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[EXPORTER] Prometheus exporter: merge metric families across scopes and drop conflicting metric types #4736

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[EXPORTER] Prometheus exporter: merge metric families across scopes and drop conflicting metric types #4736

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[EXPORTER] Prometheus exporter: merge metric families across scopes a…
dashpole Oct 25, 2026
7340a3e
Address review comment: index target MetricFamily in family_index_by_…
dashpole Oct 28, 2026
9566287
Address review comment: skip unsupported aggregations before register…
dashpole Oct 28, 2026
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4 changes: 4 additions & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,10 @@ Increment the:
and empty point guards
[#4738](https://github.com/open-telemetry/opentelemetry-cpp/pull/4738)

* [EXPORTER] Prometheus exporter: merge metric families across scopes and drop
conflicting metric types
[#4736](https://github.com/open-telemetry/opentelemetry-cpp/pull/4736)

## [1.30.0] 2026-10-22

This release contains:
Expand Down
70 changes: 56 additions & 14 deletions exporters/prometheus/src/exporter_utils.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -226,6 +226,12 @@ std::vector<prometheus_client::MetricFamily> PrometheusExporterUtils::TranslateT
&output);
}

std::unordered_map<std::string, std::size_t> family_index_by_name;
for (std::size_t i = 0; i < output.size(); ++i)
{
family_index_by_name.emplace(output[i].name, i);
}

for (const auto &instrumentation_info : data.scope_metric_data_)
{
for (const auto &metric_data : instrumentation_info.metric_data_)
Expand All @@ -234,20 +240,57 @@ std::vector<prometheus_client::MetricFamily> PrometheusExporterUtils::TranslateT
{
continue;
}
prometheus_client::MetricFamily metric_family;
metric_family.help = metric_data.instrument_descriptor.description_;
auto front = metric_data.point_data_attr_.front();
auto kind = getAggregationType(front.point_data);
bool is_monotonic = true;
auto front = metric_data.point_data_attr_.front();
auto kind = getAggregationType(front.point_data);
bool is_monotonic = true;
if (kind == sdk::metrics::AggregationType::kSum)
{
is_monotonic = nostd::get<sdk::metrics::SumPointData>(front.point_data).is_monotonic_;
}
const prometheus_client::MetricType type = TranslateType(kind, is_monotonic);
metric_family.name = MapToPrometheusName(metric_data.instrument_descriptor.name_,
metric_data.instrument_descriptor.unit_, type,
without_units, without_type_suffix);
metric_family.type = type;
if (type == prometheus_client::MetricType::Untyped)
{
OTEL_INTERNAL_LOG_WARN(
"[Prometheus Exporter] TranslateToPrometheus - "
"Unsupported aggregation type for metric '"
<< metric_data.instrument_descriptor.name_ << "'. Dropping metric.");
continue;
}
const std::string name = MapToPrometheusName(metric_data.instrument_descriptor.name_,
metric_data.instrument_descriptor.unit_, type,
without_units, without_type_suffix);
prometheus_client::MetricFamily *metric_family_ptr = nullptr;
auto existing_it = family_index_by_name.find(name);
if (existing_it != family_index_by_name.end())
{
auto &existing_family = output[existing_it->second];
if (existing_family.type != type)
{
OTEL_INTERNAL_LOG_WARN(
"[Prometheus Exporter] TranslateToPrometheus - "
"Instrument type conflict for metric '"
<< name << "'. Dropping conflicting metric.");
continue;
}
if (existing_family.help != metric_data.instrument_descriptor.description_)
{
OTEL_INTERNAL_LOG_WARN(
"[Prometheus Exporter] TranslateToPrometheus - "
"Instrument description conflict for metric '"
<< name << "': '" << metric_data.instrument_descriptor.description_
<< "', using existing description: '" << existing_family.help << "'.");
}
metric_family_ptr = &existing_family;
}
else
{
family_index_by_name.emplace(name, output.size());

@lalitb lalitb Oct 27, 2026

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Can we skip unsupported aggregations before registering the name? A View-configured exponential histogram reserves it as Untyped but emits no points, causing a later supported histogram with the same name to be dropped. Please add a regression test for this case.

