[connector/spanmetrics] Fix memory leak

# Why

The `spanmetrics` connector has a memory leak that occurs when the
cumulative temporality is used. The `connectorImp#resourceMetrics` map
is only ever cleaned up in delta temporality.

# What

Turn `connectorImp#resourceMetrics` into a LRU cache with a maximum
size. To correctly handle metric resets we also introduce a start
timestamp per `resourceMetric` instance.

# References

Fixes open-telemetry#27654

Co-authored-by: Jared Tan <[email protected]>

.chloggen/bripkens-spanmetrics-memory-leak.yaml

@@ -0,0 +1,11 @@
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: connector/spanmetrics
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Fix memory leak when the cumulative temporality is used.
+
+# One or more tracking issues related to the change
+issues: [27654]

connector/spanmetricsconnector/README.md

@@ -109,6 +109,8 @@ The following settings can be optionally configured:
   If no `default` is provided, this dimension will be **omitted** from the metric.
 - `exclude_dimensions`: the list of dimensions to be excluded from the default set of dimensions. Use to exclude unneeded data from metrics. 
 - `dimensions_cache_size` (default: `1000`): the size of cache for storing Dimensions to improve collectors memory usage. Must be a positive number. 
+- `resource_metrics_cache_size` (default: `1000`): the size of the cache holding metrics for a service. This is mostly relevant for
+   cumulative temporality to avoid memory leaks and correct metric timestamp resets.
 - `aggregation_temporality` (default: `AGGREGATION_TEMPORALITY_CUMULATIVE`): Defines the aggregation temporality of the generated metrics. 
   One of either `AGGREGATION_TEMPORALITY_CUMULATIVE` or `AGGREGATION_TEMPORALITY_DELTA`.
 - `namespace`: Defines the namespace of the generated metrics. If `namespace` provided, generated metric name will be added `namespace.` prefix.

connector/spanmetricsconnector/config.go

@@ -46,6 +46,11 @@ type Config struct {
 	// Optional. See defaultDimensionsCacheSize in connector.go for the default value.
 	DimensionsCacheSize int `mapstructure:"dimensions_cache_size"`
 
+	// ResourceMetricsCacheSize defines the size of the cache holding metrics for a service. This is mostly relevant for
+	// cumulative temporality to avoid memory leaks and correct metric timestamp resets.
+	// Optional. See defaultResourceMetricsCacheSize in connector.go for the default value.
+	ResourceMetricsCacheSize int `mapstructure:"resource_metrics_cache_size"`
+
 	AggregationTemporality string `mapstructure:"aggregation_temporality"`
 
 	Histogram HistogramConfig `mapstructure:"histogram"`

connector/spanmetricsconnector/config_test.go

@@ -47,8 +47,9 @@ func TestLoadConfig(t *testing.T) {
 					{Name: "http.method", Default: &defaultMethod},
 					{Name: "http.status_code", Default: (*string)(nil)},
 				},
-				DimensionsCacheSize:  1500,
-				MetricsFlushInterval: 30 * time.Second,
+				DimensionsCacheSize:      1500,
+				ResourceMetricsCacheSize: 1600,
+				MetricsFlushInterval:     30 * time.Second,
 				Exemplars: ExemplarsConfig{
 					Enabled: true,
 				},
@@ -66,9 +67,10 @@ func TestLoadConfig(t *testing.T) {
 		{
 			id: component.NewIDWithName(metadata.Type, "exponential_histogram"),
 			expected: &Config{
-				AggregationTemporality: cumulative,
-				DimensionsCacheSize:    1000,
-				MetricsFlushInterval:   15 * time.Second,
+				AggregationTemporality:   cumulative,
+				DimensionsCacheSize:      defaultDimensionsCacheSize,
+				ResourceMetricsCacheSize: defaultResourceMetricsCacheSize,
+				MetricsFlushInterval:     15 * time.Second,
 				Histogram: HistogramConfig{
 					Unit: metrics.Milliseconds,
 					Exponential: &ExponentialHistogramConfig{
@@ -88,11 +90,12 @@ func TestLoadConfig(t *testing.T) {
 		{
 			id: component.NewIDWithName(metadata.Type, "exemplars_enabled"),
 			expected: &Config{
-				AggregationTemporality: "AGGREGATION_TEMPORALITY_CUMULATIVE",
-				DimensionsCacheSize:    defaultDimensionsCacheSize,
-				MetricsFlushInterval:   15 * time.Second,
-				Histogram:              HistogramConfig{Disable: false, Unit: defaultUnit},
-				Exemplars:              ExemplarsConfig{Enabled: true},
+				AggregationTemporality:   "AGGREGATION_TEMPORALITY_CUMULATIVE",
+				DimensionsCacheSize:      defaultDimensionsCacheSize,
+				ResourceMetricsCacheSize: defaultResourceMetricsCacheSize,
+				MetricsFlushInterval:     15 * time.Second,
+				Histogram:                HistogramConfig{Disable: false, Unit: defaultUnit},
+				Exemplars:                ExemplarsConfig{Enabled: true},
 			},
 		},
 	}

connector/spanmetricsconnector/connector.go

@@ -32,7 +32,8 @@ const (
 	statusCodeKey      = "status.code" // OpenTelemetry non-standard constant.
 	metricKeySeparator = string(byte(0))
 
