[SDK] Cardinality limits for metrics streams (Sync Instruments + Delta Temporality)

sdk/include/opentelemetry/sdk/metrics/state/attributes_hashmap.h

@@ -23,6 +23,15 @@ namespace metrics
 
 using opentelemetry::sdk::common::OrderedAttributeMap;
 
+constexpr size_t kAggregationCardinalityLimit = 2000;
+const std::string kAggregationCardinalityLimitOverflowError =
+    "Maximum data points for metric stream exceeded. Entry added to overflow";
+const std::string kAttributesLimitOverflowKey = "otel.metrics.overflow";
+const bool kAttributesLimitOverflowValue      = true;
+const size_t kOverflowAttributesHash          = common::GetHashForAttributeMap(
+    {{kAttributesLimitOverflowKey,
+      kAttributesLimitOverflowValue}});  // precalculated for optimization
+
 class AttributeHashGenerator
 {
 public:
@@ -35,6 +44,9 @@ class AttributeHashGenerator
 class AttributesHashMap
 {
 public:
+  AttributesHashMap(size_t attributes_limit = kAggregationCardinalityLimit)
+      : attributes_limit_(attributes_limit)
+  {}
   Aggregation *Get(size_t hash) const
   {
     auto it = hash_map_.find(hash);
@@ -66,6 +78,11 @@ class AttributesHashMap
       return it->second.second.get();
     }
 
+    if (IsOverflowAttributes())
+    {
+      return GetOrSetOveflowAttributes(aggregation_callback);
+    }
+
     MetricAttributes attr{attributes};
 
     hash_map_[hash] = {attr, aggregation_callback()};
@@ -80,6 +97,12 @@ class AttributesHashMap
     {
       return it->second.second.get();
     }
+
+    if (IsOverflowAttributes())
+    {
+      return GetOrSetOveflowAttributes(aggregation_callback);
+    }
+
     MetricAttributes attr{};
     hash_map_[hash] = {attr, aggregation_callback()};
     return hash_map_[hash].second.get();
@@ -95,6 +118,11 @@ class AttributesHashMap
       return it->second.second.get();
     }
 
+    if (IsOverflowAttributes())
+    {
+      return GetOrSetOveflowAttributes(aggregation_callback);
+    }
+
     MetricAttributes attr{attributes};
 
     hash_map_[hash] = {attr, aggregation_callback()};
@@ -113,6 +141,12 @@ class AttributesHashMap
     {
       it->second.second = std::move(aggr);
     }
+    else if (IsOverflowAttributes())
+    {
+      hash_map_[kOverflowAttributesHash] = {
+          MetricAttributes{{kAttributesLimitOverflowKey, kAttributesLimitOverflowValue}},
+          std::move(aggr)};
+    }
     else
     {
       MetricAttributes attr{attributes};
@@ -127,6 +161,12 @@ class AttributesHashMap
     {
       it->second.second = std::move(aggr);
     }
+    else if (IsOverflowAttributes())
+    {
+      hash_map_[kOverflowAttributesHash] = {
+          MetricAttributes{{kAttributesLimitOverflowKey, kAttributesLimitOverflowValue}},
+          std::move(aggr)};
+    }
     else
     {
       MetricAttributes attr{attributes};
@@ -157,6 +197,29 @@ class AttributesHashMap
 
 private:
   std::unordered_map<size_t, std::pair<MetricAttributes, std::unique_ptr<Aggregation>>> hash_map_;
+  size_t attributes_limit_;
+
+  Aggregation *GetOrSetOveflowAttributes(
+      std::function<std::unique_ptr<Aggregation>()> aggregation_callback)
+  {
+    auto agg = aggregation_callback();
+    return GetOrSetOveflowAttributes(std::move(agg));
+  }
+
+  Aggregation *GetOrSetOveflowAttributes(std::unique_ptr<Aggregation> agg)
+  {
+    auto it = hash_map_.find(kOverflowAttributesHash);
+    if (it != hash_map_.end())
+    {
+      return it->second.second.get();
+    }
+
+    MetricAttributes attr{{kAttributesLimitOverflowKey, kAttributesLimitOverflowValue}};
+    hash_map_[kOverflowAttributesHash] = {attr, std::move(agg)};
+    return hash_map_[kOverflowAttributesHash].second.get();
+  }
+
+  bool IsOverflowAttributes() const { return (hash_map_.size() + 1 >= attributes_limit_); }
 };
 }  // namespace metrics
 

sdk/include/opentelemetry/sdk/metrics/state/sync_metric_storage.h

@@ -40,9 +40,10 @@ class SyncMetricStorage : public MetricStorage, public SyncWritableMetricStorage
                     const AttributesProcessor *attributes_processor,
                     nostd::shared_ptr<ExemplarReservoir> &&exemplar_reservoir
                         OPENTELEMETRY_MAYBE_UNUSED,
-                    const AggregationConfig *aggregation_config)
+                    const AggregationConfig *aggregation_config,
+                    size_t attributes_limit = kAggregationCardinalityLimit)
       : instrument_descriptor_(instrument_descriptor),
-        attributes_hashmap_(new AttributesHashMap()),
+        attributes_hashmap_(new AttributesHashMap(attributes_limit)),
         attributes_processor_(attributes_processor),
 #ifdef ENABLE_METRICS_EXEMPLAR_PREVIEW
         exemplar_reservoir_(exemplar_reservoir),

sdk/test/metrics/CMakeLists.txt

@@ -16,6 +16,7 @@ foreach(
   attributes_hashmap_test
   base2_exponential_histogram_indexer_test
   circular_buffer_counter_test
+  cardinality_limit_test
   histogram_test
   sync_metric_storage_counter_test
   sync_metric_storage_histogram_test