@dashpole dashpole Oct 28, 2026

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addressed in 9566287

output.emplace_back();
metric_family_ptr = &output.back();
metric_family_ptr->name = name;
metric_family_ptr->help = metric_data.instrument_descriptor.description_;
metric_family_ptr->type = type;
}
const opentelemetry::sdk::instrumentationscope::InstrumentationScope *scope =
without_otel_scope ? nullptr : instrumentation_info.scope_;

Expand All @@ -269,7 +312,7 @@ std::vector<prometheus_client::MetricFamily> PrometheusExporterUtils::TranslateT
sum = static_cast<double>(nostd::get<int64_t>(histogram_point_data.sum_));
}
SetData(std::vector<double>{sum, static_cast<double>(histogram_point_data.count_)},
boundaries, counts, point_data_attr.attributes, scope, &metric_family,
boundaries, counts, point_data_attr.attributes, scope, metric_family_ptr,
data.resource_);
}
else if (type == prometheus_client::MetricType::Gauge)
Expand All @@ -280,15 +323,15 @@ std::vector<prometheus_client::MetricFamily> PrometheusExporterUtils::TranslateT
auto last_value_point_data =
nostd::get<sdk::metrics::LastValuePointData>(point_data_attr.point_data);
std::vector<metric_sdk::ValueType> values{last_value_point_data.value_};
SetData(values, point_data_attr.attributes, scope, type, &metric_family,
SetData(values, point_data_attr.attributes, scope, type, metric_family_ptr,
data.resource_);
}
else if (nostd::holds_alternative<sdk::metrics::SumPointData>(point_data_attr.point_data))
{
auto sum_point_data =
nostd::get<sdk::metrics::SumPointData>(point_data_attr.point_data);
std::vector<metric_sdk::ValueType> values{sum_point_data.value_};
SetData(values, point_data_attr.attributes, scope, type, &metric_family,
SetData(values, point_data_attr.attributes, scope, type, metric_family_ptr,
data.resource_);
}
else
Expand All @@ -305,7 +348,7 @@ std::vector<prometheus_client::MetricFamily> PrometheusExporterUtils::TranslateT
auto sum_point_data =
nostd::get<sdk::metrics::SumPointData>(point_data_attr.point_data);
std::vector<metric_sdk::ValueType> values{sum_point_data.value_};
SetData(values, point_data_attr.attributes, scope, type, &metric_family,
SetData(values, point_data_attr.attributes, scope, type, metric_family_ptr,
data.resource_);
}
else
Expand All @@ -316,7 +359,6 @@ std::vector<prometheus_client::MetricFamily> PrometheusExporterUtils::TranslateT
}
}
}
output.emplace_back(metric_family);
}
}
return output;
Expand Down
174 changes: 174 additions & 0 deletions exporters/prometheus/test/exporter_utils_test.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -638,4 +638,178 @@ TEST(PrometheusExporterUtils, CrossSourceScopeCollisionsAndArrayAttributes)
}
}

TEST(PrometheusExporterUtils, MultipleScopesMetricFamilyCollisions)
{
Resource resource = Resource::Create(ResourceAttributes{});
auto scope1 = InstrumentationScope::Create("scope_1", "1.0.0");
auto scope2 = InstrumentationScope::Create("scope_2", "2.0.0");
auto scope3 = InstrumentationScope::Create("scope_3", "3.0.0");

metric_sdk::SumPointData counter_point_1{};
counter_point_1.value_ = 10.0;
counter_point_1.is_monotonic_ = true;

metric_sdk::SumPointData counter_point_2{};
counter_point_2.value_ = 20.0;
counter_point_2.is_monotonic_ = true;

metric_sdk::LastValuePointData gauge_point_3{};
gauge_point_3.value_ = 30.0;
gauge_point_3.is_lastvalue_valid_ = true;