-	defaultDimensionsCacheSize = 1000
+	defaultDimensionsCacheSize      = 1000
+	defaultResourceMetricsCacheSize = 1000
 
 	metricNameDuration = "duration"
 	metricNameCalls    = "calls"
@@ -51,10 +52,7 @@ type connectorImp struct {
 	// Additional dimensions to add to metrics.
 	dimensions []dimension
 
-	// The starting time of the data points.
-	startTimestamp pcommon.Timestamp
-
-	resourceMetrics map[resourceKey]*resourceMetrics
+	resourceMetrics *cache.Cache[resourceKey, *resourceMetrics]
 
 	keyBuf *bytes.Buffer
 
@@ -79,6 +77,8 @@ type resourceMetrics struct {
 	sums       metrics.SumMetrics
 	events     metrics.SumMetrics
 	attributes pcommon.Map
+	// startTimestamp captures when the first data points for this resource are recorded.
+	startTimestamp pcommon.Timestamp
 }
 
 type dimension struct {
@@ -110,11 +110,15 @@ func newConnector(logger *zap.Logger, config component.Config, ticker *clock.Tic
 		return nil, err
 	}
 
+	resourceMetricsCache, err := cache.NewCache[resourceKey, *resourceMetrics](cfg.ResourceMetricsCacheSize)
+	if err != nil {
+		return nil, err
+	}
+
 	return &connectorImp{
 		logger:                logger,
 		config:                *cfg,
-		startTimestamp:        pcommon.NewTimestampFromTime(time.Now()),
-		resourceMetrics:       make(map[resourceKey]*resourceMetrics),
+		resourceMetrics:       resourceMetricsCache,
 		dimensions:            newDimensions(cfg.Dimensions),
 		keyBuf:                bytes.NewBuffer(make([]byte, 0, 1024)),
 		metricKeyToDimensions: metricKeyToDimensionsCache,
@@ -236,7 +240,8 @@ func (p *connectorImp) exportMetrics(ctx context.Context) {
 // buildMetrics collects the computed raw metrics data and builds OTLP metrics.
 func (p *connectorImp) buildMetrics() pmetric.Metrics {
 	m := pmetric.NewMetrics()
-	for _, rawMetrics := range p.resourceMetrics {
+
+	p.resourceMetrics.ForEach(func(_ resourceKey, rawMetrics *resourceMetrics) {
 		rm := m.ResourceMetrics().AppendEmpty()
 		rawMetrics.attributes.CopyTo(rm.Resource().Attributes())
 
@@ -246,42 +251,42 @@ func (p *connectorImp) buildMetrics() pmetric.Metrics {
 		sums := rawMetrics.sums
 		metric := sm.Metrics().AppendEmpty()
 		metric.SetName(buildMetricName(p.config.Namespace, metricNameCalls))
-		sums.BuildMetrics(metric, p.startTimestamp, p.config.GetAggregationTemporality())
+		sums.BuildMetrics(metric, rawMetrics.startTimestamp, p.config.GetAggregationTemporality())
 		if !p.config.Histogram.Disable {
 			histograms := rawMetrics.histograms
 			metric = sm.Metrics().AppendEmpty()
 			metric.SetName(buildMetricName(p.config.Namespace, metricNameDuration))
 			metric.SetUnit(p.config.Histogram.Unit.String())
-			histograms.BuildMetrics(metric, p.startTimestamp, p.config.GetAggregationTemporality())
+			histograms.BuildMetrics(metric, rawMetrics.startTimestamp, p.config.GetAggregationTemporality())
 		}
 
 		events := rawMetrics.events
 		if p.events.Enabled {
 			metric = sm.Metrics().AppendEmpty()
 			metric.SetName(buildMetricName(p.config.Namespace, metricNameEvents))
-			events.BuildMetrics(metric, p.startTimestamp, p.config.GetAggregationTemporality())
+			events.BuildMetrics(metric, rawMetrics.startTimestamp, p.config.GetAggregationTemporality())
 		}
-	}
+	})
 
 	return m
 }
 
 func (p *connectorImp) resetState() {
 	// If delta metrics, reset accumulated data
 	if p.config.GetAggregationTemporality() == pmetric.AggregationTemporalityDelta {
-		p.resourceMetrics = make(map[resourceKey]*resourceMetrics)
+		p.resourceMetrics.Purge()
 		p.metricKeyToDimensions.Purge()
-		p.startTimestamp = pcommon.NewTimestampFromTime(time.Now())
 	} else {
+		p.resourceMetrics.RemoveEvictedItems()
 		p.metricKeyToDimensions.RemoveEvictedItems()
 