sdk/test/metrics/cardinality_limit_test.cc

@@ -0,0 +1,108 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+#include "common.h"
+#include "opentelemetry/common/key_value_iterable_view.h"
+#include "opentelemetry/sdk/metrics/aggregation/sum_aggregation.h"
+#include "opentelemetry/sdk/metrics/instruments.h"
+#include "opentelemetry/sdk/metrics/state/attributes_hashmap.h"
+#include "opentelemetry/sdk/metrics/state/sync_metric_storage.h"
+
+#include <gtest/gtest.h>
+#include <functional>
+
+using namespace opentelemetry::sdk::metrics;
+using namespace opentelemetry::common;
+namespace nostd = opentelemetry::nostd;
+
+TEST(CardinalityLimit, AttributesHashMapBasicTests)
+{
+  AttributesHashMap hash_map(10);
+  std::function<std::unique_ptr<Aggregation>()> aggregation_callback =
+      []() -> std::unique_ptr<Aggregation> {
+    return std::unique_ptr<Aggregation>(new LongSumAggregation(true));
+  };
+  // add 10 unique metric points. 9 should be added to hashmap, 10th should be overflow.
+  long record_value = 100;
+  for (auto i = 0; i < 10; i++)
+  {
+    OrderedAttributeMap attributes = {{"key", std::to_string(i)}};
+    auto hash                      = opentelemetry::sdk::common::GetHashForAttributeMap(attributes);
+    static_cast<LongSumAggregation *>(
+        hash_map.GetOrSetDefault(attributes, aggregation_callback, hash))
+        ->Aggregate(record_value);
+  }
+  EXPECT_EQ(hash_map.Size(), 10);
+  // add 5 unique metric points above limit, they all should get consolidated as single
+  // overflowmetric point.
+  for (auto i = 10; i < 15; i++)
+  {
+    OrderedAttributeMap attributes = {{"key", std::to_string(i)}};
+    auto hash                      = opentelemetry::sdk::common::GetHashForAttributeMap(attributes);
+    static_cast<LongSumAggregation *>(
+        hash_map.GetOrSetDefault(attributes, aggregation_callback, hash))
+        ->Aggregate(record_value);
+  }
+  EXPECT_EQ(hash_map.Size(), 10);  // only one more metric point should be added as overflow.
+  // get the overflow metric point
+  auto agg = hash_map.GetOrSetDefault(
+      OrderedAttributeMap({{kAttributesLimitOverflowKey, kAttributesLimitOverflowValue}}),
+      aggregation_callback, kOverflowAttributesHash);
+  EXPECT_NE(agg, nullptr);
+  auto sum_agg = static_cast<LongSumAggregation *>(agg);
+  EXPECT_EQ(nostd::get<int64_t>(nostd::get<SumPointData>(sum_agg->ToPoint()).value_),
+            record_value * 6);  // 1 from previous 10, 5 from current 5.
+}
+
+class WritableMetricStorageCardinalityLimitTestFixture
+    : public ::testing::TestWithParam<AggregationTemporality>
+{};
+
+TEST_P(WritableMetricStorageCardinalityLimitTestFixture, LongCounterSumAggregation)
+{
+  auto sdk_start_ts               = std::chrono::system_clock::now();
+  const size_t attributes_limit   = 10;
+  InstrumentDescriptor instr_desc = {"name", "desc", "1unit", InstrumentType::kCounter,
+                                     InstrumentValueType::kLong};
+  std::unique_ptr<DefaultAttributesProcessor> default_attributes_processor{
+      new DefaultAttributesProcessor{}};
+  SyncMetricStorage storage(instr_desc, AggregationType::kSum, default_attributes_processor.get(),
+                            ExemplarReservoir::GetNoExemplarReservoir(), nullptr, attributes_limit);
+
+  long record_value = 100;
+  // add 9 unique metric points, and 6 more above limit.
+  for (auto i = 0; i < 15; i++)
+  {
+    std::map<std::string, std::string> attributes = {{"key", std::to_string(i)}};
+    storage.RecordLong(record_value,
+                       KeyValueIterableView<std::map<std::string, std::string>>(attributes),
+                       opentelemetry::context::Context{});
+  }
+  AggregationTemporality temporality = GetParam();
+  std::shared_ptr<CollectorHandle> collector(new MockCollectorHandle(temporality));
+  std::vector<std::shared_ptr<CollectorHandle>> collectors;
+  collectors.push_back(collector);
+  //... Some computation here
+  auto collection_ts      = std::chrono::system_clock::now();
+  size_t count_attributes = 0;
+  bool overflow_present   = false;
+  storage.Collect(
+      collector.get(), collectors, sdk_start_ts, collection_ts, [&](const MetricData &metric_data) {
+        for (const auto &data_attr : metric_data.point_data_attr_)
+        {
+          const auto &data = opentelemetry::nostd::get<SumPointData>(data_attr.point_data);
+          count_attributes++;
+          if (data_attr.attributes.begin()->first == kAttributesLimitOverflowKey)
+          {
+            EXPECT_EQ(nostd::get<int64_t>(data.value_), record_value * 6);
+            overflow_present = true;
+          }
+        }
+        return true;
+      });
+  EXPECT_EQ(count_attributes, attributes_limit);
+  EXPECT_EQ(overflow_present, true);
+}
+INSTANTIATE_TEST_SUITE_P(All,
+                         WritableMetricStorageCardinalityLimitTestFixture,
+                         ::testing::Values(AggregationTemporality::kDelta));