// Scope 1 & Scope 2 emit the same metric name & type, but different descriptions.
metric_sdk::MetricData metric_scope_1{
metric_sdk::InstrumentDescriptor{"http.requests", "first description", "s",
metric_sdk::InstrumentType::kCounter,
metric_sdk::InstrumentValueType::kDouble},
metric_sdk::AggregationTemporality::kCumulative, opentelemetry::common::SystemTimestamp{},
opentelemetry::common::SystemTimestamp{},
std::vector<metric_sdk::PointDataAttributes>{{{{"env", "prod"}}, counter_point_1}}};

metric_sdk::MetricData metric_scope_2{
metric_sdk::InstrumentDescriptor{"http.requests", "conflicting description", "ms",
metric_sdk::InstrumentType::kCounter,
metric_sdk::InstrumentValueType::kDouble},
metric_sdk::AggregationTemporality::kCumulative, opentelemetry::common::SystemTimestamp{},
opentelemetry::common::SystemTimestamp{},
std::vector<metric_sdk::PointDataAttributes>{{{{"env", "dev"}}, counter_point_2}}};

// Scope 3 emits a conflicting type (Gauge) that maps to the same Prometheus name when
// without_units=true and without_type_suffix=true.
metric_sdk::MetricData metric_scope_3_conflict_type{
metric_sdk::InstrumentDescriptor{"http_requests", "gauge description", "1",
metric_sdk::InstrumentType::kObservableGauge,
metric_sdk::InstrumentValueType::kDouble},
metric_sdk::AggregationTemporality::kCumulative, opentelemetry::common::SystemTimestamp{},
opentelemetry::common::SystemTimestamp{},
std::vector<metric_sdk::PointDataAttributes>{{{{"env", "stage"}}, gauge_point_3}}};

metric_sdk::ResourceMetrics data{
&resource,
std::vector<metric_sdk::ScopeMetrics>{
{scope1.get(), std::vector<metric_sdk::MetricData>{metric_scope_1}},
{scope2.get(), std::vector<metric_sdk::MetricData>{metric_scope_2}},
{scope3.get(), std::vector<metric_sdk::MetricData>{metric_scope_3_conflict_type}}}};

// With without_units=true and without_type_suffix=true, all three map to "http_requests".
// Scope 1 and Scope 2 (both Counter) should be merged into a single MetricFamily keeping
// "first description", while Scope 3 (Gauge) should be dropped due to type conflict.
auto translated = PrometheusExporterUtils::TranslateToPrometheus(
data, /*populate_target_info=*/false, /*without_otel_scope=*/false,
/*without_units=*/true, /*without_type_suffix=*/true);

ASSERT_EQ(translated.size(), 1U);
EXPECT_EQ(translated[0].name, "http_requests");
EXPECT_EQ(translated[0].help, "first description");
EXPECT_EQ(translated[0].type, prometheus_client::MetricType::Counter);
ASSERT_EQ(translated[0].metric.size(), 2U);
EXPECT_DOUBLE_EQ(translated[0].metric[0].counter.value, 10.0);
EXPECT_DOUBLE_EQ(translated[0].metric[1].counter.value, 20.0);
}

TEST(PrometheusExporterUtils, TargetInfoMetricFamilyCollision)
{
Resource resource = Resource::Create(ResourceAttributes{{"service.name", "test_service"}});
auto scope = InstrumentationScope::Create("scope_1", "1.0.0");

metric_sdk::LastValuePointData gauge_point{};
gauge_point.value_ = 42.0;
gauge_point.is_lastvalue_valid_ = true;

metric_sdk::SumPointData counter_point{};
counter_point.value_ = 7.0;
counter_point.is_monotonic_ = true;

// A unitless gauge named "target" maps to family name "target", which collides with the
// MetricFamily{"target", MetricType::Info} emitted by SetTarget when populate_target_info=true.
metric_sdk::MetricData colliding_target_gauge{
metric_sdk::InstrumentDescriptor{"target", "conflicting gauge description", "",
metric_sdk::InstrumentType::kObservableGauge,
metric_sdk::InstrumentValueType::kDouble},
metric_sdk::AggregationTemporality::kCumulative, opentelemetry::common::SystemTimestamp{},
opentelemetry::common::SystemTimestamp{},
std::vector<metric_sdk::PointDataAttributes>{{{{"env", "prod"}}, gauge_point}}};

metric_sdk::MetricData counter_metric{
metric_sdk::InstrumentDescriptor{"http.requests", "requests description", "1",
metric_sdk::InstrumentType::kCounter,
metric_sdk::InstrumentValueType::kDouble},
metric_sdk::AggregationTemporality::kCumulative, opentelemetry::common::SystemTimestamp{},
opentelemetry::common::SystemTimestamp{},
std::vector<metric_sdk::PointDataAttributes>{{{{"env", "prod"}}, counter_point}}};

metric_sdk::ResourceMetrics data{
&resource, std::vector<metric_sdk::ScopeMetrics>{
{scope.get(), std::vector<metric_sdk::MetricData>{colliding_target_gauge,
counter_metric}}}};

auto translated = PrometheusExporterUtils::TranslateToPrometheus(
data, /*populate_target_info=*/true, /*without_otel_scope=*/false,
/*without_units=*/false, /*without_type_suffix=*/false);