 		// Exemplars are only relevant to this batch of traces, so must be cleared within the lock
 		if p.config.Histogram.Disable {
 			return
 		}
-		for _, m := range p.resourceMetrics {
+		p.resourceMetrics.ForEach(func(_ resourceKey, m *resourceMetrics) {
 			m.histograms.Reset(true)
-		}
+		})
 
 	}
 }
@@ -387,15 +392,16 @@ type resourceKey [16]byte
 
 func (p *connectorImp) getOrCreateResourceMetrics(attr pcommon.Map) *resourceMetrics {
 	key := resourceKey(pdatautil.MapHash(attr))
-	v, ok := p.resourceMetrics[key]
+	v, ok := p.resourceMetrics.Get(key)
 	if !ok {
 		v = &resourceMetrics{
-			histograms: initHistogramMetrics(p.config),
-			sums:       metrics.NewSumMetrics(),
-			events:     metrics.NewSumMetrics(),
-			attributes: attr,
+			histograms:     initHistogramMetrics(p.config),
+			sums:           metrics.NewSumMetrics(),
+			events:         metrics.NewSumMetrics(),
+			attributes:     attr,
+			startTimestamp: pcommon.NewTimestampFromTime(time.Now()),
 		}
-		p.resourceMetrics[key] = v
+		p.resourceMetrics.Add(key, v)
 	}
 	return v
 }

connector/spanmetricsconnector/connector_test.go

@@ -32,18 +32,19 @@ import (
 )
 
 const (
-	stringAttrName         = "stringAttrName"
-	intAttrName            = "intAttrName"
-	doubleAttrName         = "doubleAttrName"
-	boolAttrName           = "boolAttrName"
-	nullAttrName           = "nullAttrName"
-	mapAttrName            = "mapAttrName"
-	arrayAttrName          = "arrayAttrName"
-	notInSpanAttrName0     = "shouldBeInMetric"
-	notInSpanAttrName1     = "shouldNotBeInMetric"
-	regionResourceAttrName = "region"
-	exceptionTypeAttrName  = "exception.type"
-	DimensionsCacheSize    = 2
+	stringAttrName           = "stringAttrName"
+	intAttrName              = "intAttrName"
+	doubleAttrName           = "doubleAttrName"
+	boolAttrName             = "boolAttrName"
+	nullAttrName             = "nullAttrName"
+	mapAttrName              = "mapAttrName"
+	arrayAttrName            = "arrayAttrName"
+	notInSpanAttrName0       = "shouldBeInMetric"
+	notInSpanAttrName1       = "shouldNotBeInMetric"
+	regionResourceAttrName   = "region"
+	exceptionTypeAttrName    = "exception.type"
+	dimensionsCacheSize      = 2
+	resourceMetricsCacheSize = 5
 
 	sampleRegion   = "us-east-1"
 	sampleDuration = float64(11)
@@ -881,7 +882,7 @@ func TestMetricKeyCache(t *testing.T) {
 	require.NoError(t, err)
 	// 2 key was cached, 1 key was evicted and cleaned after the processing
 	assert.Eventually(t, func() bool {
-		return p.metricKeyToDimensions.Len() == DimensionsCacheSize
+		return p.metricKeyToDimensions.Len() == dimensionsCacheSize
 	}, 10*time.Second, time.Millisecond*100)
 
 	// consume another batch of traces
@@ -890,10 +891,48 @@ func TestMetricKeyCache(t *testing.T) {
 
 	// 2 key was cached, other keys were evicted and cleaned after the processing
 	assert.Eventually(t, func() bool {
-		return p.metricKeyToDimensions.Len() == DimensionsCacheSize
+		return p.metricKeyToDimensions.Len() == dimensionsCacheSize
 	}, 10*time.Second, time.Millisecond*100)
 }
 
