewPromParser(b, st, opts.EnableTypeAndUnitLabels)
 	default:

model/textparse/protobufparse.go

@@ -77,6 +77,8 @@ type ProtobufParser struct {
 	// that we have to decode the next MetricDescriptor.
 	state Entry
 
+	// Whether to completely ignore any native parts of histograms.
+	ignoreNativeHistograms bool
 	// Whether to also parse a classic histogram that is also present as a
 	// native histogram.
 	parseClassicHistograms bool
@@ -93,7 +95,11 @@ type ProtobufParser struct {
 }
 
 // NewProtobufParser returns a parser for the payload in the byte slice.
-func NewProtobufParser(b []byte, parseClassicHistograms, convertClassicHistogramsToNHCB, enableTypeAndUnitLabels bool, st *labels.SymbolTable) Parser {
+func NewProtobufParser(
+	b []byte,
+	ignoreNativeHistograms, parseClassicHistograms, convertClassicHistogramsToNHCB, enableTypeAndUnitLabels bool,
+	st *labels.SymbolTable,
+) Parser {
 	builder := labels.NewScratchBuilderWithSymbolTable(st, 16)
 	builder.SetUnsafeAdd(true)
 	return &ProtobufParser{
@@ -102,6 +108,7 @@ func NewProtobufParser(b []byte, parseClassicHistograms, convertClassicHistogram
 		builder:    builder,
 
 		state:                          EntryInvalid,
+		ignoreNativeHistograms:         ignoreNativeHistograms,
 		parseClassicHistograms:         parseClassicHistograms,
 		enableTypeAndUnitLabels:        enableTypeAndUnitLabels,
 		convertClassicHistogramsToNHCB: convertClassicHistogramsToNHCB,
@@ -196,7 +203,7 @@ func (p *ProtobufParser) Histogram() ([]byte, *int64, *histogram.Histogram, *his
 		h  = p.dec.GetHistogram()
 	)
 
-	if !isNativeHistogram(h) {
+	if p.ignoreNativeHistograms || !isNativeHistogram(h) {
 		// This only happens if we have a classic histogram and
 		// we converted it to NHCB already in Next.
 		if *ts != 0 {
@@ -494,7 +501,7 @@ func (p *ProtobufParser) Next() (Entry, error) {
 	case EntryType:
 		t := p.dec.GetType()
 		if t == dto.MetricType_HISTOGRAM || t == dto.MetricType_GAUGE_HISTOGRAM {
-			if !isNativeHistogram(p.dec.GetHistogram()) {
+			if p.ignoreNativeHistograms || !isNativeHistogram(p.dec.GetHistogram()) {
 				p.state = EntrySeries
 				p.fieldPos = -3 // We have not returned anything, let p.Next() increment it to -2.
 				return p.Next()
@@ -515,7 +522,8 @@ func (p *ProtobufParser) Next() (Entry, error) {
 			t == dto.MetricType_GAUGE_HISTOGRAM {
 			// Non-trivial series (complex metrics, with magic suffixes).
 
-			isClassicHistogram := (t == dto.MetricType_HISTOGRAM || t == dto.MetricType_GAUGE_HISTOGRAM) && !isNativeHistogram(p.dec.GetHistogram())
+			isClassicHistogram := (t == dto.MetricType_HISTOGRAM || t == dto.MetricType_GAUGE_HISTOGRAM) &&
+				(p.ignoreNativeHistograms || !isNativeHistogram(p.dec.GetHistogram()))
 			skipSeries := p.convertClassicHistogramsToNHCB && isClassicHistogram && !p.parseClassicHistograms
 
 			// Did we iterate over all the classic representations fields?
@@ -591,10 +599,11 @@ func (p *ProtobufParser) Next() (Entry, error) {
 			return EntryInvalid, err
 		}
 
-		// If this is a metric family does not contain native
-		// histograms, it means we are here thanks to NHCB conversion.
-		// Return to classic histograms for the consistent flow.
-		if !isNativeHistogram(p.dec.GetHistogram()) {
+		// If this metric is not a native histograms or we are ignoring
+		// native histograms, it means we are here thanks to NHCB
+		// conversion. Return to classic histograms for the consistent
+		// flow.
+		if p.ignoreNativeHistograms || !isNativeHistogram(p.dec.GetHistogram()) {
 			return switchToClassic()
 		}