ASSERT_EQ(translated.size(), 2U);
EXPECT_EQ(translated[0].name, "target");
EXPECT_EQ(translated[0].help, "Target metadata");
EXPECT_EQ(translated[0].type, prometheus_client::MetricType::Info);
ASSERT_EQ(translated[0].metric.size(), 1U);

EXPECT_EQ(translated[1].name, "http_requests_total");
EXPECT_EQ(translated[1].type, prometheus_client::MetricType::Counter);
ASSERT_EQ(translated[1].metric.size(), 1U);
EXPECT_DOUBLE_EQ(translated[1].metric[0].counter.value, 7.0);
}

TEST(PrometheusExporterUtils, UnsupportedAggregationDoesNotReserveMetricFamilyName)
{
Resource resource = Resource::Create(ResourceAttributes{});
auto scope1 = InstrumentationScope::Create("scope_1", "1.0.0");
auto scope2 = InstrumentationScope::Create("scope_2", "2.0.0");

metric_sdk::Base2ExponentialHistogramPointData exp_histogram_point{};
exp_histogram_point.count_ = 5;
exp_histogram_point.sum_ = 15.0;

metric_sdk::HistogramPointData histogram_point{};
histogram_point.boundaries_ = {10.0, 20.0};
histogram_point.counts_ = {1, 2, 1};
histogram_point.count_ = 4;
histogram_point.sum_ = 45.0;

// An unsupported Base2ExponentialHistogram aggregation should be skipped without reserving
// the metric family name as Untyped, allowing a subsequent supported Histogram with the same
// name to be exported.
metric_sdk::MetricData unsupported_exp_histogram{
metric_sdk::InstrumentDescriptor{"http.server.duration", "exp histogram description", "s",
metric_sdk::InstrumentType::kHistogram,
metric_sdk::InstrumentValueType::kDouble},
metric_sdk::AggregationTemporality::kCumulative, opentelemetry::common::SystemTimestamp{},
opentelemetry::common::SystemTimestamp{},
std::vector<metric_sdk::PointDataAttributes>{{{{"env", "prod"}}, exp_histogram_point}}};

metric_sdk::MetricData supported_histogram{
metric_sdk::InstrumentDescriptor{"http.server.duration", "histogram description", "s",
metric_sdk::InstrumentType::kHistogram,
metric_sdk::InstrumentValueType::kDouble},
metric_sdk::AggregationTemporality::kCumulative, opentelemetry::common::SystemTimestamp{},
opentelemetry::common::SystemTimestamp{},
std::vector<metric_sdk::PointDataAttributes>{{{{"env", "prod"}}, histogram_point}}};

metric_sdk::ResourceMetrics data{
&resource, std::vector<metric_sdk::ScopeMetrics>{
{scope1.get(), std::vector<metric_sdk::MetricData>{unsupported_exp_histogram}},
{scope2.get(), std::vector<metric_sdk::MetricData>{supported_histogram}}}};

auto translated = PrometheusExporterUtils::TranslateToPrometheus(
data, /*populate_target_info=*/false, /*without_otel_scope=*/false,
/*without_units=*/false, /*without_type_suffix=*/false);

ASSERT_EQ(translated.size(), 1U);
EXPECT_EQ(translated[0].name, "http_server_duration_seconds");
EXPECT_EQ(translated[0].help, "histogram description");
EXPECT_EQ(translated[0].type, prometheus_client::MetricType::Histogram);
ASSERT_EQ(translated[0].metric.size(), 1U);
EXPECT_EQ(translated[0].metric[0].histogram.sample_count, 4U);
EXPECT_DOUBLE_EQ(translated[0].metric[0].histogram.sample_sum, 45.0);
}

OPENTELEMETRY_END_NAMESPACE
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