+func TestResourceMetricsCache(t *testing.T) {
+	mcon := consumertest.NewNop()
+
+	p := newConnectorImp(t, mcon, stringp("defaultNullValue"), explicitHistogramsConfig, disabledExemplarsConfig, disabledEventsConfig, cumulative, zaptest.NewLogger(t), nil)
+
+	// Test
+	ctx := metadata.NewIncomingContext(context.Background(), nil)
+
+	// 0 resources in the beginning
+	assert.Zero(t, p.resourceMetrics.Len())
+
+	err := p.ConsumeTraces(ctx, buildSampleTrace())
+	// Validate
+	require.NoError(t, err)
+	assert.Equal(t, 2, p.resourceMetrics.Len())
+
+	// consume another batch of traces for the same resources
+	err = p.ConsumeTraces(ctx, buildSampleTrace())
+	require.NoError(t, err)
+	assert.Equal(t, 2, p.resourceMetrics.Len())
+
+	// consume more batches for new resources. Max size is exceeded causing old resource entries to be discarded
+	for i := 0; i < resourceMetricsCacheSize; i++ {
+		traces := buildSampleTrace()
+
+		// add resource attributes to simulate additional resources providing data
+		for j := 0; j < traces.ResourceSpans().Len(); j++ {
+			traces.ResourceSpans().At(j).Resource().Attributes().PutStr("dummy", fmt.Sprintf("%d", i))
+		}
+
+		err = p.ConsumeTraces(ctx, traces)
+		require.NoError(t, err)
+	}
+
+	// validate that the cache doesn't grow past its limit
+	assert.Equal(t, resourceMetricsCacheSize, p.resourceMetrics.Len())
+}
+
 func BenchmarkConnectorConsumeTraces(b *testing.B) {
 	// Prepare
 	mcon := consumertest.NewNop()
@@ -964,11 +1003,12 @@ func TestExcludeDimensionsConsumeTraces(t *testing.T) {
 func newConnectorImp(t *testing.T, mcon consumer.Metrics, defaultNullValue *string, histogramConfig func() HistogramConfig, exemplarsConfig func() ExemplarsConfig, eventsConfig func() EventsConfig, temporality string, logger *zap.Logger, ticker *clock.Ticker, excludedDimensions ...string) *connectorImp {
 
 	cfg := &Config{
-		AggregationTemporality: temporality,
-		Histogram:              histogramConfig(),
-		Exemplars:              exemplarsConfig(),
-		ExcludeDimensions:      excludedDimensions,
-		DimensionsCacheSize:    DimensionsCacheSize,
+		AggregationTemporality:   temporality,
+		Histogram:                histogramConfig(),
+		Exemplars:                exemplarsConfig(),
+		ExcludeDimensions:        excludedDimensions,
+		DimensionsCacheSize:      dimensionsCacheSize,
+		ResourceMetricsCacheSize: resourceMetricsCacheSize,
 		Dimensions: []Dimension{
 			// Set nil defaults to force a lookup for the attribute in the span.
 			{stringAttrName, nil},

connector/spanmetricsconnector/factory.go

@@ -28,10 +28,11 @@ func NewFactory() connector.Factory {
 
 func createDefaultConfig() component.Config {
 	return &Config{
-		AggregationTemporality: "AGGREGATION_TEMPORALITY_CUMULATIVE",
-		DimensionsCacheSize:    defaultDimensionsCacheSize,
-		MetricsFlushInterval:   15 * time.Second,
-		Histogram:              HistogramConfig{Disable: false, Unit: defaultUnit},
+		AggregationTemporality:   "AGGREGATION_TEMPORALITY_CUMULATIVE",
+		DimensionsCacheSize:      defaultDimensionsCacheSize,
+		ResourceMetricsCacheSize: defaultResourceMetricsCacheSize,
+		MetricsFlushInterval:     15 * time.Second,
+		Histogram:                HistogramConfig{Disable: false, Unit: defaultUnit},
 	}
 }
 

connector/spanmetricsconnector/internal/cache/cache.go

@@ -74,3 +74,17 @@ func (c *Cache[K, V]) Purge() {
 	c.lru.Purge()
 	c.RemoveEvictedItems()
 }
+
+// ForEach iterates over all the items within the cache, as well as the evicted items (if any).
+func (c *Cache[K, V]) ForEach(fn func(k K, v V)) {
+	for _, k := range c.lru.Keys() {
+		v, ok := c.lru.Get(k)
+		if ok {
+			fn(k.(K), v.(V))
+		}
+	}
+
+	for k, v := range c.evictedItems {
+		fn(k, v)
+	}
+}

connector/spanmetricsconnector/testdata/config.yaml

@@ -15,6 +15,7 @@ spanmetrics/full:
   exemplars:
     enabled: true
   dimensions_cache_size: 1500
+  resource_metrics_cache_size: 1600
 
   # Additional list of dimensions on top of:
   # - service.name